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Check-in Number: 2562
Date: 2002-Oct-07 16:00:38 (local)
2002-Oct-07 14:00:38 (UTC)
User:rse
Branch:
Comment: add more brainstorming stuff from RSE
Tickets:
Inspections:
Files:
ossp-pkg/sio/BRAINSTORM/Apache-Dean-Thoughts.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/CS95-441.ps.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/CS95-441.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/IO-Lite-TR97-269.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/IO-Lite-iol98.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/IO-Lite-presentation.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/IO-Lite.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/IO.MAIL      added-> 1.1
ossp-pkg/sio/BRAINSTORM/apache-stackedio      added-> 1.1
ossp-pkg/sio/BRAINSTORM/asf-ideas.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/brustoloni-abs.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/brustoloni-abs.txt.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/c10k.html      added-> 1.1
ossp-pkg/sio/BRAINSTORM/c10k.html.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/c10k.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/copyavoid.pdf      added-> 1.1
ossp-pkg/sio/BRAINSTORM/copyavoid.pdf.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/copyavoid.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/dean.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_SFmtg.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_bucket_brigades.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_dean_iol.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_greg_filters.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_page_io.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_stacked_io.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/doc_wishes.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/ewa.thesis.ps.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/ewa.thesis.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/infocom98.ps.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/infocom98.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/io-events.html      added-> 1.1
ossp-pkg/sio/BRAINSTORM/io-events.html.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/io-events.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/iolib-eval-rse.txt      added-> 1.1
ossp-pkg/sio/BRAINSTORM/osdi96.ps.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/osdi96.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/smli_tr-95-39.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/smli_tr-95-39.pdf      added-> 1.1
ossp-pkg/sio/BRAINSTORM/smli_tr-95-39.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/smli_tr-99-76.ps      added-> 1.1
ossp-pkg/sio/BRAINSTORM/splice.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/splice.ps.gz.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/thesis.ps.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/thesis.ps.gz      added-> 1.1
ossp-pkg/sio/BRAINSTORM/tr96-169.ps.L      added-> 1.1
ossp-pkg/sio/BRAINSTORM/tr96-169.ps.gz      added-> 1.1

ossp-pkg/sio/BRAINSTORM/Apache-Dean-Thoughts.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
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--- 1,114 ----
+ From dgaudet@arctic.org Mon Jun 28 19:06:50 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: dgaudet@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: async routines
+ Date: 28 Jun 1999 17:33:24 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 96
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.3.96dg4.990628081527.31647G-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 930584004 99816 141.1.129.1 (28 Jun 1999 15:33:24 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Jun 1999 15:33:24 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:31280
+ 
+ [hope you don't mind me cc'ing new-httpd zach, I think others will be
+ interested.]
+ 
+ On Mon, 28 Jun 1999, Zach Brown wrote:
+ 
+ > so dean, I was wading through the mpm code to see if I could munge the
+ > sigwait stuff into it.
+ > 
+ > as far as I could tell, the http protocol routines are still blocking.
+ > what does the future hold in the way for async routines? :)  I basically
+ > need a way to do something like..
+ 
+ You're still waiting for me to get the async stuff in there... I've done
+ part of the work -- the BUFF layer now supports non-blocking sockets. 
+ 
+ However, the HTTP code will always remain blocking.  There's no way I'm
+ going to try to educate the world in how to write async code... and since
+ our HTTP code has arbitrary call outs to third party modules... It'd
+ have a drastic effect on everyone to make this change.
+ 
+ But I honestly don't think this is a problem.  Here's my observations:
+ 
+ All the popular HTTP clients send their requests in one packet (or two
+ in the case of a POST and netscape).  So the HTTP code would almost
+ never have to block while processing the request.  It may block while
+ processing a POST -- something which someone else can worry about later,
+ my code won't be any worse than what we already have in apache.  So
+ any effort we put into making the HTTP parsing code async-safe would
+ be wasted on the 99.9% case.
+ 
+ Most responses fit in the socket's send buffer, and again don't require
+ async support.  But we currently do the lingering_close() routine which
+ could easily use async support.  Large responses also could use async
+ support.
+ 
+ The goal of HTTP parsing is to figure out which response object to
+ send.  In most cases we can reduce that to a bunch of common response
+ types:
+ 
+ - copying a file to the socket
+ - copying a pipe/socket to the socket  (IPC, CGIs)
+ - copying a mem region to the socket (mmap, some dynamic responses)
+ 
+ So what we do is we modify the response handlers only.  We teach them
+ about how to send async responses.
+ 
+ There will be a few new primitives which will tell the core "the response
+ fits one of these categories, please handle it".  The core will do the
+ rest -- and for MPMs which support async handling, the core will return
+ to the MPM and let the MPM do the work async...  the MPM will call a
+ completion function supplied by the core.  (Note that this will simplify
+ things for lots of folks... for example, it'll let us move range request
+ handling to a common spot so that more than just default_handler
+ can support it.)
+ 
+ I expect this to be a simple message passing protocol (pass by reference).
+ Well rather, that's how I expect to implement it in ASH -- where I'll
+ have a single thread per-process doing the select/poll stuff; and the
+ other threads are in a pool that handles the protocol stuff.  For your
+ stuff you may want to do it another way -- but we'll be using a common
+ structure that the core knows about... and that structure will look like
+ a message:
+ 
+     struct msg {
+        enum {
+            MSG_SEND_FILE,
+            MSG_SEND_PIPE,
+            MSG_SEND_MEM,
+            MSG_LINGERING_CLOSE,
+            MSG_WAIT_FOR_READ,  /* for handling keep-alives */
+            ...
+        } type;
+        BUFF *client;
+        void (*completion)(struct msg *, int status);
+        union {
+            ... extra data here for whichver types need it ...;
+        } x;
+     };
+ 
+ The nice thing about this is that these operations are protocol
+ independant... at this level there's no knowledge of HTTP, so the same
+ MPM core could be used to implement other protocols.
+ 
+ > so as I was thinking about this stuff, I realized it might be neat to have
+ > 'classes' of non blocking pending work and have different threads with
+ > differnt priorities hacking on it.  Say we have a very high priority
+ > thread that accepts connectoins, does initial header parsing, and
+ > sendfile()ing data out.  We could have lower priority threads that are
+ > spinning doing 'harder' BUFF work like an encryption layer or gziping
+ > content, whatever.
+ 
+ You should be able to implement this in your MPM easily I think... because
+ you'll see the different message types and can distribute them as needed.
+ 
+ Dean
+ 


ossp-pkg/sio/BRAINSTORM/CS95-441.ps.L -> 1.1

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+ http://www.cs.ucsd.edu/groups/csl/pubs/conf/sosp95.html


ossp-pkg/sio/BRAINSTORM/CS95-441.ps.gz -> 1.1

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ossp-pkg/sio/BRAINSTORM/IO-Lite-TR97-269.ps.gz -> 1.1

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ossp-pkg/sio/BRAINSTORM/IO-Lite-iol98.ps.gz -> 1.1

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ossp-pkg/sio/BRAINSTORM/IO-Lite.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
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+ From jg@pa.dec.com Wed Mar  3 08:37:08 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: jg@pa.dec.com (Jim Gettys)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: OSDI paper - IO-Lite: A Unified I/O Buffering and Caching System
+ Date: 3 Mar 1999 07:14:53 +0100
+ Organization: Mail2News at engelschall.com
+ Lines: 56
+ Approved: postmaster@m2ndom
+ Message-ID: <9903021931.AA13619@pachyderm.pa.dec.com>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 920441693 44447 141.1.129.1 (3 Mar 1999 06:14:53 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 3 Mar 1999 06:14:53 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:29016
+ 
+ I am doing something that I seldom do: cross posting between two high volume
+ mailing lists. (linux-kernel and the Apache developer's lists). Sometimes
+ it is useful for us folks who build applications to attend base operating
+ system conferences, which I had not for a while.
+ 
+ I encourage everyone to read the paper:
+ 
+ IO-Lite: A Unified I/O Buffering and Caching System, by Vivek Pai, Peter
+ Druschel, and Willy Zwaenepoel, published in the 3rd Symposium on Operating
+ Systems Design and Implementation (OSDI '99) Proceedings, New Orleans,
+ Louisiana, February 22-25, 1999, pp15-28.
+ 
+ http://www.cs.rice.edu/~vivek/iol98/    (OSDI paper)
+ http://www.cs.rice.edu/~vivek/vivekmsee/ (MS thesis)
+ 
+ At the latest (3rd) Symposium on Operating System Design and Implementation,
+ the "best of conference" award went to this paper, which reports on both
+ the design and implementation of a unified IO scheme.  I think the award was
+ well placed.
+ 
+ It shows a new I/O approach that is very general and flexible, and avoids
+ data copies with minimal overhead, even between processes.  The authors
+ use as an example Web service, and show very good performance gains. 
+ 
+ While I believe the paper overstates the benefits for "vanilla" web service, 
+ for CGI it should clearly be a major win.  IO-Lite avoids the redundant 
+ data copies that normally occur in the standard UNIX read/write semantics, 
+ and copies in the network layer. 
+ 
+ My intution tells me that the interfaces proposed here should be very 
+ useful for a very wide range of applications (including a certain window 
+ system I'm a bit fond of, which already took advantage of writev; the 
+ IO-Lite interfaces look better to me).
+ 
+ For full benefits to be reaped, an application can use new system call 
+ interfaces that IO-Lite introduces.  The immediate application that comes 
+ to my mind is Apache (ergo the cross posting), particularly as Apache 
+ thinks through its V2 design.  I hope that we can have a productive 
+ discussion and this thread may be able to provide clarification (I cc'ed 
+ the authors of the paper), and encourage IO-Lite's adoption.
+ 
+ This has been implemented in FreeBSD... And, of course, it would be nice
+ to have it in Linux as well, and for Apache to be able to take full
+ advantage of IO-Lite.
+ 
+                                - Jim Gettys
+ 
+ 
+ --
+ Jim Gettys
+ Industry Standards and Consortia
+ Compaq Computer Corporation
+ Visting Scientist, World Wide Web Consortium, M.I.T.
+ http://www.w3.org/People/Gettys/
+ jg@w3.org, jg@pa.dec.com
+ 


ossp-pkg/sio/BRAINSTORM/IO.MAIL -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
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*** 0 ****
--- 1,39 ----
+ From fielding@kiwi.ics.uci.edu Sat Apr 17 13:19:21 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: fielding@kiwi.ics.uci.edu ("Roy T. Fielding")
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: New idea for apr types.
+ Date: 17 Apr 1999 07:02:19 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 21
+ Approved: postmaster@m2ndom
+ Message-ID: <9904161620.aa25418@paris.ics.uci.edu>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 924325339 88339 141.1.129.1 (17 Apr 1999 05:02:19 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 17 Apr 1999 05:02:19 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:29882
+ 
+ >The basic idea, is to have apr types implemented as objects.  Each type
+ >has a pointer to every function that is allowed by that type.  So,
+ >connection types (apr_socket_t, apr_corba_t, apr_sna_t, apr_netbeui_t,
+ >etc) all implement the same basic functions (read, write, create, close,
+ >shutdown, etc), and each type contains a pointer to those functions.
+ >
+ >Then, all connection types could be referred to as void *, and the type
+ >itself would determine how it should do things under the covers.
+ >
+ >This would allow Apache to run over ANY network type, as long as there was
+ >an apr layer written for it.
+ 
+ Ummm, yeah, it is called stacked disciplines in sfio, stream pipes in
+ Onions (my Ada95 library that nobody uses), buffer slices in IO-Lite,
+ streams in W3C-libwww, or layered I/O in the 2.0 wish list.
+ 
+ I'm all for it, though I'd use my bucket brigade from Onions and the
+ IO-Lite memory stuff (assuming sfio wasn't good enough).
+ 
+ ....Roy
+ 


ossp-pkg/sio/BRAINSTORM/apache-stackedio -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
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--- 1,883 ----
+ [djg: comments like this are from dean]
+ 
+ This past summer, Alexei and I wrote a spec for an I/O Filters API... 
+ this proposal addresses one part of that -- 'stacked' I/O with buff.c. 
+ 
+ We have a couple of options for stacked I/O: we can either use existing
+ code, such as sfio, or we can rewrite buff.c to do it.  We've gone over
+ the first possibility at length, though, and there were problems with each
+ implemenation which was mentioned (licensing and compatibility,
+ specifically); so far as I know, those remain issues. 
+ 
+ Btw -- sfio will be supported w/in this model... it just wouldn't be the
+ basis for the model's implementation. 
+ 
+      -- Ed Korthof        |  Web Server Engineer --
+      -- ed@organic.com    |  Organic Online, Inc --
+      -- (415) 278-5676    |  Fax: (415) 284-6891 --
+ 
+ ---------------------------------------------------------------------------
+ Stacked I/O With BUFFs
+        Sections:
+ 
+        1.) Overview
+        2.) The API
+                User-supplied structures
+                API functions
+        3.) Detailed Description
+                The bfilter structure
+                The bbottomfilter structure
+                The BUFF structure
+                Public functions in buff.c
+        4.) Efficiency Considerations
+                Buffering
+                Memory copies
+                Function chaining
+                writev
+        5.) Code in buff.c
+                Default Functions
+                Heuristics for writev
+                Writing
+                Reading
+                Flushing data
+                Closing stacks and filters
+                Flags and Options
+ 
+ *************************************************************************
+                Overview
+ 
+ The intention of this API is to make Apache's BUFF structure modular
+ while retaining high efficiency.  Basically, it involves rewriting
+ buff.c to provide 'stacked' I/O -- where the data passed through a
+ series of 'filters', which may modify it.
+ 
+ There are two parts to this, the core code for BUFF structures, and the
+ "filters" used to implement new behavior.  "filter" is used to refer to
+ both the sets of 5 functions, as shown in the bfilter structure in the
+ next section, and to BUFFs which are created using a specific bfliter.
+ These will also be occasionally refered to as "user-supplied", though
+ the Apache core will need to use these as well for basic functions.
+ 
+ The user-supplied functions should use only the public BUFF API, rather
+ than any internal details or functions.  One thing which may not be
+ clear is that in the core BUFF functions, the BUFF pointer passed in
+ refers to the BUFF on which the operation will happen.  OTOH, in the
+ user-supplied code, the BUFF passed in is the next buffer down the
+ chain, not the current one.
+ 
+ *************************************************************************
+                The API
+ 
+        User-supplied structures
+ 
+ First, the bfilter structure is used in all filters:
+     typedef struct {
+       int (*writev)(BUFF *, void *, struct iovect *, int);
+       int (*read)(BUFF *, void *, char *, int);
+       int (*write)(BUFF *, void *, const char *, int);
+       int (*flush)(BUFF *, void *, const char *, int, bfilter *);
+       int (*transmitfile)(BUFF *, void *, file_info_ptr *);
+       void (*close)(BUFF *, void *);
+     } bfilter;
+ 
+ bfilters are placed into a BUFF structure along with a
+ user-supplied void * pointer.
+ 
+ Second, the following structure is for use with a filter which can
+ sit at the bottom of the stack:
+ 
+     typedef struct {
+       void *(*bgetfileinfo)(BUFF *, void *);
+       void (*bpushfileinfo)(BUFF *, void *, void *);
+     } bbottomfilter;
+ 
+ 
+        BUFF API functions
+ 
+ The following functions are new BUFF API functions:
+ 
+ For filters:
+ 
+ BUFF * bcreatestack(pool *p, int flags, struct bfilter *,
+                     struct bbottomfilter *, void *);
+ BUFF * bpushfilter (BUFF *, struct bfilter *, void *);
+ BUFF * bpushbuffer (BUFF *, BUFF *);
+ BUFF * bpopfilter(BUFF *);
+ BUFF * bpopbuffer(BUFF *);
+ void bclosestack(BUFF *);
+ 
+ For BUFFs in general:
+ 
+ int btransmitfile(BUFF *, file_info_ptr *);
+ int bsetstackopts(BUFF *, int, const void *);
+ int bsetstackflags(BUFF *, int, int);
+ 
+ Note that a new flag is needed for bsetstackflags:
+ B_MAXBUFFERING
+ 
+ The current bcreate should become
+ 
+ BUFF * bcreatebuffer (pool *p, int flags, struct bfilter *, void *);
+ 
+ *************************************************************************
+                Detailed Explanation
+ 
+        bfilter structure
+ 
+ The void * pointer used in all these functions, as well as those in the
+ bbottomfilter structure and the filter API functions, is always the same
+ pointer w/in an individual BUFF.
+ 
+ The first function in a bfilter structure is 'writev'; this is only
+ needed for high efficiency writing, generally at the level of the system
+ interface.  In it's absence, multiple writes will be done w/ 'write'.
+ Note that defining 'writev' means you must define 'write'.
+ 
+ The second is 'write'; this is the generic writing function, taking a BUFF
+ * to which to write, a block of text, and the length of that block of
+ text.  The expected return is the number of characters (out of that block
+ of text) which were successfully processed (rather than the number of
+ characters actually written). 
+ 
+ The third is 'read'; this is the generic reading function, taking a BUFF *
+ from which to read data, and a void * buffer in which to put text, and the
+ number of characters to put in that buffer.  The expected return is the
+ number of characters placed in the buffer.
+ 
+ The fourth is 'flush'; this is intended to force the buffer to spit out
+ any data it may have been saving, as well as to clear any data the
+ BUFF code was storing.  If the third argument is non-null, then it
+ contains more text to be printed; that text need not be null terminated,
+ but the fourth argument contains the length of text to be processed.  The
+ expected return value should be the number of characters handled out
+ from the third argument (0 if there are none), or -1 on error.  Finally,
+ the fifth argument is a pointer to the bfilter struct containing this
+ function, so that it may use the write or writev functions in it.   Note
+ that general buffering is handled by BUFF's internal code, and module
+ writers should not store data for performance reasons.
+ 
+ The fifth is 'transmitfile', which takes as its arguments a buffer to
+ which to write (if non-null), the void * pointer containing configuration
+ (or other) information for this filter, and a system-dependent pointer
+ (the file_info_ptr structure will be defined on a per-system basis)
+ containing information required to print the 'file' in question.
+ This is intended to allow zero-copy TCP in Win32.
+ 
+ The sixth is 'close'; this is what is called when the connection is being
+ closed.  The 'close' should not be passed on to the next filter in the
+ stack.  Most filters will not need to use this, but if database handles
+ or some other object is created, this is the point at which to remove it.
+ Note that flush is called automatically before this.
+ 
+        bbottomfilter Structure
+ 
+ The first function, bgetfileinfo, is designed to allow Apache to get
+ information from a BUFF struct regarding the input and output sources.
+ This is currently used to get the input file number to select on a
+ socket to see if there's data waiting to be read.  The information
+ returned is platform specific; the void * pointer passed in holds
+ the void * pointer passed to all user-supplied functions.
+ 
+ The second function, bpushfileinfo, is used to push file information
+ onto a buffer, so that the buffer can be fully constructed and ready
+ to handle data as soon as possible after a client has connected.
+ The first void * pointer holds platform specific information (in
+ Unix, it would be a pair of file descriptors); the second holds the
+ void * pointer passed to all user-supplied functions.
+ 
+ [djg: I don't think I really agree with the distinction here between
+ the bottom and the other filters.  Take the select() example, it's
+ valid for any layer to define a fd that can be used for select...
+ in fact it's the topmost layer that should really get to make this
+ definition.  Or maybe I just have your top and bottom flipped.  In
+ any event I think this should be part of the filter structure and
+ not separate.]
+ 
+        The BUFF structure
+ 
+ A couple of changes are needed for this structure: remove fd and
+ fd_in; add a bfilter structure; add a pointer to a bbottomfilter;
+ add three pointers to the next BUFFs: one for the next BUFF in the
+ stack, one for the next BUFF which implements write, and one
+ for the next BUFF which implements read.
+ 
+ 
+        Public functions in buff.c
+ 
+ BUFF * bpushfilter (BUFF *, struct bfilter *, void *);
+ 
+ This function adds the filter functions from bfilter, stacking them on
+ top of the BUFF.  It returns the new top BUFF, or NULL on error.
+ 
+ BUFF * bpushbuffer (BUFF *, BUFF *);
+ 
+ This function places the second buffer on the top of the stack that
+ the first one is on.  It returns the new top BUFF, or NULL on error.
+ 
+ BUFF * bpopfilter(BUFF *);
+ BUFF * bpopbuffer(BUFF *);
+ 
+ Unattaches the top-most filter from the stack, and returns the new
+ top-level BUFF, or NULL on error or when there are no BUFFs
+ remaining.  The two are synonymous.
+ 
+ void bclosestack(BUFF *);
+ 
+ Closes the I/O stack, removing all the filters in it.
+ 
+ BUFF * bcreatestack(pool *p, int flags, struct bfilter *,
+                     struct bbottomfilter *, void *);
+ 
+ This creates an I/O stack.  It returns NULL on error.
+ 
+ BUFF * bcreatebuffer(pool *p, int flags, struct bfilter *, void *);
+ 
+ This creates a BUFF for later use with bpushbuffer.  The BUFF is
+ not set up to be used as an I/O stack, however.  It returns NULL
+ on error.
+ 
+ int bsetstackopts(BUFF *, int, const void *);
+ int bsetstackflags(BUFF *, int, int);
+ 
+ These functions, respectively, set options on all the BUFFs in a
+ stack.  The new flag, B_MAXBUFFERING is used to disable a feature
+ described in the next section, whereby only the first and last
+ BUFFs will buffer data.
+ 
+ *************************************************************************
+                Efficiency Considerations
+ 
+        Buffering
+ 
+ All input and output is buffered by the standard buffering code.
+ People writing code to use buff.c should not concern themselves with
+ buffering for efficiency, and should not buffer except when necessary.
+ 
+ The write function will typically be called with large blocks of text;
+ the read function will attempt to place the specified number of bytes
+ into the buffer.
+ 
+ Dean noted that there are possible problems w/ multiple buffers;
+ further, some applications must not be buffered.  This can be
+ partially dealt with by turning off buffering, or by flushing the
+ data when appropriate.
+ 
+ However, some potential problems arise anyway.  The simplest example
+ involves shrinking transformations; suppose that you have a set
+ of filters, A, B, and C, such that A outputs less text than it
+ recieves, as does B (say A strips comments, and B gzips the result).
+ Then after a write to A which fills the buffer, A writes to B.
+ However, A won't write enough to fill B's buffer, so a memory copy
+ will be needed.  This continues till B's buffer fills up, then
+ B will write to C's buffer -- with the same effect.
+ 
+ [djg: I don't think this is the issue I was really worried about --
+ in the case of shrinking transformations you are already doing 
+ non-trivial amounts of CPU activity with the data, and there's
+ no copying of data that you can eliminate anyway.  I do recognize
+ that there are non-CPU intensive filters -- such as DMA-capable
+ hardware crypto cards.  I don't think they're hard to support in
+ a zero-copy manner though.]
+ 
+ The maximum additional number of bytes which will be copied in this
+ scenario is on the order of nk, where n is the total number of bytes,
+ and k is the number of filters doing shrinking transformations.
+ 
+ There are several possible solutions to this issue.  The first
+ is to turn off buffering in all but the first filter and the
+ last filter.  This reduces the number of unnecessary byte copies
+ to at most one per byte, however it means that the functions in
+ the stack will get called more frequently; but it is the default
+ behavior, overridable by setting the B_MAXBUFFERING with
+ bsetstackflags.  Most filters won't involve a net shrinking
+ transformation, so even this will rarely be an issue; however,
+ if the filters do involve a net shrinking transformation, for
+ the sake of network-efficiency (sending reasonably sized blocks),
+ it may be more efficient anyway.
+ 
+ A second solution is more general use of writev for communication
+ between different buffers.  This complicates the programing work,
+ however.
+ 
+ 
+        Memory copies
+ 
+ Each write function is passed a pointer to constant text; if any changes
+ are being made to the text, it must be copied.  However, if no changes
+ are made to the text (or to some smaller part of it), then it may be
+ sent to the next filter without any additional copying.  This should
+ provide the minimal necessary memory copies.
+ 
+ [djg: Unfortunately this makes it hard to support page-flipping and
+ async i/o because you don't have any reference counts on the data.
+ But I go into a little detail that already in docs/page_io.]
+ 
+        Function chaining
+ 
+ In order to avoid unnecessary function chaining for reads and writes,
+ when a filter is pushed onto the stack, the buff.c code will determine
+ which is the next BUFF which contains a read or write function, and
+ reads and writes, respectively, will go directly to that BUFF.
+ 
+        writev
+ 
+ writev is a function for efficient writing to the system; in terms of
+ this API, however, it also works for dealing with multiple blocks of
+ text without doing unnecessary byte copies.  It is not required.
+ 
+ Currently, the system level writev is used in two contexts: for
+ chunking and when a block of text is writen which, combined with
+ the text already in the buffer, would make the buffer overflow.
+ 
+ writev would be implemented both by the default bottom level filter
+ and by the chunking filter for these operations.  In addition, writev
+ may, be used, as noted above, to pass multiple blocks of text w/o
+ copying them into a single buffer.  Note that if the next filter does
+ not implement writev, however, this will be equivalent to repeated
+ calls to write, which may or may not be more efficient.  Up to
+ IOV_MAX-2 blocks of text may be passed along in this manner.  Unlike
+ the system writev call, the writev in this API should be called only
+ once, with a array with iovec's and a count as to the number of
+ iovecs in it.
+ 
+ If a bfilter defines writev, writev will be called whether or not
+ NO_WRITEV is set; hence, it should deal with that case in a reasonable
+ manner.
+ 
+ [djg: We can't guarantee atomicity of writev() when we emulate it.
+ Probably not a problem, just an observation.]
+ 
+ *************************************************************************
+                Code in buff.c
+ 
+        Default Functions
+ 
+ The default actions are generally those currently performed by Apache,
+ save that they they'll only attempt to write to a buffer, and they'll
+ return an error if there are no more buffers.  That is, you must implement
+ read, write, and flush in the bottom-most filter.
+ 
+ Except for close(), the default code will simply pass the function call
+ on to the next filter in the stack.  Some samples follow.
+ 
+        Heuristics for writev
+ 
+ Currently, we call writev for chunking, and when we get a enough so that
+ the total overflows the buffer.  Since chunking is going to become a
+ filter, the chunking filter will use writev; in addition, bwrite will
+ trigger bwritev as shown (note that system specific information should
+ be kept at the filter level):
+ 
+ in bwrite:
+ 
+     if (fb->outcnt > 0 && nbyte + fb->outcnt >= fb->bufsiz) {
+         /* build iovec structs */
+         struct iovec vec[2];
+         vec[0].iov_base = (void *) fb->outbase;
+         vec[0].iov_len = fb->outcnt;
+         fb->outcnt = 0;
+         vec[1].iov_base = (void *)buff;
+         vec[1].iov_length = nbyte;
+         return bwritev (fb, vec, 2);
+     } else if (nbye >= fb->bufsiz) {
+         return write_with_errors(fb,buff,nbyte);
+     }
+ 
+ Note that the code above takes the place of large_write (as well
+ as taking code from it).
+ 
+ So, bwritev would look something like this (copying and pasting freely
+ from the current source for writev_it_all, which could be replaced):
+ 
+ -----
+ int bwritev (BUFF * fb, struct iovec * vec, int nvecs) {
+     if (!fb)
+         return -1; /* the bottom level filter implemented neither write nor
+                     * writev. */
+     if (fb->bfilter.bwritev) {
+         return bf->bfilter.writev(fb->next, vec, nvecs);
+     } else if (fb->bfilter.write) {
+         /* while it's nice an easy to build the vector and crud, it's painful
+          * to deal with partial writes (esp. w/ the vector)
+          */
+         int i = 0,rv;
+         while (i < nvecs) {
+             do {
+                 rv = fb->bfilter.write(fb, vec[i].iov_base, vec[i].iov_len);
+             } while (rv == -1 && (errno == EINTR || errno == EAGAIN)
+                      && !(fb->flags & B_EOUT));
+             if (rv == -1) {
+                 if (errno != EINTR && errno != EAGAIN) {
+                     doerror (fb, B_WR);
+                 }
+                 return -1;
+             }
+             fb->bytes_sent += rv;
+             /* recalculate vec to deal with partial writes */
+             while (rv > 0) {
+                 if (rv < vec[i].iov_len) {
+                     vec[i].iov_base = (char *)vec[i].iov_base + rv;
+                     vec[i].iov_len -= rv;
+                     rv = 0;
+                     if (vec[i].iov_len == 0) {
+                         ++i;
+                     }
+                 } else {
+                     rv -= vec[i].iov_len;
+                     ++i;
+                 }
+             }
+             if (fb->flags & B_EOUT)
+                 return -1;
+         }
+         /* if we got here, we wrote it all */
+         return 0;
+     } else {
+         return bwritev(fb->next,vec,nvecs);
+     }
+ }
+ -----
+ The default filter's writev function will pretty much like
+ writev_it_all.
+ 
+ 
+        Writing
+ 
+ The general case for writing data is significantly simpler with this
+ model.  Because special cases are not dealt with in the BUFF core,
+ a single internal interface to writing data is possible; I'm going
+ to assume it's reasonable to standardize on write_with_errors, but
+ some other function may be more appropriate.
+ 
+ In the revised bwrite (which I'll ommit for brievity), the following
+ must be done:
+        check for error conditions
+        check to see if any buffering is done; if not, send the data
+                directly to the write_with_errors function
+        check to see if we should use writev or write_with_errors
+                as above
+        copy the data to the buffer (we know it fits since we didn't
+                need writev or write_with_errors)
+ 
+ The other work the current bwrite is doing is
+        ifdef'ing around NO_WRITEV
+        numerous decisions regarding whether or not to send chunks
+ 
+ Generally, buff.c has a number of functions whose entire purpose is
+ to handle particular special cases wrt chunking, all of which could
+ be simplified with a chunking filter.
+ 
+ write_with_errors would not need to change; buff_write would.  Here
+ is a new version of it:
+ 
+ -----
+ /* the lowest level writing primitive */
+ static ap_inline int buff_write(BUFF *fb, const void *buf, int nbyte)
+ {
+     if (fb->bfilter.write)
+         return fb->bfilter.write(fb->next_writer,buff,nbyte);
+     else
+         return bwrite(fb->next_writer,buff,nbyte);
+ }
+ -----
+ 
+ If the btransmitfile function is called on a buffer which doesn't implement
+ it, the system will attempt to read data from the file identified
+ by the file_info_ptr structure and use other methods to write to it.
+ 
+        Reading
+ 
+ One of the basic reading functions in Apache 1.3b3 is buff_read;
+ here is how it would look within this spec:
+ 
+ -----
+ /* the lowest level reading primitive */
+ static ap_inline int buff_read(BUFF *fb, void *buf, int nbyte)
+ {
+     int rv;
+ 
+     if (!fb)
+         return -1; /* the bottom level filter is not set up properly */
+ 
+     if (fb->bfilter.read)
+         return fb->bfilter.read(fb->next_reader,buf,nbyte,fb->bfilter_info);
+     else
+         return bread(fb->next_reader,buff,nbyte);
+ }
+ -----
+ The code currently in buff_read would become part of the default
+ filter.
+ 
+ 
+        Flushing data
+ 
+ flush will get passed on down the stack automatically, with recursive
+ calls to bflush.  The user-supplied flush function will be called then,
+ and also before close is called.  The user-supplied flush should not
+ call flush on the next buffer.
+ 
+ [djg: Poorly written "expanding" filters can cause some nastiness
+ here.  In order to flush a layer you have to write out your current
+ buffer, and that may cause the layer below to overflow a buffer and
+ flush it.  If the filter is expanding then it may have to add more to
+ the buffer before flushing it to the layer below.  It's possible that
+ the layer below will end up having to flush twice.  It's a case where
+ writev-like capabilities are useful.]
+ 
+        Closing Stacks and Filters
+ 
+ When a filter is removed from the stack, flush will be called then close
+ will be called.  When the entire stack is being closed, this operation
+ will be done automatically on each filter within the stack; generally,
+ filters should not operate on other filters further down the stack,
+ except to pass data along when flush is called.
+ 
+        Flags and Options
+ 
+ Changes to flags and options using the current functions only affect
+ one buffer.  To affect all the buffers on down the chain, use
+ bsetstackopts or bsetstackflags.
+ 
+ bgetopt is currently only used to grab a count of the bytes sent;
+ it will continue to provide that functionality.  bgetflags is
+ used to provide information on whether or not the connection is
+ still open; it'll continue to provide that functionality as well.
+ 
+ The core BUFF operations will remain, though some operations which
+ are done via flags and options will be done by attaching appropriate
+ filters instead (eg. chunking).
+ 
+ [djg: I'd like to consider filesystem metadata as well -- we only need
+ a few bits of metadata to do HTTP: file size and last modified.  We
+ need an etag generation function, it is specific to the filters in
+ use.  You see, I'm envisioning a bottom layer which pulls data out of
+ a database rather than reading from a file.]
+ 
+ -------
+ 
+ This file is there so that I do not have to remind myself
+ about the reasons for Layered IO, apart from the obvious one.
+ 
+ 0. To get away from a 1 to 1 mapping
+ 
+    i.e. a single URI can cause multiple backend requests, 
+    in arbitrary configurations, such as in paralel, tunnel/piped, 
+    or in some sort of funnel mode. Such multiple backend
+    requests, with fully layered IO can be treated exactly
+    like any URI request; and recursion is born :-)
+ 
+ 1. To do on the fly charset conversion
+ 
+    Be, theoretically, be able to send out your content using
+    latin1, latin2 or any other charset; generated from static
+    _and_ dynamic content in other charsets (typically unicode
+    encoded as UTF7 or UTF8). Such conversion is prompted by
+    things like the user-agent string, a cookie, or other hints
+    about the capabilities of the OS, language preferences and
+    other (in)capabilities of the final receipient. 
+ 
+ 2. To be able to do fancy templates
+ 
+    Have your application/cgi sending out an XML structure of
+    field/value pair-ed contents; which is substituted into a 
+    template by the web server; possibly based on information 
+    accessible/known to the webserver which you do not want to 
+    be known to the backend script. Ideally that template would
+    be just as easy to generate by a backend as well (see 0).
+ 
+ 3. On the fly translation
+ 
+    And other general text and output mungling, such as translating
+    an english page in spanish whilst it goes through your Proxy,
+    or JPEG-ing a GIF generated by mod_perl+gd.
+ 
+ Dw.
+ ---------
+ 
+ From dgaudet@arctic.org Fri Feb 20 00:36:52 1998
+ Date: Fri, 20 Feb 1998 00:35:37 -0800 (PST)
+ From: Dean Gaudet <dgaudet@arctic.org>
+ To: new-httpd@apache.org
+ Subject: page-based i/o
+ X-Comment: Visit http://www.arctic.org/~dgaudet/legal for information regarding copyright and disclaimer.
+ Reply-To: new-httpd@apache.org
+ 
+ Ed asked me for more details on what I mean when I talk about "paged based
+ zero copy i/o". 
+ 
+ While writing mod_mmap_static I was thinking about the primitives that the
+ core requires of the filesystem.  What exactly is it that ties us into the
+ filesystem?  and how would we abstract it?  The metadata (last modified
+ time, file length) is actually pretty easy to abstract.  It's also easy to
+ define an "index" function so that MultiViews and such can be implemented. 
+ And with layered I/O we can hide the actual details of how you access
+ these "virtual" files. 
+ 
+ But therein lies an inefficiency.  If we had only bread() for reading
+ virtual files, then we would enforce at least one copy of the data. 
+ bread() supplies the place that the caller wants to see the data, and so
+ the bread() code has to copy it.  But there's very little reason that
+ bread() callers have to supply the buffer... bread() itself could supply
+ the buffer.  Call this new interface page_read().  It looks something like
+ this:
+ 
+     typedef struct {
+        const void *data;
+        size_t data_len; /* amt of data on page which is valid */
+        ... other stuff necessary for managing the page pool ...
+     } a_page_head;
+ 
+     /* returns NULL if an error or EOF occurs, on EOF errno will be
+      * set to 0
+      */
+     a_page_head *page_read(BUFF *fb);
+ 
+     /* queues entire page for writing, returns 0 on success, -1 on
+      * error
+      */
+     int page_write(BUFF *fb, a_page_head *);
+ 
+ It's very important that a_page_head structures point to the data page
+ rather than be part of the data page.  This way we can build a_page_head
+ structures which refer to parts of mmap()d memory.
+ 
+ This stuff is a little more tricky to do, but is a big win for performance.
+ With this integrated into our layered I/O it means that we can have
+ zero-copy performance while still getting the advantages of layering.
+ 
+ But note I'm glossing over a bunch of details... like the fact that we
+ have to decide if a_page_heads are shared data, and hence need reference
+ counting (i.e. I said "queues for writing" up there, which means some
+ bit of the a_page_head data has to be kept until its actually written).
+ Similarly for the page data.
+ 
+ There are other tricks in this area that we can take advantage of --
+ like interprocess communication on architectures that do page flipping.
+ On these boxes if you write() something that's page-aligned and page-sized
+ to a pipe or unix socket, and the other end read()s into a page-aligned
+ page-sized buffer then the kernel can get away without copying any data.
+ It just marks the two pages as shared copy-on-write, and only when
+ they're written to will the copy be made.  So to make this work, your
+ writer uses a ring of 2+ page-aligned/sized buffers so that it's not
+ writing on something the reader is still reading.
+ 
+ Dean
+ 
+ ----
+ 
+ For details on HPUX and avoiding extra data copies, see
+ <ftp://ftp.cup.hp.com/dist/networking/briefs/copyavoid.pdf>.
+ 
+ (note that if you get the postscript version instead, you have to 
+ manually edit it to remove the front page before any version of 
+ ghostscript that I have used will read it)
+ 
+ ----
+ 
+ I've been told by an engineer in Sun's TCP/IP group that zero-copy TCP
+ in Solaris 2.6 occurs when:
+ 
+     - you've got the right interface card (OC-12 ATM card I think)
+     - you use write()
+     - your write buffer is 16k aligned and a multiple of 16k in size
+ 
+ We currently get the 16k stuff for free by using mmap().  But sun's
+ current code isn't smart enough to deal with our initial writev()
+ of the headers and first part of the response.
+ 
+ ----
+ 
+ Systems that have a system call to efficiently send the contents of a 
+ descriptor across the network.  This is probably the single best way
+ to do static content on systems that support it.
+ 
+ HPUX: (10.30 and on)
+ 
+       ssize_t sendfile(int s, int fd, off_t offset, size_t nbytes,
+               const struct iovec *hdtrl, int flags);
+ 
+       (allows you to add headers and trailers in the form of iovec
+       structs)  Marc has a man page; ask if you want a copy.  Not included
+       due to copyright issues.  man page also available from 
+       http://docs.hp.com/ (in particular, 
+       http://docs.hp.com:80/dynaweb/hpux11/hpuxen1a/rvl3en1a/@Generic__BookTextView/59894;td=3 )
+ 
+ Windows NT:
+ 
+        BOOL TransmitFile(     SOCKET hSocket, 
+            HANDLE hFile, 
+            DWORD nNumberOfBytesToWrite, 
+            DWORD nNumberOfBytesPerSend, 
+            LPOVERLAPPED lpOverlapped, 
+            LPTRANSMIT_FILE_BUFFERS lpTransmitBuffers, 
+            DWORD dwFlags 
+           ); 
+ 
+        (does it start from the current position in the handle?  I would
+        hope so, or else it is pretty dumb.)
+ 
+        lpTransmitBuffers allows for headers and trailers.
+ 
+        Documentation at:
+ 
+        http://premium.microsoft.com/msdn/library/sdkdoc/wsapiref_3pwy.htm
+        http://premium.microsoft.com/msdn/library/conf/html/sa8ff.htm
+ 
+        Even less related to page based IO: just context switching:
+        AcceptEx does an accept(), and returns the start of the
+        input data.  see:
+ 
+        http://premium.microsoft.com/msdn/library/sdkdoc/pdnds/sock2/wsapiref_17jm.htm
+ 
+        What this means is you require one less syscall to do a
+        typical request, especially if you have a cache of handles
+        so you don't have to do an open or close.  Hmm.  Interesting
+        question: then, if TransmitFile starts from the current
+        position, you need a mutex around the seek and the
+        TransmitFile.  If not, you are just limited (eg. byte
+        ranges) in what you can use it for.
+ 
+        Also note that TransmitFile can specify TF_REUSE_SOCKET, so that
+        after use the same socket handle can be passed to AcceptEx.  
+        Obviously only good where we don't have a persistent connection
+        to worry about.
+ 
+ ----
+ 
+ Note that all this is shot to bloody hell by HTTP-NG's multiplexing.
+ If fragment sizes are big enough, it could still be worthwhile to
+ do copy avoidence.  It also causes performance issues because of
+ its credit system that limits how much you can write in a single
+ chunk.
+ 
+ Don't tell me that if HTTP-NG becomes popular we will seen vendors 
+ embedding SMUX (or whatever multiplexing is used) in the kernel to
+ get around this stuff.  There we go, Apache with a loadable kernel
+ module.  
+ 
+ ----
+ 
+ Larry McVoy's document for SGI regarding sendfile/TransmitFile:
+ ftp://ftp.bitmover.com/pub/splice.ps.gz
+ From dgaudet@arctic.org Sun Jun 20 11:07:58 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: dgaudet@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: mpm update
+ Date: 19 Jun 1999 07:17:00 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 104
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.3.96dg4.990618172933.27639Y-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 929769420 64417 141.1.129.1 (19 Jun 1999 05:17:00 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 19 Jun 1999 05:17:00 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:31056
+ 
+ I imported mpm-3 into the apache-2.0 repository (tag mpm-3 if you want
+ it).
+ 
+ Then I threw in a bunch of my recent email ramblings, because I'm getting
+ tired of repeating them, mostly off-list to folks who ask "why doesn't
+ apache do XYZ?"  I intend to be more proactive in this area, because it
+ can only help. 
+ 
+ Then I ripped up BUFF and broke lots of stuff and put in a first crack at
+ layering.  Info on that below.
+ 
+ If you check out the tree, and build it (using Configuration.mpm) you
+ should be able to serve up the top page of the manual, that's all I've
+ tested so far ;) 
+ 
+ Dean
+ 
+ goals? we need an i/o abstraction which has these properties:
+ 
+ - buffered and non-buffered modes
+ 
+     The buffered mode should look like FILE *.
+ 
+     The non-buffered mode should look more like read(2)/write(2).
+ 
+ - blocking and non-blocking modes
+ 
+     The blocking mode is the "easy" mode -- it's what most module writers
+     will see.  The non-blocking mode is the "hard" mode, this is where
+     module writers wanting to squeeze out some speed will have to play.
+     In order to build async/sync hybrid models we need the
+     non-blocking i/o abstraction.
+ 
+ - timed reads and writes (for blocking cases)
+ 
+     This is part of my jihad against asynchronous notification.
+ 
+ - i/o filtering or layering
+ 
+     Yet another Holy Grail of computing.  But I digress.  These are
+     hard when you take into consideration non-blocking i/o -- you have
+     to keep lots of state.  I expect our core filters will all support
+     non-blocking i/o, well at least the ones I need to make sure we kick
+     ass on benchmarks.  A filter can deny a switch to non-blocking mode,
+     the server will have to recover gracefully (ha).
+ 
+ - copy-avoidance
+ 
+     Hey what about zero copy a la IO-Lite?  After having experienced it
+     in a production setting I'm no longer convinced of its benefits.
+     There is an enormous amount of overhead keeping lists of buffers,
+     and reference counts, and cleanup functions, and such which requires
+     a lot of tuning to get right.  I think there may be something here,
+     but it's not a cakewalk.
+ 
+     What I do know is that the heuristics I put into apache-1.3 to choose
+     writev() at times are almost as good as what you can get from doing
+     full zero-copy in the cases we *currently* care about.  To put it
+     another way, let's wait another generation to deal with zero copy.
+ 
+     But sendfile/transmitfile/etc. those are still interesting.
+ 
+     So instead of listing "zero copy" as a property, I'll list
+     "copy-avoidance".
+ 
+ So far?
+ 
+ - ap_bungetc added
+ - ap_blookc changed to return the character, rather than take a char *buff
+ - in theory, errno is always useful on return from a BUFF routine
+ - ap_bhalfduplex, B_SAFEREAD will be re-implemented using a layer I think
+ - chunking gone for now, will return as a layer
+ - ebcdic gone for now... it should be a layer
+ 
+ - ap_iol.h defined, first crack at the layers...
+ 
+     Step back a second to think on it.  Much like we have fread(3)
+     and read(2), I've got a BUFF and an ap_iol abstraction.  An ap_iol
+     could use a BUFF if it requires some form of buffering, but many
+     won't require buffering... or can do a better job themselves.
+ 
+     Consider filters such as:
+        - ebcdic -> ascii
+        - encryption
+        - compression
+     These all share the property that no matter what, they're going to make
+     an extra copy of the data.  In some cases they can do it in place (read)
+     or into a fixed buffer... in most cases their buffering requirements
+     are different than what BUFF offers.
+ 
+     Consider a filter such as chunking.  This could actually use the writev
+     method to get its job done... depends on the chunks being used.  This
+     is where zero-copy would be really nice, but we can get by with a few
+     heuristics.
+ 
+     At any rate -- the NSPR folks didn't see any reason to included a
+     buffered i/o abstraction on top of their layered i/o abstraction... so
+     I feel like I'm not the only one who's thinking this way.
+ 
+ - iol_unix.c implemented... should hold us for a bit
+ 
+ 
+ 
+ 


ossp-pkg/sio/BRAINSTORM/asf-ideas.txt -> 1.1

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+ From manoj@io.com Wed Aug 16 21:38:14 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-7115-rse+apache=en.muc.de
+ From: manoj@io.com (Manoj Kasichainula)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: My proposal for buckets/filtering in 3.0.
+ Date: 14 Aug 2000 18:59:14 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 137
+ Approved: postmaster@m2ndom
+ Message-ID: <20000814050814.A16555@manojk.users.mindspring.com>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 966272354 36734 141.1.129.1 (14 Aug 2000 16:59:14 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 14 Aug 2000 16:59:14 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:41295
+ 
+ This is quite different than the other proposals. From the feedback I
+ got during the meeting, this isn't suitable for Apache 2.0 because
+ it's still not developed enough (it popped into my head *during* the
+ meeting after all) and it requires more rewriting of existing modules
+ than the current 2.0 filtering scheme. I agree with the sentiment that
+ says to get 2.0 out soon rather than adding more features, so I agree.
+ 
+ Also, I have a bad feeling someone else already put forward this idea.
+ But, I'll send it out anyway.
+ 
+ The main difference between this design and the others is that there
+ are more buckets and fewer filters.
+ 
+ Filters are things that talk to the network, and they are two-way. SSL
+ and chunking are filters. They don't change very much in this case; as
+ is the case now, they are just iols that can handle buckets.
+ 
+ Most everything else is a bucket in this case. Actually, they are
+ probably better described as matrushka dolls or those little nested
+ plastic barrels. In fact, I'll call them barrels to increase
+ confusion.
+ 
+ Brigades don't exist in this scheme. They are just compound barrels.
+ 
+ I think that each barrel will have a URI-identifier. This is useful
+ for caching.
+ 
+ Content-manipulating filters in the other designs are barrels in this
+ one. Also, while they were "writers" in the other designs, they are
+ "readers" in this one. So instead of a push-style design where filters
+ are written to by other filters, this scheme has barrels reading from
+ other barrels.
+ 
+ So here's how a request would proceed:
+ 
+ - HTTP request comes in, munched on by various filters, and passed to
+   the request handler.
+ 
+ - request handler picks out the URI that was requested, creates a URI
+   barrel initialized to that URI, and reads the content and metadata
+   out of it.
+   ("ap_create_uri_barrel("http://www.deedee.com/dancing/",
+   barrel_types)->read();")
+ 
+ - The URI barrel, when created, figures out how the content should be
+   delivered, and creates subbarrels to deal with them. I'll give three
+   cases:
+ 
+   Case #1: A file on the disk
+   Case #2: A cgi script that outputs postscript that gets interpreted
+   into a PNG image file
+   Case #3: a proxy request
+ 
+   In case #1, the URI barrel figures out that it's accessing a file,
+   creates a filehandle barrel, and then binds its own content-handling
+   calls to the filehandle barrel.
+ 
+   file -> uri -> HTTP handler
+ 
+   In case #2, the URI barrel creates a CGI barrel that is initialized
+   with a file barrel pointing to the CGI script. Then uri_barrel
+   creates a postscript barrel initialized with the CGI barrel and the
+   parameter "PNG". The URI barrel then binds its content-handling
+   calls to the postscript barrel.
+ 
+   CGI script file -> mod_cgi -> mod_postscript -> uri -> HTTP handler
+ 
+   In case #3, the URI barrel figures out that this is a remote request
+   and creates an HTTP client barrel. The URI barrel then binds its
+   conent requst handler to the HTTP barrel. Maybe there needs to be an
+   intervening proxy barrel, or maybe the URI barrel knows proxy
+   semantics, or maybe the request handler needs smarts about HTTP
+   proxies. I'm not in touch with HTTP/1.1 proxying enough to know.
+ 
+   HTTP client -> uri -> HTTP server handler
+   
+ - The request handler gets barrels back, and using the appropriate
+   barrel functions, writes their headers and data through the filters
+   back to the client.
+ 
+ When anything creates a barrel, it passes in:
+ 
+ - a pool to allocate memory from. The stuff read from the barrel must
+   be in the scope of that pool.
+ - a list of capabilities that are required, and a list of preferred
+   capabilities. capabilities include: "send-from-file-descriptor",
+   "send from memory", "write-to-content", and so on.
+ 
+   This feels like content negotation, which scares me. But, very
+   little of it is actually necessary in a first pass. A single
+   "memory-block" capability is all that's mandatory, really.
+   Everything else is extra features and optimization.
+ 
+ The barrel bring created will then attempt to meet those wishes if
+ possible, or return an error.
+ 
+ This is really not mapped out well-enough, and needs code, which will
+ wait until Apache 3.0 development starts up. But, here are the cool
+ features I can imagine:
+ 
+ - non-blocking I/O can be a capability of a barrel. One API of the
+   barrel would be to return the file descriptor (or "event") it is
+   waiting for, so that it can be selected on, and a full event-based
+   server should be possible. When some barrel three levels deep
+   doesn't support non-blocking I/O, the request handler can decide to
+   punt to a seperate thread. This way, different programming models
+   for modules can be supported. 
+ 
+ - Writability would be another capability. If a barrel is writable,
+   that URI is available to DAV.
+ 
+ - Set-asides and lifetime of data aren't that much of an issue anymore
+   (or at least I haven't thought of a case where they are). Barrels
+   are naturally kept around only as long as they are needed, since
+   their scope is determined by the consumer of the barrel. Caching is
+   done with a cacher barrel that uses a large-scoped pool, for example.
+ 
+ - This scheme allows not just chains of barrels, but trees. So half of
+   a document can come from PHP and half can come from SSI. You just
+   need a container barrel that knows what parts are interpreted by
+   what modules. There could be an MS-Word barrel that munches on
+   multiple HTTP requests for HTML + images. This scares me.
+ 
+ - Because of the content-negotiation features, a barrel can always
+   figure out what the optimal format for sending content back should
+   be.
+ 
+ - subrequests are really easy (thanks for the idea of URI barrels,
+   Ryan) 
+ 
+ - Should allow "magic cache" like was discussed back at the June/July
+   '98 meeting. In fact, it should be really easy.
+ 
+ There are plenty of unanswered questions here, such as how metadata
+ will work, how exactly proxies fit into this, and how things like DAV
+ collections fit in. But I'm sleepy.
+ 
+ From fielding@kiwi.ICS.UCI.EDU Wed Aug 16 21:39:15 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-7124-rse+apache=en.muc.de
+ From: fielding@kiwi.ICS.UCI.EDU ("Roy T. Fielding")
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: My proposal for buckets/filtering in 3.0.
+ Date: 15 Aug 2000 07:00:31 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 155
+ Approved: postmaster@m2ndom
+ Message-ID: <200008141352.aa13983@gremlin-relay.ics.uci.edu>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 966315631 57145 141.1.129.1 (15 Aug 2000 05:00:31 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 15 Aug 2000 05:00:31 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:41304
+ 
+ >Most everything else is a bucket in this case. Actually, they are
+ >probably better described as matrushka dolls or those little nested
+ >plastic barrels. In fact, I'll call them barrels to increase
+ >confusion.
+ 
+ Hah, cute, but how is it different than our current subrequests?
+ 
+ >I think that each barrel will have a URI-identifier. This is useful
+ >for caching.
+ 
+ Yes.  We would also need to name the handlers that define how a
+ barrel is constructed for a given request-URI.
+ 
+ >Content-manipulating filters in the other designs are barrels in this
+ >one. Also, while they were "writers" in the other designs, they are
+ >"readers" in this one. So instead of a push-style design where filters
+ >are written to by other filters, this scheme has barrels reading from
+ >other barrels.
+ >
+ >So here's how a request would proceed:
+ >
+ >- HTTP request comes in, munched on by various filters, and passed to
+ >  the request handler.
+ >
+ >- request handler picks out the URI that was requested, creates a URI
+ >  barrel initialized to that URI, and reads the content and metadata
+ >  out of it.
+ >  ("ap_create_uri_barrel("http://www.deedee.com/dancing/",
+ >  barrel_types)->read();")
+ >
+ >- The URI barrel, when created, figures out how the content should be
+ >  delivered, and creates subbarrels to deal with them. I'll give three
+ >  cases:
+ >
+ >  Case #1: A file on the disk
+ >  Case #2: A cgi script that outputs postscript that gets interpreted
+ >  into a PNG image file
+ >  Case #3: a proxy request
+ >
+ >  In case #1, the URI barrel figures out that it's accessing a file,
+ >  creates a filehandle barrel, and then binds its own content-handling
+ >  calls to the filehandle barrel.
+ >
+ >  file -> uri -> HTTP handler
+ >
+ >  In case #2, the URI barrel creates a CGI barrel that is initialized
+ >  with a file barrel pointing to the CGI script. Then uri_barrel
+ >  creates a postscript barrel initialized with the CGI barrel and the
+ >  parameter "PNG". The URI barrel then binds its content-handling
+ >  calls to the postscript barrel.
+ >
+ >  CGI script file -> mod_cgi -> mod_postscript -> uri -> HTTP handler
+ >
+ >  In case #3, the URI barrel figures out that this is a remote request
+ >  and creates an HTTP client barrel. The URI barrel then binds its
+ >  conent requst handler to the HTTP barrel. Maybe there needs to be an
+ >  intervening proxy barrel, or maybe the URI barrel knows proxy
+ >  semantics, or maybe the request handler needs smarts about HTTP
+ >  proxies. I'm not in touch with HTTP/1.1 proxying enough to know.
+ >
+ >  HTTP client -> uri -> HTTP server handler
+ >  
+ >- The request handler gets barrels back, and using the appropriate
+ >  barrel functions, writes their headers and data through the filters
+ >  back to the client.
+ 
+ Yep, subrequests.
+ 
+ >When anything creates a barrel, it passes in:
+ >
+ >- a pool to allocate memory from. The stuff read from the barrel must
+ >  be in the scope of that pool.
+ >- a list of capabilities that are required, and a list of preferred
+ >  capabilities. capabilities include: "send-from-file-descriptor",
+ >  "send from memory", "write-to-content", and so on.
+ >
+ >  This feels like content negotation, which scares me. But, very
+ >  little of it is actually necessary in a first pass. A single
+ >  "memory-block" capability is all that's mandatory, really.
+ >  Everything else is extra features and optimization.
+ 
+ Hmmm, sorry, I think I've heard that phrase one too many times this
+ past week.  Figure out what the architectural context is -- all of the
+ forces that will impact this design in terms of the application needs.
+ When you have covered all of that, everything else is extra features
+ and optimization.  Things like single-copy IO and sendfile support are
+ not optimizations -- they are the requirements that motivate our next
+ generation architecture.
+ 
+ >The barrel bring created will then attempt to meet those wishes if
+ >possible, or return an error.
+ 
+ Hmmm, that sounds like magic to me.  The whole point of bucket brigades
+ was to specify that magic in a way that can be standard for all modules.
+ 
+ >This is really not mapped out well-enough, and needs code, which will
+ >wait until Apache 3.0 development starts up. But, here are the cool
+ >features I can imagine:
+ >
+ >- non-blocking I/O can be a capability of a barrel. One API of the
+ >  barrel would be to return the file descriptor (or "event") it is
+ >  waiting for, so that it can be selected on, and a full event-based
+ >  server should be possible. When some barrel three levels deep
+ >  doesn't support non-blocking I/O, the request handler can decide to
+ >  punt to a seperate thread. This way, different programming models
+ >  for modules can be supported. 
+ 
+ It does mean that something has to read from the barrel and write to
+ the network, right?  Or is this a model where we give the network to
+ the barrel and it writes?  Kind of hard top manage the latter.
+ 
+ >- Writability would be another capability. If a barrel is writable,
+ >  that URI is available to DAV.
+ 
+ Yes, all source resources should be available to DAV.  The way to do that
+ is to asign them URI and pass their identifiers as metadata.  Let the
+ protocol filter decide what to do with that information.
+ 
+ >- Set-asides and lifetime of data aren't that much of an issue anymore
+ >  (or at least I haven't thought of a case where they are). Barrels
+ >  are naturally kept around only as long as they are needed, since
+ >  their scope is determined by the consumer of the barrel. Caching is
+ >  done with a cacher barrel that uses a large-scoped pool, for example.
+ 
+ Right, just like the 1.3 subrequest architecture.
+ 
+ >- This scheme allows not just chains of barrels, but trees. So half of
+ >  a document can come from PHP and half can come from SSI. You just
+ >  need a container barrel that knows what parts are interpreted by
+ >  what modules. There could be an MS-Word barrel that munches on
+ >  multiple HTTP requests for HTML + images. This scares me.
+ 
+ It should.  Keep in mind that all of the sources would have to pass
+ through the access control steps.
+ 
+ >- Because of the content-negotiation features, a barrel can always
+ >  figure out what the optimal format for sending content back should
+ >  be.
+ 
+ You mean every barrel will have to know everything about the request,
+ including things like HTTP negotiation?  Yikes.
+ 
+ >- subrequests are really easy (thanks for the idea of URI barrels,
+ >  Ryan) 
+ 
+ I don't see much difference from 1.3 subrequests.
+ 
+ >- Should allow "magic cache" like was discussed back at the June/July
+ >  '98 meeting. In fact, it should be really easy.
+ 
+ Easy to identify cacheable items, yes, but how easy is it for the
+ cache manager to manage overall allocations and reap old entries?
+ 
+ ....Roy
+ 


ossp-pkg/sio/BRAINSTORM/brustoloni-abs.txt -> 1.1

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+ Copy avoidance in networked file systems
+ ----------------------------------------
+ 
+   Jose' Carlos Brustoloni
+   Bell Labs, Lucent Technologies
+   jcb@research.bell-labs.com
+ 
+ The point-to-point bandwidth of gigabit networks can surpass
+ the main memory copy bandwidth of many current hosts. Therefore,
+ researchers have been devoting considerable attention to the problem
+ of copy avoidance in network I/O. In particular, a recent study shows
+ that copying can be avoided without modifying the semantics of existing
+ networking APIs [1].
+ 
+ In contrast, far less attention has been recently devoted to copy
+ avoidance in file I/O. This neglect may be motivated by several
+ subtle misperceptions:
+ 
+ 1) Disks are far slower than main memory (or gigabit networks).
+ 
+    This is indeed true, but copy avoidance can still be worthwhile
+    in file I/O because:
+    (a) copy avoidance can reduce CPU utilization and significantly
+        improve the throughput of file servers, which often are CPU-bound, and
+    (b) caching can avoid physical disk I/O and greatly speed up file systems.
+ 
+ 2) Many copy avoidance techniques for network I/O are not useful in file I/O.
+ 
+    Indeed, copy avoidance techniques for network I/O
+    often exploit the fact that buffers are ephemeral, i.e. are
+    deallocated as soon as processing of the corresponding input or
+    output request completes. On the contrary, buffers used in file I/O
+    often are cached. For example, emulated copy [1] is a copy avoidance
+    scheme for network I/O that uses input alignment and page swapping
+    on input and TCOW, a form of copy-on-write, on output. If used on
+    file input, page swapping would corrupt the file system cache
+    with the previous contents of the client input buffers.
+    If used on file output, TCOW would allow cached output pages to
+    be corrupted because, after output completes, the output reference
+    is lost and therefore the pages can be overwritten or reused.
+ 
+    This does not mean, however, that copy avoidance is unattainable
+    in file I/O. Systems usually also offer mapped file I/O,
+    which allows file data to be passed between applications and the
+    operating system by page mapping and unmapping. Mapped files are a practical
+    solution that is already widely available for copy avoidance in file I/O.
+ 
+ 3) Copying between mapped files and network I/O buffers can be unavoidable
+    because of page alignment constraints.
+ 
+    For example, in a networked file server, data may be received from
+    the network for output to the file system. The data will usually be
+    preceded by an application-layer header specifying the file and
+    offset from the beginning of the file (for simplicity, let us assume
+    that the offset is multiple of the page size). This header can make
+    copy avoidance difficult because (a) the application must read the
+    header to determine the file and (b) the header may make the following data
+    arbitrarily aligned, whereas data must be page-aligned for mapped file I/O.
+ 
+    However, I show that:
+ 
+    (a) If the network adapter supports system-aligned buffering
+        (early demultiplexing or buffer snap-off) [2], then the application
+        can peek at the header and, after decoding it, input the data
+        directly to the correct mapped file region, using emulated copy.
+        Data is passed between network and file system with copy avoidance
+        and without any modifications in existing APIs.
+ 
+    (b) Even without such adapter support, copy avoidance is possible with
+        header patching, a novel software optimization.
+ 
+        Let h' be the preferred alignment for input from the network (usually
+        equal to the length of any unstripped protocol headers below the
+        application layer), h be the length of the application-layer header,
+        and l be the data length (less than or equal to the network's
+        maximum transmission unit minus the lengths of headers at network
+        or higher layers). h' must be fixed and known by both sender and
+        receiver. On the contrary, h and l may vary from packet to packet.
+        Using header patching, the sender transmits the application-layer
+        header followed by the data starting at file offset o + h' + h
+        and of length l - h' - h, followed by data starting at file offset
+        o and of length h' + h (to achieve this out-of-order transmission,
+        the sender may use, e.g., Unix's writev call with a gather list).
+        The receiver peeks at the first h bytes of the input
+        (using, e.g., Unix's recv with MSG_PEEK flag),
+        decodes the application-layer header, and determines the address a
+        corresponding to file offset o (multiple of the page size)
+        in the correct mapped file region. The receiver then inputs l - h'
+        bytes to address a + h', followed by h' + h bytes to address a.
+        This causes most of the data to be passed by page swapping, after which
+        the data corresponding to offset o and of length h' + h is
+        patched on top of the application- and lower-layer
+        headers at address a.  After patching, the input buffer starts at
+        the correct offset in the mapped file region and runs uninterrupted
+        for length l with the data in correct order, as illustrated by the
+        following figure.
+ 
+                       +----+---+----------+----+
+         Packet:       | h' | h |    d1    | d0 |
+                       +----+---+----------+----+
+ 
+         Pooled NW     +----+---+----------+      +----+--------------+
+         buffers:      | h' | h |    d1    |      | d0 |              |
+                       +----+---+----------+      +----+--------------+
+                       |    |
+               reverse | ^  |      ^                |
+               copyout | |  |      | swap           |
+                       |    |      v                |
+         Mapped        +----+---+----------+        |
+         file:         |    | h |    d1    |        |
+                       +----+---+----------+        |
+                       \--------/                   |
+                            ^                       |
+                            |                       |
+                     patch  +-----------------------+
+ 
+ My experiments on the Credit Net ATM network at 512 Mbps show that
+ copy avoidance can substantially improve the performance of networked
+ file systems. Because of cache effects, copy avoidance benefits are
+ synergistic: Greatest benefits are obtained when copying is avoided on the
+ entire end-to-end data path, including network and file I/O.
+ Additionally, the experiments confirm each of the above claims.
+ 
+ References
+ ----------
+ 
+ [1] J. Brustoloni and P. Steenkiste. ``Effects of Buffering
+     Semantics on I/O performance'', in Proc. OSDI'96,
+     USENIX, Oct. 1996, pp. 277-291. Also available from
+     http://www.cs.cmu.edu/~jcb/.
+ 
+ [2] J. Brustoloni and P. Steenkiste. ``Copy Emulation in
+     Checksummed, Multiple-Packet Communication'', in
+     Proc. INFOCOM'97, IEEE, April 1997. Also available from
+     http://www.cs.cmu.edu/~jcb/.
+ 
+ ---------------------------------------------------------------------------
+ 
+ Work performed while at the School of Computer Science,
+ Carnegie Mellon University.
+ To be presented at Gigabit Networking Workshop - GBN'98.


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+ http://www.ccrc.wustl.edu/pub/ieee-tcgn/conference/gbn98/brustoloni-abs.html


ossp-pkg/sio/BRAINSTORM/c10k.html -> 1.1

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+ <html>
+ <head>
+ <title>The C10K problem</title>
+ </head>
+ <body>
+ <h1>The C10K problem</h1>
+ It's time for web servers to handle ten thousand clients simultaneously,
+ don't you think?  After all, the web is a big place now. 
+ <p>
+ And computers are big, too.  You can buy a 500MHz machine
+ with 1 gigabyte of RAM and six 100Mbit/sec Ethernet card for $3000 or so.  
+ Let's see - at 10000 clients, that's
+ 50KHz, 100Kbytes, and 60Kbits/sec per client.  
+ It shouldn't take any more horsepower than that to take four kilobytes 
+ from the disk and send them to the network once a second for each
+ of ten thousand clients.
+ (That works out to $0.30 per client, by the way.  Those
+ $100/client licensing fees some operating systems charge are starting to 
+ look a little heavy!)  So hardware is no longer the bottleneck.
+ <p>
+ One of the busiest ftp sites, ftp.cdrom.com, serves (as of May 1999)
+ around 5000 clients simultaneously through a 70 megabit/second pipe.
+ Pipes this fast aren't common yet, but technology is improving rapidly.
+ <p>
+ With that in mind, here are a few notes on how to configure operating 
+ systems and write code to support thousands of clients.  The discussion
+ centers around Unix-like operating systems, for obvious reasons.
+ 
+ <h2>I/O Strategies</h2>
+ There seem to be four ways of writing a fast web server to handle many
+ clients:
+ <ol>
+ <li>serve many clients with each server process or thread, and use
+ select() or poll() to avoid blocking.  This is the traditional favorite,
+ and is sometimes referred to as "using nonblocking I/O".
+ <li>serve many clients with each server process or thread, and use
+ asynchronous I/O to avoid blocking.  This has not yet become popular,
+ possibly because of poorly designed asynchronous I/O interfaces.
+ Zach Brown (author of HoserFTPD) thinks this might now be the way to go
+ for highest performance; see 
+ <a href="sigio.txt">his 14 April 1999 post to hftpd-users</a>.
+ <br>
+ There are several flavors of asynchronous I/O: 
+ <ul>
+ <li><a href="http://www.opengroup.org/onlinepubs/007908799/xsh/realtime.html">the aio_ interface</a>
+ (scroll down from that link to "Asynchronous input and output"), 
+ which associates a signal and value with each I/O operation.
+ Signals and their values are queued and delivered efficiently to the user process.
+ This is from the POSIX 1003.1b realtime extensions, and is also in the Single Unix Specification,
+ version 2, and in glibc 2.1.
+ <li>
+ <a href="http://www.dejanews.com/getdoc.xp?AN=410413704">F_SETSIG</a>
+ (see also <a href="http://www.dejanews.com/getdoc.xp?AN=366163395">here</a>),
+ which associates a signal with each file descriptor.
+ When a normal I/O function like read() or write() completes, the signal
+ is raised, with the file descriptor as an argument.  Similar to aio_ but
+ without the new calls, and slightly less flexible (you know the handle,
+ but you don't know whether it is ready for read() or for write() without
+ doing a poll() on it).
+ (Currently only in Linux, I think.)
+ <li>SIGIO (see <a href="http://www.delorie.com/gnu/docs/glibc/libc_147.html">glibc doc</a> or
+ <a href="http://www-users.cs.umn.edu/~bentlema/unix/BSD-UNIX:SysCalls_and_IPC.html">BSD Sockets doc</a>)
+ -- doesn't tell you which handle needs servicing, so it seems kind of coarse.
+ Used by the Linux F_SETSIG/aio_ implementation as a fallback when the realtime signal 
+ queue overflows.  
+ <a href="http://www.linuxhq.com/lnxlists/linux-kernel/lk_9905_01/msg00973.html">Here's
+ an example of its use</a>.  (Was partly broken in Linux kernels 2.2.0 - 2.2.7, fixed in 2.2.8.)
+ </ul>
+ <li>serve one client with each server thread, and let read() and write()
+ block.  (This is the only model supported by Java.)
+ <li>Build the server code into the kernel.  
+ Novell and Microsoft are both said to have done this at various times, and at least one NFS implementation does this.
+ IBM and Sun are said to have released specweb benchmark results using this technique.  
+ </ol>
+ <p>
+ Richard Gooch has written <a href="http://www.atnf.csiro.au/~rgooch/linux/docs/io-events.html">a paper discussing these options</a>.  Interesting reading.  
+ <p>
+ The Apache mailing lists have some interesting posts 
+ (<a href="http://www.humanfactor.com/cgi-bin/cgi-delegate/apache-ML/nh/1999/March/1st-half/0143.html">one</a>,
+ <a href="http://www.humanfactor.com/cgi-bin/cgi-delegate/apache-ML/nh/1999/March/2nd-half/0007.html">two</a>,
+ <a href="http://www.humanfactor.com/cgi-bin/cgi-delegate/apache-ML/nh/1999/March/2nd-half/0009.html">three</a>)
+ about why they prefer not to use select() (basically, they think that makes plugins harder).   
+ <br>
+ I have not yet seen any data comparing the performance of the four approaches.
+ <p>
+ Mark Russinovich wrote 
+ <a href="http://linuxtoday.com/stories/5499.html">an editorial</a> and
+ <a href="http://winntmag.com/Magazine/Article.cfm?ArticleID=5048">an article</a>
+ discussing I/O strategy issues in the 2.2 Linux kernel.  Worth reading, even
+ he seems misinformed on some points.  In particular, he
+ seems to think that Linux 2.2's asyncrhonous I/O 
+ (see F_SETSIG above) doesn't notify the user process when data is ready, only
+ when new connections arrive.  This seems like a bizarre misunderstanding.
+ See also 
+ <a href="http://www.dejanews.com/getdoc.xp?AN=431444525">comments on an earlier draft</a>,
+ <a href="http://www.dejanews.com/getdoc.xp?AN=472893693">a rebuttal</a> from Mingo, 
+ <a href="http://www.linuxhq.com/lnxlists/linux-kernel/lk_9905_01/msg00089.html">Russinovich's comments of 2 May 1999</a>,
+ <a href="http://www.linuxhq.com/lnxlists/linux-kernel/lk_9905_01/msg00263.html">a rebuttal</a> from Alan Cox,
+ and various 
+ <a href="http://www.dejanews.com/dnquery.xp?ST=PS&QRY=threads&DBS=1&format=threaded&showsort=score&maxhits=100&LNG=ALL&groups=fa.linux.kernel+&fromdate=jun+1+1998">posts to linux-kernel</a>.  
+ 
+ <h2>Limits on open filehandles</h2>
+ <ul>
+ <li>Solaris: see <a
+ href="http://www.wins.uva.nl/pub/solaris/solaris2/Q3.45.html">the Solaris FAQ,
+ question 3.45</a>.
+ <li>FreeBSD: use <tt>sysctl -w kern.maxfiles=nnnn</tt> to raise limit
+ <li>Linux: Even the 2.2.5 kernel limits the number of open files to 1024.
+ I believe the AC series of patches remove this limit; see <a href="http://kernel.org">ftp.*.kernel.org/pub/linux/kernel/alan/</a>
+ for mirrors of e.g. ftp://ftp.linux.org.uk/pub/linux/alan/2.2/patch-2.2.5-ac7.bz2
+ <br>
+ (See also <a href="http://www.citi.umich.edu/projects/citi-netscape/reports/poll.html">this patch
+ to make poll scale beyond 1024 fd's</a>.  It's dated Dec 1998; I think it's already in the 2.2.5 kernel.)
+ <li>Any Unix: the limits set by ulimit or setrlimit.
+ </ul>
+ 
+ <h2>Limits on threads</h2>
+ <ul>
+ <li>Solaris: it supports as many threads as will fit in memory, I hear.
+ <li>FreeBSD: ?
+ <li>Linux: Even the 2.2.2 kernel limits the number of threads,
+ at least on Intel.  I don't know what the limits are on other architectures.
+ <a href="http://www.dejanews.com/getdoc.xp?AN=420466972">Mingo posted a patch
+ for 2.1.131 on Intel</a> that removed this limit; I hear he intends to
+ provide updated patches as time goes on, until it's time to integrate it
+ into the main version of the kernel.
+ <li>Java: See <a
+ href="http://www.javaworld.com/javaworld/jw-03-1999/jw-03-volanomark.html">the
+ Volanomark benchmark writeup in Javaworld</a>.  It recommends reducing
+ the amount of memory reserved by default for each thread.
+ </ul>
+ 
+ <h2>Other limits/tips</h2>
+ <ul>
+ <li>select() is limited to FD_SETSIZE handles.  This limit is compiled in to
+ the standard library and user programs.  The similar call poll() does not have
+ a comparable limit, and can have less overhead than select().
+ <li>Even the most recent glibc might use 16 bit variables to hold thread 
+ or file handles, which could cause trouble above 32767 handles/threads.
+ <li>Too much thread-local memory is preallocated by some operating systems;
+ if each thread gets 1MB, and total VM space is 2GB, that creates an upper limit
+ of 2000 threads.
+ <li>Normally, data gets copied many times on its way from here to there.
+ mmap() and sendfile() can be used to reduce this overhead in some cases.
+ <a href="http://www.dejanews.com/getdoc.xp?AN=450465542">IO-Lite</a> 
+ is a proposal (already implemented on FreeBSD) for a set of
+ I/O primitives that gets rid of the need for many copies.
+ It's sexy; go read it.  But see also <a href="http://www.linuxhq.com/lnxlists/linux-kernel/lk_9905_01/msg00263.html">Alan Cox's opinion of zero-copy</a>.
+ <li>The sendfile() function in Linux and FreeBSD lets you tell the kernel to send part 
+ or all of a file.  This lets the OS do it as efficiently as possible.
+ It can be used equally well in servers using threads or servers using
+ nonblocking I/O.  (In Linux, It's poorly documented at the moment; <a
+ href="http://www.dejanews.com/getdoc.xp?AN=422899634">use _syscall4 to 
+ call it</a>.  Andi Kleen is writing new man pages that cover this.)  
+ <a href="http://www.dejanews.com/getdoc.xp?AN=423005088">Rumor has it</a>, 
+ ftp.cdrom.com benefitted noticably from sendfile().
+ <li>A new socket option under Linux, TCP_CORK, tells the kernel to
+ avoid sending partial frames, which helps a bit e.g. when there are
+ lots of little write() calls you can't bundle together for some reason.
+ Unsetting the option flushes the buffer.
+ <li>Not all threads are created equal.  The clone() function in Linux
+ (and its friends in other operating systems)
+ lets you create a thread that has its own current working directory,
+ for instance, which can be very helpful when implementing an ftp server.
+ See Hoser FTPd for an example of the use of native threads rather than pthreads.
+ <li>To keep the number of filehandles per process down, servers
+ can fork() once they reach the desired maximum; the child 
+ finishes serving the existing clients, and the parent accepts and
+ services new clients.  (If the desired maximum is 1, this degenerates
+ to the classical one-process-per-client model.)
+ <li>One developer using sendfile() with Freebsd reports that using
+ POLLWRBAND instead of POLLOUT makes a big difference.  
+ <li>Look at the performance comparison graph at the bottom of
+ <a href="http://www.acme.com/software/thttpd/benchmarks.html">http://www.acme.com/software/thttpd/benchmarks.html</a>.
+ Notice how various servers have trouble above 128 connections, even on Solaris 2.6?  
+ Anyone who figures out why, let me know.  
+ <br>
+ Note: if the TCP stack has a bug that causes a short (200ms)
+ delay at SYN or FIN time, as Linux 2.2.0-2.2.6 had, and the OS or
+ http daemon has a hard limit on the number of connections open,
+ you would expect exactly this behavior.  There may be other causes.
+ <li>"Re: fix for hybrid server problems" by Vivek Sadananda Pai 
+ (vivek@cs.rice.edu) on 
+ <a href="http://www.humanfactor.com/cgi-bin/cgi-delegate/apache-ML/nh/1999/">new-httpd</a>, May 9th, notes:
+ <blockquote> 
+ "I've compared the raw performance of a select-based server with a
+ multiple-process server on both FreeBSD and Solaris/x86. On
+ microbenchmarks, there's only a marginal difference in performance
+ stemming from the software architecture. The big performance win for
+ select-based servers stems from doing application-level caching. While
+ multiple-process servers can do it at a higher cost, it's harder to
+ get the same benefits on real workloads (vs microbenchmarks).
+ I'll be presenting those measurements as part of a paper that'll
+ appear at the next Usenix conference. If you've got postscript,
+ the paper is available at 
+ <a href="http://www.cs.rice.edu/~vivek/flash99/">http://www.cs.rice.edu/~vivek/flash99/</a>"
+ </blockquote>
+ </ul>
+ 
+ <h2>Kernel Issues</h2> 
+ For Linux, it looks like kernel bottlenecks are being fixed constantly.
+ See <a href="http://www.linuxhq.com/">Linux HQ</a>, 
+ <a href="http://www.kt.opensrc.org/">Kernel Traffic</a>,
+ and <a href="http://www.linuxhq.com/lnxlists/linux-kernel/">the Linux-Kernel mailing list</a>
+ (Example interesting posts by 
+ <a href="http://www.linuxhq.com/lnxlists/linux-kernel/lk_9904_03/msg00146.html">a user asking how to tune</a>, and
+ <a href="http://www.linuxhq.com/lnxlists/linux-kernel/lk_9904_03/msg00309.html">Dean Gaudet</a>)
+ <p>
+ In March 1999, Microsoft sponsored a benchmark comparing NT to Linux
+ at serving large numbers of http and smb clients, in which they
+ failed to see good results from Linux.  
+ See also <a href="mindcraft_redux.html">my article on Mindcraft's April 1999 Benchmarks</a>
+ for more info.
+ <p>
+ See also <a href="http://www.citi.umich.edu/projects/citi-netscape/">The Linux Scalability Project</a>.
+ 
+ <h2>Measuring Server Performance</h2>
+ Two tests in particular are simple, interesting, and hard: 
+ <ol>
+ <li>raw connections per second (how many 512 byte files per second can you
+ serve?)
+ <li>total transfer rate on large files with many slow clients
+ (how many 28.8k modem clients can simultaneously download
+ from your server before performance goes to pot?)
+ </ol>
+ Jef Poskanzer has published benchmarks comparing many web servers.
+ See <a href="http://www.acme.com/software/thttpd/benchmarks.html">http://www.acme.com/software/thttpd/benchmarks.html</a>  
+ for his results.
+ <p>
+ I also have 
+ <a href="http://www.alumni.caltech.edu/~dank/fixing-overloaded-web-server.html">
+ a few old notes about comparing thttpd to Apache</a> that may be of interest
+ to beginners.
+ 
+ <h2>Interesting select()-based servers</h2>
+ <ul>
+ <li><a href="http://www.acme.com/software/thttpd/">thttpd</a>
+ Very simple.  Uses a single process.  It has good performance,
+ but doesn't scale with the number of CPU's.
+ <li><a href="http://mathop.diva.nl/">mathopd</a>.  Similar to thttpd.
+ <li><a href="http://www.zeustech.net/">Zeus</a>, a commercial server that tries to be the absolute fastest.
+ See their <a href="http://support.zeustech.net/tuning.htm">tuning guide</a>.   
+ <li>The other non-Java servers listed at <a href="http://www.acme.com/software/thttpd/benchmarks.html">http://www.acme.com/software/thttpd/benchmarks.html</a>
+ <li><a
+ href="http://ca.us.mirrors.freshmeat.net/appindex/1999/02/17/919251275.html">BetaFTPd</a>
+ <li><a href="http://www.cs.rice.edu/~vivek/iol98/">Flash-Lite</a> -
+ web server using IO-Lite.
+ <li><a
+ href="http://www.imatix.com/html/xitami/">xitami</a> - uses select() to
+ implement its own thread abstraction for portability to systems without 
+ threads.
+ <li><a href="http://www.nightmare.com/medusa/medusa.html">Medusa</a> - a server-writing toolkit in Python that tries to deliver very high performance. 
+ </ul>
+ 
+ <h2>Interesting thread-based servers</h2>
+ <ul>
+ <li><a href="http://www.zabbo.net/hftpd/">Hoser FTPD</a>.
+ See their <a href="http://www.zabbo.net/hftpd/bench.html">benchmark page</a>.
+ <li><a
+ href="http://ca.us.mirrors.freshmeat.net/appindex/1999/02/06/918317238.html">Peter Eriksson's phttpd</a> and <li><a href="http://ca.us.mirrors.freshmeat.net/appindex/1999/02/06/918313631.html">pftpd</a> 
+ <li>The Java-based servers listed at <a href="http://www.acme.com/software/thttpd/benchmarks.html">http://www.acme.com/software/thttpd/benchmarks.html</a>
+ <li>Sun's <a href="http://jserv.javasoft.com/">Java Web Server</a>
+ (which has been 
+ <a
+ href="http://archives.java.sun.com/cgi-bin/wa?A2=ind9901&L=jserv-interest&F=&S=&P=47739">reported to handle 500 simultaneous clients</a>)
+ </ul>
+ 
+ <h2>Other interesting servers</h2>
+ <ul>
+ <li><a href="http://www.novell.com/bordermanager/ispcon4.html">Novell's
+ FastCache</a> -- claims 10000 hits per second.  Quite the pretty performance graph.
+ </ul>
+ 
+ <hr>
+ <i>Copyright 1999 Dan Kegel</i><br>
+ dank@alumni.caltech.edu<br>
+ Last updated: 9 May 1999<br>
+ <a href="http://www.kegel.com">[Return to www.kegel.com]</a>
+ </body>
+ </html>
+ 


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+ From dgaudet-list-new-httpd@arctic.org Mon Mar 13 11:11:15 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-660-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: Buff should be an I/O layer
+ Date: 12 Mar 2000 19:24:28 +0100
+ Organization: Mail2News at engelschall.com
+ Lines: 41
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003120948410.6274-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 952885468 17709 141.1.129.1 (12 Mar 2000 18:24:28 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 12 Mar 2000 18:24:28 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:36319
+ 
+ On Fri, 10 Mar 2000, Manoj Kasichainula wrote:
+ 
+ > Random thought that I thought should go to the list before I forget
+ > it:
+ > 
+ > BUFF's API should be redone to look exactly like an IOL. As far as the
+ > rest of Apache code is concerned, a IOL with a buff around it
+ > should look just like any other IOL.
+ 
+ haha!
+ 
+ if you figure this out, then rad.  i tried for a long time to figure out a
+ clean way to do this which doesn't suck and i never found one.
+ 
+ remember it is totally unacceptable for bputc() and bgetc() to be anything
+ other than macros operating directly on the buffer.
+ 
+ > First of all, we get more uniformity in the API. That's always a good
+ > thing. This also allows us to yank out the buff IOL sometimes. I can
+ > see this being useful if a really sophisticated module wants to truly
+ > eliminate the buffering between it and the client.
+ 
+ the BUFF layer allows you to run without buffering, or with non-blocking
+ i/o, and it implements chunking.  you gain a mere few cycles by "yanking
+ it out".
+ 
+ you might say "chunking should be a layer too", see my above laughter.
+ 
+ the only way you're going to make a change like this "clean" is to add a
+ sophisticated zero-copy implementation.  i stopped short of doing this
+ because in my experience using one of these, the benefits are really
+ minimal.  <http://www.canonware.com/sqrl/> look in libstash.
+ 
+ the only case where i've seen the zero-copy stuff really shine is when
+ doing TCP-to-TCP proxying.  for everything else, the (comparatively
+ simple) heuristics present in BUFF are all that's required.
+ 
+ Dean
+ 
+ 
+ 
+ From dgaudet-list-new-httpd@arctic.org Mon Mar 13 11:11:44 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-661-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: Buff should be an I/O layer
+ Date: 12 Mar 2000 19:24:30 +0100
+ Organization: Mail2News at engelschall.com
+ Lines: 41
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003121001550.6274-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 952885470 17739 141.1.129.1 (12 Mar 2000 18:24:30 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 12 Mar 2000 18:24:30 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:36320
+ 
+ 
+ 
+ On Sun, 12 Mar 2000, Dean Gaudet wrote:
+ 
+ > the only way you're going to make a change like this "clean" is to add a
+ 
+ i should clarify this... the only *portable* way is blah blah blah.
+ 
+ if all unixes supported TCP_CORK, and had very inexpensive syscall
+ overhead like linux does then we wouldn't have to do much work at all --
+ we could take advantage of the fact that the kernel generally has to do a
+ single copy of all the bytes anyhow.
+ 
+ TCP_CORK, for those not aware of it, is a very much needed correction to
+ the TCP API.  specifically, the traditional API gives us the two options:
+ 
+ - nagle on: the kernel makes somewhat arbitrary decisions as to where to
+ form your TCP packet boundaries, you might get lucky and two small writes
+ will be combined into one packet... or you might get unlucky and your
+ packets will be delayed causing performance degredation.
+ 
+ - nagle off: each write() can, and usually does, cause a packet boundary.
+ 
+ it's pretty much the case that no matter which option you choose it
+ results in performance degredation.
+ 
+ with TCP_CORK the kernel is permitted to send any complete frames, but
+ can't send any final partial frames until the cork is removed.  this lets
+ user applications use write(), which is *far* more natural to use than
+ writev() ...
+ 
+ writev() is essentially an optimisation for kernels with expensive syscall
+ overhead :)
+ 
+ i think TCP_CORK is still unique to linux.  they added it when they were
+ implementing sendfile() and i pointed out the packet boundary problems and
+ asked for this new api... most other sendfile() implementations are
+ kludges bundling up sendfile and writev for the headers and trailers.
+ 
+ Dean
+ 
+ From dgaudet-list-new-httpd@arctic.org Tue Apr 11 08:16:13 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-2246-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (dean gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: SAFEREAD (was Re: Buff should be an I/O layer)
+ Date: 11 Apr 2000 07:12:07 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 31
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0004101511380.7822-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 955429927 94666 141.1.129.1 (11 Apr 2000 05:12:07 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 11 Apr 2000 05:12:07 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37614
+ 
+ On Mon, 10 Apr 2000, dean gaudet wrote:
+ 
+ > if you do that against apache-1.3 and the current apache-2.0 you get
+ > back maximally packed packets.
+ 
+ heh, no 2.0 is broken.  i broke SAFEREAD during the initial mpm work --
+ and it hasn't been re-implemented yet.
+ 
+ does someone else want to fix this?  it's probably not ideal that i'm the
+ only person intimately familiar with this code :)
+ 
+ without SAFEREAD, we end up with a packet boundary between every response
+ in a pipelined connection.
+ 
+ essentially saferead ensures that if we are going to have to block in
+ read() to get the next request on a connection then we better flush our
+ output buffer (otherwise we cause a deadlock with non-pipelining clients).  
+ but if there are more bytes available, then we don't need to flush our
+ output buffer.
+ 
+ if you search the code for SAFEREAD you'll see i suggest that it might be
+ implemented as a layer.  i'm not sure what i meant, i don't think this
+ works.
+ 
+ if you look at 1.3's saferead and bhalfduplex in buff.c you'll see that we
+ use select() to implement it.  naturally this won't work in 2.0... but
+ what will work is to set the iol's timeout to 0 and attempt a read.  
+ underneath the covers this achieves the same result.
+ 
+ -dean
+ 
+ From dgaudet-list-new-httpd@arctic.org Thu Apr 13 14:10:41 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-2263-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (dean gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: question about the STATUS entry for lingering close
+ Date: 11 Apr 2000 18:35:53 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 74
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0004110902390.10177-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 955470953 15153 141.1.129.1 (11 Apr 2000 16:35:53 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 11 Apr 2000 16:35:53 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37624
+ 
+ On Tue, 11 Apr 2000, Jeff Trawick wrote:
+ 
+ > >   * Fix lingering close
+ > >       Status:
+ > 
+ > Does 2.0 regress one or more of the solutions in 1.3, or was some
+ > improvement (other than async I/O) envisioned?
+ 
+ this actually isn't about implementing SO_LINGER stuff... that should be
+ avoided at all costs -- SO_LINGER works on very few kernels.  actually
+ i'm tempted to say rip out all the SO_LINGER stuff.
+ 
+ we need lingering_close() re-implemented, it's in main/http_connection.c.
+ 
+ to do that we need to add a shutdown() method to ap_iol_methods, and i
+ suggest an ap_bshutdown() added to BUFF.
+ 
+ and then lingering_close() needs to be re-implemented something like
+ the code below.
+ 
+ -dean
+ 
+ /* we now proceed to read from the client until we get EOF, or until
+  * MAX_SECS_TO_LINGER has passed.  the reasons for doing this are
+  * documented in a draft:
+  *
+  * http://www.ics.uci.edu/pub/ietf/http/draft-ietf-http-connection-00.txt
+  *
+  * in a nutshell -- if we don't make this effort we risk causing
+  * TCP RST packets to be sent which can tear down a connection before
+  * all the response data has been sent to the client.
+  */
+ 
+ static void lingering_close(request_rec *r)
+ {
+     char dummybuf[IOBUFFERSIZE];
+     ap_time_t start;
+     ap_ssize_t nbytes;
+     ap_status_t rc;
+     int timeout;
+ 
+     /* Send any leftover data to the client, but never try to again */
+ 
+     if (ap_bflush(r->connection->client) != APR_SUCCESS) {
+        ap_bclose(r->connection->client);
+        return;
+     }
+     /* XXX: hrm, setting B_EOUT should probably be part of ap_bshutdown() */
+     ap_bsetflag(r->connection->client, B_EOUT, 1);
+ 
+     if (ap_bshutdown(r->connection->client, 1) != APR_SUCCESS
+        || ap_is_aborted(r->connection)) {
+        ap_bclose(r->connection->client);
+        return;
+     }
+ 
+     start = ap_now();
+     timeout = MAX_SECS_TO_LINGER;
+     for (;;) {
+        ap_bsetopt(r->connection->client, BO_TIMEOUT, &timeout);
+        rc = ap_bread(r->connection->client, dummybuf, sizeof(dummybuf), &nbytes);
+        if (rc != APR_SUCCESS) break;
+ 
+        /* how much time has elapsed? */
+        timeout = (ap_now() - start) / AP_USEC_PER_SEC;
+        if (timeout >= MAX_SECS_TO_LINGER) break;
+ 
+        /* figure out the new timeout */
+        timeout = MAX_SECS_TO_LINGER - timeout;
+     } 
+ 
+     ap_bclose(r->connection->client);
+ }
+ 
+ From dgaudet-list-new-httpd@arctic.org Tue Mar 28 11:34:53 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1510-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: canonical list of i/o layering use cases
+ Date: 28 Mar 2000 07:04:07 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 93
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003271648270.14812-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954219847 46303 141.1.129.1 (28 Mar 2000 05:04:07 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Mar 2000 05:04:07 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37027
+ 
+ i really hope this helps this discussion move forward.
+ 
+ the following is the list of all applications i know of which have been
+ proposed to benefit from i/o layering.
+ 
+ - data sink abstractions:
+        - memory destination (for ipc; for caching; or even for abstracting
+                things such as strings, which can be treated as an i/o
+                object)
+        - pipe/socket destination
+        - portability variations on the above
+ 
+ - data source abstraction, such as:
+        - file source (includes proxy caching)
+        - memory source (includes most dynamic content generation)
+        - network source (TCP-to-TCP proxying)
+        - database source (which is probably, under the covers, something like
+                a memory source mapped from the db process on the same box,
+                or from a network source on another box)
+        - portability variations in the above sources
+ 
+ - filters:
+        - encryption
+        - translation (ebcdic, unicode)
+        - compression
+        - chunking
+        - MUX
+        - mod_include et al
+ 
+ and here are some of my thoughts on trying to further quantify filters:
+ 
+ a filter separates two layers and is both a sink and a source.  a
+ filter takes an input stream of bytes OOOO... and generates an
+ output stream of bytes which can be broken into blocks such
+ as:
+ 
+        OOO NNN O NNNNN ...
+ 
+        where O = an old or original byte copied from the input
+        and N = a new byte generated by the filter
+ 
+ for each filter we can calculate a quantity i'll call the copied-content
+ ratio, or CCR:
+ 
+        nbytes_old / nbytes_new
+ 
+ where:
+        nbytes_old = number of bytes in the output of the
+                filter which are copied from the input
+                (in zero-copy this would mean "copy by
+                reference counting an input buffer")
+        nbytes_new = number of bytes which are generated
+                by the filter which weren't present in the
+                input
+ 
+ examples:
+ 
+ CCR = infinity:  who cares -- straight through with no
+        transformation.  the filter shouldn't even be there.
+ 
+ CCR = 0: encryption, translation (ebcdic, unicode), compression.
+        these get zero benefit from zero-copy.
+ 
+ CCR > 0: chunking, MUX, mod_include
+ 
+ from the point of view of evaluating the benefit of zero-copy we only
+ care about filters with CCR > 0 -- because CCR = 0 cases degenerate into
+ a single-copy scheme anyhow.
+ 
+ it is worth noting that the large_write heuristic in BUFF fairly
+ clearly handles zero-copy at very little overhead for CCRs larger than
+ DEFAULT_BUFSIZE.
+ 
+ what needs further quantification is what the CCR of mod_include would
+ be.
+ 
+ for a particular zero-copy implementation we can find some threshold k
+ where filters with CCRs >= k are faster with the zero-copy implementation
+ and CCRs < k are slower... faster/slower as compared to a baseline
+ implementation such as the existing BUFF.
+ 
+ it's my opinion that when you consider the data sources listed above, and
+ the filters listed above that *in general* the existing BUFF heuristics
+ are faster than a complete zero-copy implementation.
+ 
+ you might ask how does this jive with published research such as the
+ IO-Lite stuff?  well, when it comes right down to it, the research in
+ the IO-Lite papers deal with very large CCRs and contrast them against
+ a naive buffering implementation such as stdio -- they don't consider
+ what a few heuristics such as apache's BUFF can do.
+ 
+ Dean
+ 
+ From dgaudet-list-new-httpd@arctic.org Tue Mar 28 11:35:26 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1524-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: canonical list of i/o layering use cases
+ Date: 28 Mar 2000 07:04:14 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 15
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003271834330.7309-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954219854 46403 141.1.129.1 (28 Mar 2000 05:04:14 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Mar 2000 05:04:14 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37035
+ 
+ On Mon, 27 Mar 2000, Dean Gaudet wrote:
+ 
+ > CCR = infinity:  who cares -- straight through with no
+ >      transformation.  the filter shouldn't even be there.
+ 
+ thanks to ronald for pointing out CCR = infinity filters -- hash
+ calculations.
+ 
+ thankfully they're trivial to handle without a full zero-copy
+ implementation, so i still stand by my assertions.
+ 
+ please to submit more filters/sources/sinks i haven't considered yet.
+ 
+ Dean
+ 
+ From dgaudet-list-new-httpd@arctic.org Tue Mar 28 11:38:30 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1494-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: layered I/O (was: cvs commit: ...)
+ Date: 28 Mar 2000 07:02:15 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 47
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003271523050.26572-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954219735 45661 141.1.129.1 (28 Mar 2000 05:02:15 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Mar 2000 05:02:15 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37016
+ 
+ On Mon, 27 Mar 2000, Roy T. Fielding wrote:
+ 
+ > Whatever we do, it needs to be clean enough to enable later performance
+ > enhancements along the lines of zero-copy streams.
+ 
+ good luck, i think it's impossible.  any code written to a read/write
+ interface is passing around buffers with no reference counts, and the
+ recipients of those buffers (the i/o layers) must immediately copy the
+ contents before returning to the caller.  zero-copy requires reference
+ counted buffers.  therefore any future zero-copy enhancement would require
+ substantial code changes to the callers -- the modules.
+ 
+ btw -- the code, as is, already supports zero-copy for those cases where
+ it's actually a win... the cases where bwrite() is called with a large
+ enough buffer, and we're able to pass it to the kernel immediately.
+ 
+ i honestly believe there are very few applications which benefit from
+ zero-copy.  encryption and compression obvious don't, they require a copy.  
+ what other layers would there be in the stack?
+ 
+ a mod_include-type filter which was doing zero-copy would probably be
+ slower than it is now... that'd be using zero-copy to pass little bits and
+ pieces of strings, the bits and pieces which were unchanged by the filter.  
+ zero-copy has all this overhead in maintaining the lists of buffers and
+ the reference counts... more overhead in that than in the rather simple
+ heuristics present in BUFF.
+ 
+ a MUX layer might benefit from zero-copy ... but after doing lots of
+ thinking on this a year ago i remain completely unconvinced that zero-copy
+ from end to end is any better than the heuristics we already have... and
+ the answer is different depending on how parallel mux requests are
+ serviced (whether by threads or by an async core).
+ 
+ there is one application i know of that benefits from zero-copy -- and
+ that is TCP to TCP tunnelling.  but even here, the biggest win i've seen
+ is not from the zero-copy per se, as much as it is from wins you can get
+ in reducing the need to have a bunch of 4k userland buffers for each
+ socket.
+ 
+ zero-copy is a very nice theoretical toy.  i'm still waiting for a good
+ demonstration or use case.
+ 
+ i hope you don't hold up improvements in apache while this research is
+ going on.
+ 
+ Dean
+ 
+ From dgaudet-list-new-httpd@arctic.org Tue Mar 28 11:40:37 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1514-rse+apache=en.muc.de
+ From: dgaudet-list-new-httpd@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: layered I/O (was: cvs commit: ...)
+ Date: 28 Mar 2000 07:04:08 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 22
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003271759460.5154-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954219848 46333 141.1.129.1 (28 Mar 2000 05:04:08 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Mar 2000 05:04:08 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37028
+ 
+ On Sun, 26 Mar 2000, Greg Stein wrote:
+ 
+ > Below, you talk about doing this without performance implications. Well,
+ > that loop is one that you've added. :-)
+ 
+ it's very easy to optimize the loop further -- by hashing the strings
+ which run the direct matches.
+ 
+ it's really helpful to consider a simple example:
+ 
+ accessing foo.cgi, which generates "Content-Type: text/x-parsed-html"
+ which requires mod_include to run.
+ 
+ to run foo.cgi r->handler is set to "cgi-handler", which assuming we do
+ the hash right, is picked off immediately and run without looping.
+ 
+ then r->content_type is updated, and set to "text/x-parsed-html", and
+ again, if we've done the hash right, then it's picked off immediately
+ without looping.
+ 
+ Dean
+ 
+ From bhyde@pobox.com Wed Mar 29 08:28:32 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1539-rse+apache=en.muc.de
+ From: bhyde@pobox.com (Ben Hyde)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: canonical list of i/o layering use cases
+ Date: 28 Mar 2000 19:26:56 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 44
+ Approved: postmaster@m2ndom
+ Message-ID: <87ln335fbt.fsf@pobox.com>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954264417 68771 141.1.129.1 (28 Mar 2000 17:26:57 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Mar 2000 17:26:57 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37045
+ 
+ Dean Gaudet <dgaudet-list-new-httpd@arctic.org> writes:
+ > please to submit more filters/sources/sinks i haven't considered yet.
+ 
+ :-)
+ 
+ This discussion flairs up from time to time, doesn't it!
+ 
+ The last time this flared up I came to the opinion that
+ there is a knot here worth illuminating, but I can't recall
+ if I bothered to say it outloud here.
+ 
+ The inside of the knot is: planning, authorizing, executing.
+ 
+ The request arrives and the beast has to assemble a plan for
+ how to respond.  These plans can, and ought to be, reasonably
+ ornate; at least a tree.  The primitive nodes are things like
+ stream this file, do this character set conversion, etc.  The
+ slightly more complex nodes do things like store results in
+ caches, and assemble bits into bundles, etc.  The core ought
+ to provide a way to manipulate these plans.  The types of nodes
+ and the operation sets on them should be provided by modules.
+ 
+ Given the plan then the problem is to decide if this is approprate
+ to execute it.  I.e. do we have all the rights we need.  This is
+ a mess because it needs to draw information from three domains,
+ the client's credentials, the process/thread rights, and the 
+ protection configuration on the named objects that are inputs to
+ the plan.
+ 
+ Finally execution.  The execution is where we start wanting
+ terrific efficencies.  Zero copy, clever caching, kernel hackery,
+ levering O/S specific delights like sendfile.
+ 
+ The outside of the knot of plan/auth/exec is the necessity of
+ letting all three phases spread across machines, processes, threads,
+ code cult, and projects.  (This is why that www.spread.org work is 
+ so right on).
+ 
+ I suspect it was at about this point in my thinking that I become
+ happy that this was slipping outside the scope of 2.0 where it
+ could stew longer.
+ 
+  - ben
+ 
+ From fielding@kiwi.ICS.UCI.EDU Wed Mar 29 14:05:46 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1593-rse+apache=en.muc.de
+ From: fielding@kiwi.ICS.UCI.EDU ("Roy T. Fielding")
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: layered I/O (was: cvs commit: ...)
+ Date: 29 Mar 2000 07:58:05 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 65
+ Approved: postmaster@m2ndom
+ Message-ID: <200003282119.aa05413@gremlin-relay.ics.uci.edu>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954309485 4205 141.1.129.1 (29 Mar 2000 05:58:05 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 29 Mar 2000 05:58:05 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37088
+ 
+ >> Bite me. You're being totally confrontational here, and it isn't called
+ >> for. You didn't read my statements. I said no change to generators, and
+ >> definite changes to processors.
+ >
+ >no it is called for.
+ >
+ >this item has been on the bullet list for as long as apache-2.0 has been a
+ >wet dream.
+ >
+ >there's been a fuckload of hand waving over the years, and *no code*.  
+ >code speaks reams more in my book than anything else.
+ >
+ >so far all i'm seeing is more hand waving, and cries that this isn't the
+ >wet dream folks thought it would be.
+ >
+ >welcome to reality.  if you folks would stop waving your hands and
+ >actually try to code it up you'd probably understand our proposed
+ >solution.
+ 
+ Dean, this is crossing my tolerance threshold for bullshit.  You haven't
+ even looked at the code that was committed.  If you had, you would notice
+ that it doesn't implement IO-layering.  What it implements is IO-relaying
+ and an infinite handler loop.  This isn't handwaving.  The code simply
+ doesn't do IO-layering.  Period.
+ 
+ Layered-IO involves a cascaded sequence of filters that independently
+ operate on a continuous stream in an incremental fashion.  Relayed-IO
+ is a sequence of processing entities that opportunistically operate
+ on a unit of data to transform it to some other unit of data, which
+ can then be made available again to the other processing entities.
+ The former is called a pipe-and-filter architecture, and the latter
+ is called a blackboard architecture, and the major distinctions between
+ the two are:
+ 
+    1) in layered-IO, the handlers are identified by construction
+       of a data flow network, whereas in relayed-IO the handlers
+       simply exist in a "bag of handlers" and each one is triggered
+       based on the current data state;
+ 
+    2) in layered-IO, the expectation is that the data is processed
+       as a continuous stream moving through handlers, whereas in
+       relayed-IO the data is operated upon in complete units and
+       control is implicitly passed from one processor to the next;
+ 
+    3) in layered-IO, data processing ends at the outer layer,
+       whereas in relayed-IO it ends when the data reaches a special
+       state of "no processing left to be done".
+ 
+ Yes, these two architectures are similar and can accomplish the
+ same tasks, but they don't have the same performance characteristics
+ and they don't have the same configuration interface.  And, perhaps
+ most significantly, relayed-IO systems are not as reliable because
+ it is very hard to anticipate how processing will occur and very easy
+ for the system to become stuck in an infinite loop.
+ 
+ I don't want a blackboard architecture in Apache, regardless of the
+ version of the release or how many users might be satisfied by the
+ features it can implement.  It is unreliable and hard to maintain
+ and adds too much latency to the response processing.  But if somebody
+ else really wants such an architecture, and they understand its implications,
+ then I won't prevent them from going with that solution -- I just
+ don't want them thinking it is what we meant by layered-IO.
+ 
+ ....Roy
+ 
+ From fielding@kiwi.ICS.UCI.EDU Wed Mar 29 14:06:34 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1594-rse+apache=en.muc.de
+ From: fielding@kiwi.ICS.UCI.EDU ("Roy T. Fielding")
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: layered I/O (was: cvs commit: ...)
+ Date: 29 Mar 2000 07:58:15 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 56
+ Approved: postmaster@m2ndom
+ Message-ID: <200003282148.aa06947@gremlin-relay.ics.uci.edu>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954309496 4516 141.1.129.1 (29 Mar 2000 05:58:16 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 29 Mar 2000 05:58:16 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37089
+ 
+ >On Mon, 27 Mar 2000, Roy T. Fielding wrote:
+ >
+ >> Whatever we do, it needs to be clean enough to enable later performance
+ >> enhancements along the lines of zero-copy streams.
+ >
+ >good luck, i think it's impossible.  any code written to a read/write
+ >interface is passing around buffers with no reference counts, and the
+ >recipients of those buffers (the i/o layers) must immediately copy the
+ >contents before returning to the caller.  zero-copy requires reference
+ >counted buffers.  therefore any future zero-copy enhancement would require
+ >substantial code changes to the callers -- the modules.
+ 
+ Yes, assuming we did zero copies.  We could still do the interim thing
+ with one-copy.  I agree that taking advantage of the higher performance
+ would require that the callers be attuned to the high-performance interface.
+ 
+ >btw -- the code, as is, already supports zero-copy for those cases where
+ >it's actually a win... the cases where bwrite() is called with a large
+ >enough buffer, and we're able to pass it to the kernel immediately.
+ >
+ >i honestly believe there are very few applications which benefit from
+ >zero-copy.  encryption and compression obvious don't, they require a copy.  
+ >what other layers would there be in the stack?
+ >
+ >a mod_include-type filter which was doing zero-copy would probably be
+ >slower than it is now... that'd be using zero-copy to pass little bits and
+ >pieces of strings, the bits and pieces which were unchanged by the filter.  
+ >zero-copy has all this overhead in maintaining the lists of buffers and
+ >the reference counts... more overhead in that than in the rather simple
+ >heuristics present in BUFF.
+ 
+ On the contrary, the vast majority of include-based templates
+ consist of large junks of HTML with embedded separators.  With zero-copy
+ you can just split the data into three buckets by reference and
+ replace the middle bucket with the included content, which may
+ itself be a data stream.  Not only does this reduce memory consumption,
+ it also removes almost all of the special-case handling of data sources
+ via subrequests/caching/proxy/whatever and vastly simplifies the
+ SSI/PHP/whatever processing architecture.
+ 
+ >a MUX layer might benefit from zero-copy ... but after doing lots of
+ >thinking on this a year ago i remain completely unconvinced that zero-copy
+ >from end to end is any better than the heuristics we already have... and
+ >the answer is different depending on how parallel mux requests are
+ >serviced (whether by threads or by an async core).
+ 
+ The place where I need zero copy is in the request processing, where
+ the first read off the network may result in multiple requests being
+ placed within the same buffer.  I don't want the initial request to
+ be copied into separate buffers, since I still consider that initial
+ copy to be more overhead than all of the reference counting combined.
+ Maybe I'm just being too pessimistic about the cost of a data copy,
+ and I should optimize around one-copy instead.
+ 
+ ....Roy
+ 
+ From jwbaker@acm.org Wed Mar 29 14:07:15 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1598-rse+apache=en.muc.de
+ From: jwbaker@acm.org ("Jeffrey W. Baker")
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: layered I/O (was: cvs commit: ...)
+ Date: 29 Mar 2000 13:45:26 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 163
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.0003290004100.10357-100000@piglet>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954330326 23160 141.1.129.1 (29 Mar 2000 11:45:26 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 29 Mar 2000 11:45:26 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37093
+ 
+ On Tue, 28 Mar 2000, Roy T. Fielding wrote:
+ [ed]
+ > Layered-IO involves a cascaded sequence of filters that independently
+ > operate on a continuous stream in an incremental fashion.  Relayed-IO
+ > is a sequence of processing entities that opportunistically operate
+ > on a unit of data to transform it to some other unit of data, which
+ > can then be made available again to the other processing entities.
+ > The former is called a pipe-and-filter architecture, and the latter
+ > is called a blackboard architecture, and the major distinctions between
+ > the two are:
+ > 
+ >    1) in layered-IO, the handlers are identified by construction
+ >       of a data flow network, whereas in relayed-IO the handlers
+ >       simply exist in a "bag of handlers" and each one is triggered
+ >       based on the current data state;
+ > 
+ >    2) in layered-IO, the expectation is that the data is processed
+ >       as a continuous stream moving through handlers, whereas in
+ >       relayed-IO the data is operated upon in complete units and
+ >       control is implicitly passed from one processor to the next;
+ > 
+ >    3) in layered-IO, data processing ends at the outer layer,
+ >       whereas in relayed-IO it ends when the data reaches a special
+ >       state of "no processing left to be done".
+ 
+ Forgive me for jumping in here.  Sometimes those of us who are merely
+ observers of the core group do not get a perspective on the design
+ discussions that take place in private emails and in person.  Thus, what I
+ have to say will largely rehash what has been said already.
+ 
+ It seems to me that a well-rounded IO-layering system has already been
+ proposed here, in bits and pieces, by different people, over the course of
+ many threads.  The components of the system are: 1. a routine to place the
+ IO layers in the proper order, 2. a routine to send data between IO
+ layers, and 3. the layers themselves.
+ 
+ Selection of IO Layers
+ 
+ The core selects a source module and IO layers based on the urlspace
+ configuration.  Content might be generated by mod_perl, and the result is
+ piped through mod_chunk, mod_ssl, and mod_net, in turn.  When the content
+ generator runs, the core enforces that the module set the content type
+ before the first call to ap_bput.  The content type is set by a function
+ call.  The function (ap_set_content_type(request_rec *, char *)) examines
+ the content type and adds IO layers as neccessary.  For server parsed
+ html, the core might insert mod_include immediately after mod_perl.
+ 
+ (Can anyone produce a use case where the IO chain could change after
+ output begins?)
+ 
+ Interface Between IO Layers
+ 
+ The core is responsible for marshalling data between the IO layers.  Each
+ layer registers a callback function ((* ap_status_t)(request_rec *,
+ buff_vec *)) on which it receives input.  Data is sent to the next layer
+ using ap_bput(request_rec *, buff_vec *).  The buff_vec is simply an
+ ordered array of address and length pairs.  Whenever ap_bput is called,
+ the input callback of the next layer is called.  No message queueing,
+ async handlers, or any of that business is needed.  ap_bput keeps track of
+ where in the output chain things are.  Control flow in this systems tends
+ to yo-yo up and down the IO chain.  Examples later.
+ 
+ The only other part of the IO interface is a flush routine.  The IO layers
+ are free to implement whatever they feel flushing involves.
+ 
+ There are two notable things about this system.  First, control flow need
+ not ever reach the end of the output chain.  Any layer is free to return
+ without calling ap_bput.  The layers can do whatever they please with the
+ data.  The network module would be such an example.  It would always write
+ the buffers over the network, and never pass them down the IO chain.  If
+ mod_ssl wanted to handle networking itself, it could do that, too.  The
+ second notable thing is that once a buffer has been sent down the chain,
+ it is gone forever.  Later layers are responsible for freeing the memory
+ and whatnot.  Diddling in a buffer that has already been sent would be bad
+ form.
+ 
+ Layer Implementation
+ 
+ This system has implications for the design and implementation of the
+ layers.  Clearly, it would not be efficient to call ap_bput overly much.  
+ Also, the IO layers must be re-entrant in the threaded MPMs, so they will
+ need some mechanism for storing module-specific state information in the
+ request context (think mod_include when an include directive spans ap_bput
+ calls).
+ 
+ There will be basically three types of layers: those that insert content
+ into the stream (chunking, SSI), those that replace the stream completely
+ (encryption, compression), and those that sink the stream (network).  The
+ layers all demonstrate minimal copying: the inserting layers merely move
+ the boundaries on the incoming buffers and insert a new buffer.  The
+ replacement layers have to create a new buffer and dealloc the old one,
+ but you can't avoid that in any case.  The sinks merely dealloc the
+ buffers, so no problems there.
+ 
+ Analysis by Example
+ 
+ I considered two examples when coming up with this design.  One is content
+ which is dynamically generated by mod_perl, filtered through SSI, chunked,
+ encrypted, and sent over the wire.  The other is fast static content
+ serving, where a module is blasting out pre-computed HTTP responses a la
+ SGI's 10x patches.
+ 
+ In the first situation, imagine that a 10 KB document is generated which
+ contains two include directives.  The include directives insert a standard
+ banner and the contents of a 40 KB file.  The generating module outputs
+ the data via one ap_set_content_type call and five separate ap_bput calls.  
+ To see the worst case, assume that both include directives span ap_bput
+ calls.  Assume that the included content does not contain any include
+ directives.
+ 
+ The IO chain initially looks like this:
+ 
+ mod_perl->mod_chunk->mod_ssl->mod_net
+ 
+ After the content type is set, the chain changes:
+ 
+ mod_perl->mod_include->mod_chunk->mod_ssl->mod_net
+ 
+ During the inclusion of the 40 KB file, mod_include allocates a series of
+ 4 KB buffers, fills them from the file, and sends them down the chain (or
+ maybe it uses mmap).  The analysis is left to the reader, but the end
+ result is that ap_bput is called 50 times during the request phase.  Is
+ that a lot?  Consider the amount of work being done, and the fact that we
+ have avoided all the overhead of using, for example, actual pipes, or
+ thread-safe queueing.  Calling functions in a single userland context is
+ known to be fast.  The number of calls could be reduced if mod_include
+ used a larger internal buffer, but at the expense of memory consumption
+ (or it could use mmap).  Note also that the number of ap_bput calls does
+ not translate into packets on the wire.  mod_net is free to do whatever is
+ optimal with respect to packet boundaries.
+ 
+ The second example represents high performance static content delivery.  
+ The content-generating module has all headers and content cached or mapped
+ in memory.  The entire output phase is accomplished in a single ap_bput
+ call, and the networking module does The Right Thing to ensure best
+ network usage.
+ 
+ Am I rambling yet?  I'd like to get some opinions on this system, if
+ anybody feels it is significantly different from those already proposed.  
+ I realize that I have waved my hands regarding actually deciding when to
+ use what IO layers and where, but I am confident that a logically
+ appealing system could be devised.
+ 
+ Regards, 
+ Jeffrey
+ 
+ > 
+ > Yes, these two architectures are similar and can accomplish the
+ > same tasks, but they don't have the same performance characteristics
+ > and they don't have the same configuration interface.  And, perhaps
+ > most significantly, relayed-IO systems are not as reliable because
+ > it is very hard to anticipate how processing will occur and very easy
+ > for the system to become stuck in an infinite loop.
+ > 
+ > I don't want a blackboard architecture in Apache, regardless of the
+ > version of the release or how many users might be satisfied by the
+ > features it can implement.  It is unreliable and hard to maintain
+ > and adds too much latency to the response processing.  But if somebody
+ > else really wants such an architecture, and they understand its implications,
+ > then I won't prevent them from going with that solution -- I just
+ > don't want them thinking it is what we meant by layered-IO.
+ 
+ 
+ From fielding@kiwi.ICS.UCI.EDU Wed Mar 29 14:07:48 2000
+ Path: engelschall.com!mail2news!apache.org!new-httpd-return-1599-rse+apache=en.muc.de
+ From: fielding@kiwi.ICS.UCI.EDU ("Roy T. Fielding")
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: layered I/O (was: cvs commit: ...)
+ Date: 29 Mar 2000 13:45:30 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 43
+ Approved: postmaster@m2ndom
+ Message-ID: <200003290205.aa19557@gremlin-relay.ics.uci.edu>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 954330330 23243 141.1.129.1 (29 Mar 2000 11:45:30 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 29 Mar 2000 11:45:30 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:37094
+ 
+ >Selection of IO Layers
+ >
+ >The core selects a source module and IO layers based on the urlspace
+ >configuration.  Content might be generated by mod_perl, and the result is
+ >piped through mod_chunk, mod_ssl, and mod_net, in turn.  When the content
+ >generator runs, the core enforces that the module set the content type
+ >before the first call to ap_bput.  The content type is set by a function
+ >call.  The function (ap_set_content_type(request_rec *, char *)) examines
+ >the content type and adds IO layers as neccessary.  For server parsed
+ >html, the core might insert mod_include immediately after mod_perl.
+ 
+ The problem of thinking of it that way is that, like Dean mentioned,
+ the output of one module may be filtered and the filter indicate that
+ content should be embedded from another URL, which turns out to be a
+ CGI script that outputs further parseable content.  In this instance,
+ the goal of layered-IO is to abstract away such behavior so that the
+ instance is processed recursively and thus doesn't result in some tangled
+ mess of processing code for subrequests.  Doing it requires that each
+ layer be able to pass both data and metadata, and have both data and
+ metadata be processed at each layer (if desired), rather than call a
+ single function that would set the metadata for the entire response.
+ 
+ My "solution" to that is to pass three interlaced streams -- data,
+ metadata, and meta-metadata -- through each layer.  The metadata
+ streams would point to a table of tokenized name-value pairs.
+ There are lots of ways to do that, going back to my description of
+ bucket brigades long ago.  Basically, each block of memory would
+ indicate what type of data, with metadata occurring in a block before
+ the data block(s) that it describes (just like chunk-size describes
+ the subsequent chunk-data) and the layers could be dynamically
+ rearranged based on the metadata that passed through them, in
+ accordance with the purpose of the filter.
+ 
+ >(Can anyone produce a use case where the IO chain could change after
+ >output begins?)
+ 
+ Output is a little easier, but that is the normal case for input.
+ We don't know what filters to apply to the request body until after
+ we have passed through the HTTP headers, and the HTTP message processor
+ is itself a filter in this model.
+ 
+ ....Roy
+ 
+ From dgaudet@arctic.org Thu Nov 18 17:25:06 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: dgaudet@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: bucket brigades and IOL
+ Date: 18 Nov 1999 06:47:20 +0100
+ Organization: Mail2News at engelschall.com
+ Lines: 23
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.20.9911171506480.32181-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 942904040 82793 141.1.129.1 (18 Nov 1999 05:47:20 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 18 Nov 1999 05:47:20 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:34101
+ 
+ 
+ 
+ On Sat, 13 Nov 1999, Ben Laurie wrote:
+ 
+ > Also, the usual objections still apply - i.e. it is awkward to do things
+ > like searching for particular strings, since they may cross boundaries.
+ > I'm beginning to think that the right answer to this is to provide nice
+ > matching functions that know about the chunked structures, and last
+ > resort functions that'll glue it all back into one chunk...
+ 
+ yeah, we use a zero-copy library at criticalpath and we frequently run
+ into the case where we want to do some string-like operation on data in
+ the zero-copy datastructure.  you end up having to either copy it to a
+ regular C string, or re-write all of the string functions.  consider
+ flex... or a regex library... neither work terribly well in the face of a
+ zero-copy abstraction because they don't have the equivalent of
+ writev()/readv().
+ 
+ but.  if apache had it, maybe we would see more libraries start to adopt
+ iovec-like interfaces... dunno.
+ 
+ Dean
+ 
+ From dgaudet@arctic.org Sat Nov 20 21:09:50 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: dgaudet@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: NO_WRITEV
+ Date: 20 Nov 1999 06:42:11 +0100
+ Organization: Mail2News at engelschall.com
+ Lines: 49
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.4.21.9911191106360.31086-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 943076531 76767 141.1.129.1 (20 Nov 1999 05:42:11 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 20 Nov 1999 05:42:11 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:34157
+ 
+ writev() allows us to reduce the number of packets on the network.
+ 
+ on linux we could use TCP_CORK and get the same effect with less code...
+ too bad linux is the only unix so far with this nice functionality.  
+ TCP_CORK is like the "other useful" setting other than nagle turned on...
+ with TCP_CORK, the kernel flushes any packets which fill an entire frame,
+ but holds partial packets until the socket is close()d or the cork is
+ removed.  in this way you can do multiple smaller write()s (or a write()
+ and a sendfile()) without causing small packets to go on the wire.
+ 
+ writev() may consume a small amount more cpu on the server, but it's my
+ opinion that this is a fine price to pay for fewer packets on the wire.
+ 
+ if you do choose to benchmark it, be sure to use slow modem clients, and
+ not fast lan clients... and give strong consideration to using client
+ latency as your metric rather than server cpu.
+ 
+ http://www.w3.org/Protocols/HTTP/Performance/Pipeline.html
+ 
+ Dean
+ 
+ On Fri, 19 Nov 1999, Eli Marmor wrote:
+ 
+ > Hello,
+ > 
+ > Is there any benchmark or statistics about how faster is Apache with
+ > writev in comparison to without it?  (i.e. a normal compilation under
+ > a platform supporting writev, vs. a compilation with "-DNO_WRITEV").
+ > 
+ > If there is no official benchmark, can anybody estimate the difference
+ > (in percents) under a typical use of Apache?  Does it depend on the
+ > type of use (static pages vs. dynamic, SSI and other parsings vs. one
+ > block, etc.)?  Or the other bottlenecks? (it makes sense that when
+ > your connection to the client is slow, you will not notice the
+ > difference between writing 2 buffers in two system calls or in one).
+ > 
+ > If there is a big difference, does it mean that Apache for non-writev 
+ > platforms (such as SCO, BeOS and Tandem) is slower and that these
+ > platforms are not recommended for Apache users?
+ > 
+ > On the other hand, if the difference is very small (let's say lower
+ > than 1%), maybe the benefits don't deserve the price (a much more
+ > complex code, especially when the non-writev code must be supported
+ > also in the future because of the non-writev platforms).
+ > 
+ > -- 
+ > Eli Marmor
+ > 
+ 
+ From dgaudet@arctic.org Mon Jun 28 19:06:50 1999
+ Path: engelschall.com!mail2news!apache.org!new-httpd-owner-rse+apache=en.muc.de
+ From: dgaudet@arctic.org (Dean Gaudet)
+ Newsgroups: en.lists.apache-new-httpd
+ Subject: Re: async routines
+ Date: 28 Jun 1999 17:33:24 +0200
+ Organization: Mail2News at engelschall.com
+ Lines: 96
+ Approved: postmaster@m2ndom
+ Message-ID: <Pine.LNX.3.96dg4.990628081527.31647G-100000@twinlark.arctic.org>
+ Reply-To: new-httpd@apache.org
+ NNTP-Posting-Host: en1.engelschall.com
+ X-Trace: en1.engelschall.com 930584004 99816 141.1.129.1 (28 Jun 1999 15:33:24 GMT)
+ X-Complaints-To: postmaster@engelschall.com
+ NNTP-Posting-Date: 28 Jun 1999 15:33:24 GMT
+ X-Mail2News-Gateway: mail2news.engelschall.com
+ Xref: engelschall.com en.lists.apache-new-httpd:31280
+ 
+ [hope you don't mind me cc'ing new-httpd zach, I think others will be
+ interested.]
+ 
+ On Mon, 28 Jun 1999, Zach Brown wrote:
+ 
+ > so dean, I was wading through the mpm code to see if I could munge the
+ > sigwait stuff into it.
+ > 
+ > as far as I could tell, the http protocol routines are still blocking.
+ > what does the future hold in the way for async routines? :)  I basically
+ > need a way to do something like..
+ 
+ You're still waiting for me to get the async stuff in there... I've done
+ part of the work -- the BUFF layer now supports non-blocking sockets. 
+ 
+ However, the HTTP code will always remain blocking.  There's no way I'm
+ going to try to educate the world in how to write async code... and since
+ our HTTP code has arbitrary call outs to third party modules... It'd
+ have a drastic effect on everyone to make this change.
+ 
+ But I honestly don't think this is a problem.  Here's my observations:
+ 
+ All the popular HTTP clients send their requests in one packet (or two
+ in the case of a POST and netscape).  So the HTTP code would almost
+ never have to block while processing the request.  It may block while
+ processing a POST -- something which someone else can worry about later,
+ my code won't be any worse than what we already have in apache.  So
+ any effort we put into making the HTTP parsing code async-safe would
+ be wasted on the 99.9% case.
+ 
+ Most responses fit in the socket's send buffer, and again don't require
+ async support.  But we currently do the lingering_close() routine which
+ could easily use async support.  Large responses also could use async
+ support.
+ 
+ The goal of HTTP parsing is to figure out which response object to
+ send.  In most cases we can reduce that to a bunch of common response
+ types:
+ 
+ - copying a file to the socket
+ - copying a pipe/socket to the socket  (IPC, CGIs)
+ - copying a mem region to the socket (mmap, some dynamic responses)
+ 
+ So what we do is we modify the response handlers only.  We teach them
+ about how to send async responses.
+ 
+ There will be a few new primitives which will tell the core "the response
+ fits one of these categories, please handle it".  The core will do the
+ rest -- and for MPMs which support async handling, the core will return
+ to the MPM and let the MPM do the work async...  the MPM will call a
+ completion function supplied by the core.  (Note that this will simplify
+ things for lots of folks... for example, it'll let us move range request
+ handling to a common spot so that more than just default_handler
+ can support it.)
+ 
+ I expect this to be a simple message passing protocol (pass by reference).
+ Well rather, that's how I expect to implement it in ASH -- where I'll
+ have a single thread per-process doing the select/poll stuff; and the
+ other threads are in a pool that handles the protocol stuff.  For your
+ stuff you may want to do it another way -- but we'll be using a common
+ structure that the core knows about... and that structure will look like
+ a message:
+ 
+     struct msg {
+        enum {
+            MSG_SEND_FILE,
+            MSG_SEND_PIPE,
+            MSG_SEND_MEM,
+            MSG_LINGERING_CLOSE,
+            MSG_WAIT_FOR_READ,  /* for handling keep-alives */
+            ...
+        } type;
+        BUFF *client;
+        void (*completion)(struct msg *, int status);
+        union {
+            ... extra data here for whichver types need it ...;
+        } x;
+     };
+ 
+ The nice thing about this is that these operations are protocol
+ independant... at this level there's no knowledge of HTTP, so the same
+ MPM core could be used to implement other protocols.
+ 
+ > so as I was thinking about this stuff, I realized it might be neat to have
+ > 'classes' of non blocking pending work and have different threads with
+ > differnt priorities hacking on it.  Say we have a very high priority
+ > thread that accepts connectoins, does initial header parsing, and
+ > sendfile()ing data out.  We could have lower priority threads that are
+ > spinning doing 'harder' BUFF work like an encryption layer or gziping
+ > content, whatever.
+ 
+ You should be able to implement this in your MPM easily I think... because
+ you'll see the different message types and can distribute them as needed.
+ 
+ Dean
+ 


ossp-pkg/sio/BRAINSTORM/doc_SFmtg.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
--- -    Wed May  8 23:36:30 2024
***************
*** 0 ****
--- 1,172 ----
+ 
+ From akosut@leland.Stanford.EDU Thu Jul 23 09:38:40 1998
+ Date: Sun, 19 Jul 1998 00:12:37 -0700 (PDT)
+ From: Alexei Kosut <akosut@leland.Stanford.EDU>
+ To: new-httpd@apache.org
+ Subject: Apache 2.0 - an overview
+ 
+ For those not at the Apache meeting in SF, and even for those who were,
+ here's a quick overview of (my understanding of) the Apache 2.0
+ architecture that we came up with. I present this to make sure that I have
+ it right, and to get opinions from the rest of the group. Enjoy.
+ 
+ 
+ 1. "Well, if we haven't released 2.0 by Christmas of 1999, it won't
+     matter anyway." 
+ 
+ A couple of notes about this plan: I'm looking at this right now from a
+ design standpoint, not an implementation one. If the plan herein were
+ actually coded as-is, you'd get a very inefficient web server. But as
+ Donald Knuth (Professor emeritus at Stanford, btw... :) points out,
+ "premature optimization is the root of all evil." Rest assured there are
+ plenty of ways to make sure Apache 2.0 is much faster than Apache 1.3.
+ Taking out all the "slowness" code, for example... :)
+ 
+ Also, the main ideas in this document mainly come from Dean Gaudet, Simon
+ Spero, Cliff Skolnick and a bunch of other people, from the Apache Group's
+ meeting in San Francisco, July 2 and 3, 1998. The other ideas come from
+ other people. I'm being vague because I can't quite remember. We should
+ have videotaped it.  I've titled the sections of this document with quotes
+ from our meeting, but they are paraphrased from memory, so don't take them
+ too seriously.
+ 
+ 2. "But Simon, how can you have a *middle* end?"
+ 
+ One of the main goals of Apache 2.0 is protocol independence (i.e.,
+ serving HTTP/1.1, HTTP-NG, and maybe FTP or gopher or something). Another
+ is to rid the server of the belief that everything is a file. Towards this
+ end, we divide the server up into three parts, the front end, the middle
+ end, and the back end.
+ 
+ The front end is essentially a combination of http_main and http_protocol
+ today. It takes care of all network and protocol matters, interpreting the
+ request, putting it into a protocol-neutral form, and (possibly) passing
+ it off to the rest of the server. This is approximately equivalent to the
+ part of Apache contained in Dean's flow stuff, and it also works very well
+ in certain non-Unix-like architectures such as clustered mainframes. In
+ addition, part of this front-end might be optionally run in kernel space,
+ giving a very fast server indeed...
+ 
+ The back end is what generates the content. At the back of the back end we
+ have backing stores (Cliff's term), which contain actual data. These might
+ represent files on a disk, entries in a database, CGI scripts, etc... The
+ back end also consists of other modules, which can alter the request in
+ various fashions. The objects the server acts on can be thought of (Cliff
+ again) as a filehandle and a set of key/value pairs (metainformation).
+ The modules are set up as filters that can alter either one of those,
+ stacking I/O routines onto the stream of data, or altering the
+ metainformation.
+ 
+ The middle end is what comes between the front and back ends. Think of
+ http_request. This section takes care of arranging the modules, backing
+ stores, etc... into a manner so that the path of the request will result
+ in the correct entity being delivered to the front end and sent to the
+ client.
+ 
+ 3. "I won't embarrass you guys with the numbers for how well Apache
+     performs compared to IIS." (on NT)
+ 
+ For a server that was designed to handle flat files, Apache does it
+ surprisingly poorly, compared with other servers that have been optimized
+ for it. And the performance for non-static files is, of course, worse.
+ While Apache is still more than fast enough for 95% of Web servers, we'd
+ be remiss to dismiss those other 5% (they're the fun ones anyway). Another
+ problem Apache has is its lack of a good, caching, proxy module.
+ 
+ Put these together, along with the work Dean has done with the flow and
+ mod_mmap_static stuff, and we realize the most important part of Apache
+ 2.0: a built-in, all-pervasive, cache. Every part of the request process
+ will involve caching. In the path outlined above, between each layer of
+ the request, between each module, sits the cache, which can (when it is
+ useful), cache the response and its metainformation - including its
+ variance, so it knows when it is safe to give out the cached copy. This
+ gives every opportunity to increase the speed of the server by making sure
+ it never has to dynamically create content more than it needs to, and
+ renders accelerators such as Squid unnecessary.
+ 
+ This also allows what I alluded to earlier: a kernel (or near-to-kernel)
+ based web server component, which could read the request, consult the
+ cache to find the requested object, and spit it back out, without so much
+ as an interrupt in the way. Of course, the rest of Apache (with all its
+ modules - it's generally a bad idea to let unknown, untrusted code, insert
+ itself into the kernel) sits up in user-space, ready to handle any request
+ the micro-Apache can't.
+ 
+ A built-in cache also makes a real working HTTP/1.1 proxy server trivially
+ easy to write.
+ 
+ 4. "Stop asking about backwards compatibility with the API. We'll write a
+     compatibility module... later." 
+ 
+ If modules are as described above, then obviously they are very much
+ distinct from how Apache's current modules function. The only module
+ function that is similar to the current model is the handler, or backing
+ store, that actually provides the basic stream of data that the server
+ alters to product a response entity.
+ 
+ The basic module's approach to its job is to stack a filter onto the
+ output. But it's better to think of the modules not as a stack that the
+ request flows through (a layer cake with cache icing between the layers),
+ but more of a mosaic (pretend I didn't use that word. I wrote collage. You
+ can't prove anything), with modules stuck onto various sides of the
+ request at different points, altering the request/response.
+ 
+ Today's Apache modules take an all-or-nothing approach to request
+ handlers. They tell Apache what they can do, overestimating, and then are
+ supposed to DECLINE if they don't pass a number of checks they are
+ supposed to make. Most modules don't do this correctly. The better
+ approach is to allow the modules to inform Apache exactly of what they can
+ do, and have Apache (the middle-end) take care of invoking them when
+ appropriate.
+ 
+ The final goal of all of this, of course, is simply to allow CGI output to
+ be parsed for server-side includes. But don't tell Dean that.
+ 
+ 5. "Will Apache run without any of the normal Unix binaries installed,
+     only the BSD/POSIX libraries?"
+ 
+ Another major issue is, of course, configuration of the server. There are
+ a number of distinct opinions on this, both as to what should be
+ configured and how it should be done. We talked mainly about the latter,
+ but the did touch on the former. Obviously, with a radically distinct
+ module API, the configuration is radically different. We need a good way
+ to specify how the modules are supposed to interact, and of controlling
+ what they can do, when and how, balancing what the user asks the server to
+ do, and what the module (author) wants the server to do. We didn't really
+ come up with a good answer to this.
+ 
+ However, we did make some progress on the other side of the issue: We
+ agreed that the current configuration system is definitely taking the
+ right approach. Having a well-defined repository of the configuration
+ scheme, containing the possible directives, when they are applicable, what
+ their parameters are, etc... is the right way to go. We agreed that more
+ information and stronger-typing (no RAW_ARGS!) would be good, and may
+ enable on-the-fly generated configuration managers.
+ 
+ We agreed that such a program, probably external to Apache, would generate
+ a configuration and pass it to Apache, either via a standard config file,
+ or by calling Apache API functions. It is desirable to be able to go the
+ other way, pulling current configuration from Apache to look at, and
+ perhaps change it on the fly, but unfortunately is unlikely this
+ information would always be available; modules may perform optimizations
+ on their configuration that makes the original configuration unavailable.
+ 
+ For the language and specification of the configuration, we thought
+ perhaps XML might be a good approach, and agreed it should be looked
+ into. Other issues, such as SNMP, were brought up and laughed at.
+ 
+ 6. "So you're saying that the OS that controls half the banks, and 90% of
+     the airlines, doesn't even have memory protection for seperate
+     processes?"
+ 
+ Obviously, there are a lot more items that have to be part of Apache 2.0,
+ and we talked about a number of them. However, the four points above, I
+ think, represent the core of the architecture we agreed on as a starting
+ point.
+ 
+ -- Alexei Kosut <akosut@stanford.edu> <http://www.stanford.edu/~akosut/>
+    Stanford University, Class of 2001 * Apache <http://www.apache.org> *
+ 
+ 
+ 
+ 


ossp-pkg/sio/BRAINSTORM/doc_bucket_brigades.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
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***************
*** 0 ****
--- 1,381 ----
+ To: new-httpd@apache.org
+ Subject: bucket brigades and IOL
+ Date: Fri, 12 Nov 1999 23:57:43 -0800
+ From: "Roy T. Fielding" <fielding@kiwi.ICS.UCI.EDU>
+ Message-ID:  <199911122357.aa18914@gremlin-relay.ics.uci.edu>
+ 
+ About two years ago I wasted a lot of time writing an Ada95 library
+ called Onions that provides a stackable stream abstraction for files,
+ sockets, etc.  It is at <http://www.ics.uci.edu/pub/websoft/libwww-ada95/>
+ if you want to take a look at it, but I don't recommend looking at the
+ code since it is almost all just working around Ada95's lack of a
+ system interface.  I'll describe the worthwhile bits here.
+ 
+ The heart of Onions is the input and output stream object
+ classes and classwide types for building a data stream via a
+ stack of stream objects (Input_Pipe and Output_Pipe).  Reading
+ from the head of an input pipe causes the head stream object
+ to read from the next outbound stream object, and on down the line.
+ Likewise for writing to the head of an output pipe.  One of the
+ main features of streams is that they can filter the data as it
+ passes, converting, adding to, and/or removing from the data
+ before giving it to the next object.  Since multiple streams can be
+ cascaded, the complete data conversion is the sum of the individual
+ data conversions performed by the stream objects.
+ 
+ So far, no big deal -- this can be manually created by stacking ap_iol
+ types in a meaningful way.  But, the one unique thing I did in Onions was 
+ abstract the memory handling into something called Buckets and moved them
+ around in Bucket_Brigades.  A bucket is an allocated segment of memory
+ with pointers to its allocation address and current size.  If I were doing
+ this in C, I'd also add a pointer to current start address and allocated
+ size, so that a single bucket could be shrunk from both ends without
+ copying, and a function pointer for freeing it at the stream end.
+ Note that this is the same type of memory structure that IO-Lite uses,
+ though developed independently and for different reasons.
+ 
+ A bucket brigade is a list-queue of buckets.  Each of the stream read/write
+ calls would pass a bucket brigade instead of single bucket, since this
+ made insertion by filters more efficient, with the general idea being that
+ the outbound end of the sream would be writing them out using writev
+ or reading them in using readv, which is about as efficient as I could
+ get with Ada95.  [I call it a list-queue instead of just queue because you
+ have the choice of removing buckets from (or adding to) the queue one
+ bucket at a time or an entire linked list of buckets.]
+ 
+ But we could go one step further.  A bucket is an ADT, and as such can
+ be used as a general handle for read-only memory, read-write memory,
+ cache object, file handle, mmap handle, file name, URL, whatever.
+ What if, instead of just a stream of memory, it could pass around a
+ stream of memory interspersed with file handles or references to
+ remote objects?  A filter could then add stuff around the stream without
+ causing too much parsing overhead, and if it needed to look at all the
+ bytes in the stream it would just replace the bucket handle with a stream
+ of memory sucked from that handle.  Something like this was talked about
+ last year (see threads on "Stacking up Response Handling" on 23 Sep 1998
+ and "I/O filters & reference counts" in late December 1998 and January 1999).
+ And Dean started something with ap_buf.h, but I don't know how he meant
+ to finish it.
+ 
+ What I was thinking of was
+ 
+    typedef enum {
+        AP_BUCKET_rwmem,
+        AP_BUCKET_rmem,
+        AP_BUCKET_file_t,
+        AP_BUCKET_mmap_t,
+        AP_BUCKET_filename,
+        AP_BUCKET_cached_entity,
+        AP_BUCKET_URI,
+    } ap_bucket_color_t;
+ 
+    typedef struct ap_bucket_t ap_bucket_t;
+    struct ap_bucket_t {
+        ap_bucket_color_t color;
+        void              *content;
+        ap_status_t       (*free)(ap_bucket_t *bucket);
+        unsigned int      refcount;
+    };
+ 
+    typedef struct ap_bucket_rwmem_t ap_bucket_rwmem_t;
+    struct ap_bucket_rwmem_t {
+        void   *alloc_addr;
+        size_t  alloc_len;
+        void   *addr;
+        size_t  len;
+    };
+ 
+    typedef struct ap_bucket_rmem_t ap_bucket_rmem_t;
+    struct ap_bucket_rmem_t {
+        void   *addr;
+        size_t  len;
+    };
+ 
+    typedef struct ap_bucket_filename ap_bucket_filename;
+    struct ap_bucket_filename {
+        ap_context_t *ctx;
+        char         *name;
+        ap_stat_t    *stat;  /* useful if already stat'ed */
+        ap_aa_t      *conf;  /* access control structure for this file */
+    };
+ 
+    ...
+ 
+ and then
+ 
+    typedef struct ap_bucket_list_t ap_bucket_list_t;
+    struct ap_bucket_list_t {
+        ap_bucket_t *bucket;
+        ap_bucket_list_t *prev;
+        ap_bucket_list_t *next;
+    };
+ 
+    typedef struct ap_brigade_t ap_brigade_t;
+    struct ap_brigade_t {
+        ap_context_t     *ctx;
+        ap_bucket_list_t *first;
+        ap_bucket_list_t *last;
+        unsigned int     count;
+    };
+ 
+ and then construct the input and output streams as pushing these
+ bucket brigades to or from the client.  The streams would have to
+ be a little more complicated than Onions, since I learned later that
+ you also need a parallel stream of header fields (in tokenized form)
+ in order for it to work with anything HTTP-like.
+ 
+ Why use an enum instead of a bunch of file pointers for each type
+ of bucket, kind of like ap_iol?  Because it allows adjacent memory
+ buckets (the most frequent kind after a filter operation) to be
+ gathered into a single writev.  Also, we need a way to be able to
+ set up an operation and figure out what it will produce without
+ actually performing the operation -- this is for OPTIONS and HEAD.
+ 
+ Note that this would completely change the way we handle internal
+ redirects, subrequests, server-side include, mod_proxy, access control, etc.
+ And then most of the API hooks would need to change.  I think that is why
+ Dean was putting it off until 2.1.  The annoying thing is that this is the
+ most useful rearchitecting of the server -- the MPM, APR, and hook changes
+ make 2.0 easier/cleaner/faster to port to other platforms, but layering
+ enables in one fell swoop almost every significant non-config feature
+ that our users have requested.  A cache would just be a hash table or
+ btree of file buckets, complete with AA info.
+ 
+ Anyway, that was stuck in the back of my head and had to get out.
+ I won't be able to work on it until after the dissertation is done,
+ which every day seems to be further away.  Maybe 3.0, with rHTTP/2.0.
+ 
+ ....Roy
+ 
+ =================================================
+ To: new-httpd@apache.org
+ Subject: Re: bucket brigades and IOL
+ In-reply-to: Your message of "Sat, 13 Nov 1999 20:43:58 GMT."
+              <382DCD8E.881B8468@algroup.co.uk>
+ Date: Sun, 14 Nov 1999 22:24:03 -0800
+ From: "Roy T. Fielding" <fielding@kiwi.ICS.UCI.EDU>
+ Message-ID:  <199911142224.aa22545@gremlin-relay.ics.uci.edu>
+ 
+ BenL wrote:
+ >I've got to say that this is the most coherent suggestion along these
+ >lines that I've seen yet. I rather like it. One thing I'd add is that if
+ >you are going to have a movable "start of block" pointer, and changeable
+ >length, it can be nice to allocate extra around the edges under some
+ >circumstances, so that lower layers can expand the block without having
+ >to add extra chunks.
+ 
+ Or, alternatively, allocate equal size blocks and just pass around
+ a reference pair within the buckets that, when the bucket is freed,
+ access a more complicated reference-counting pool.  I think that is
+ closer to what IO-Lite does.
+ 
+ >Also, the usual objections still apply - i.e. it is awkward to do things
+ >like searching for particular strings, since they may cross boundaries.
+ >I'm beginning to think that the right answer to this is to provide nice
+ >matching functions that know about the chunked structures, and last
+ >resort functions that'll glue it all back into one chunk...
+ 
+ Yep, that's what I ended up doing for Ada95, though in that case there
+ were no easier alternatives.
+ 
+ ....Roy
+ 
+ =================================================
+ To: new-httpd@apache.org
+ Subject: Re: layered I/O (was: cvs commit: ...) 
+ In-reply-to: Your message of "Wed, 29 Mar 2000 01:21:09 PST."
+              <Pine.LNX.4.21.0003290004100.10357-100000@piglet> 
+ Date: Wed, 29 Mar 2000 02:05:08 -0800
+ From: "Roy T. Fielding" <fielding@kiwi.ICS.UCI.EDU>
+ Message-ID:  <200003290205.aa19557@gremlin-relay.ics.uci.edu>
+ 
+ >Selection of IO Layers
+ >
+ >The core selects a source module and IO layers based on the urlspace
+ >configuration.  Content might be generated by mod_perl, and the result is
+ >piped through mod_chunk, mod_ssl, and mod_net, in turn.  When the content
+ >generator runs, the core enforces that the module set the content type
+ >before the first call to ap_bput.  The content type is set by a function
+ >call.  The function (ap_set_content_type(request_rec *, char *)) examines
+ >the content type and adds IO layers as neccessary.  For server parsed
+ >html, the core might insert mod_include immediately after mod_perl.
+ 
+ The problem of thinking of it that way is that, like Dean mentioned,
+ the output of one module may be filtered and the filter indicate that
+ content should be embedded from another URL, which turns out to be a
+ CGI script that outputs further parseable content.  In this instance,
+ the goal of layered-IO is to abstract away such behavior so that the
+ instance is processed recursively and thus doesn't result in some tangled
+ mess of processing code for subrequests.  Doing it requires that each
+ layer be able to pass both data and metadata, and have both data and
+ metadata be processed at each layer (if desired), rather than call a
+ single function that would set the metadata for the entire response.
+ 
+ My "solution" to that is to pass three interlaced streams -- data,
+ metadata, and meta-metadata -- through each layer.  The metadata
+ streams would point to a table of tokenized name-value pairs.
+ There are lots of ways to do that, going back to my description of
+ bucket brigades long ago.  Basically, each block of memory would
+ indicate what type of data, with metadata occurring in a block before
+ the data block(s) that it describes (just like chunk-size describes
+ the subsequent chunk-data) and the layers could be dynamically
+ rearranged based on the metadata that passed through them, in
+ accordance with the purpose of the filter.
+ 
+ >(Can anyone produce a use case where the IO chain could change after
+ >output begins?)
+ 
+ Output is a little easier, but that is the normal case for input.
+ We don't know what filters to apply to the request body until after
+ we have passed through the HTTP headers, and the HTTP message processor
+ is itself a filter in this model.
+ 
+ ....Roy
+ 
+ 
+ =================================================
+ To: new-httpd@apache.org
+ Subject: Re: filtering patches
+ In-reply-to: Your message of "Mon, 10 Jul 2000 15:33:25 PDT."
+              <Pine.LNX.4.21.0007101528180.10878-100000@koj.rkbloom.net>
+ Date: Mon, 10 Jul 2000 16:58:00 -0700
+ From: "Roy T. Fielding" <fielding@kiwi.ICS.UCI.EDU>
+ Message-ID:  <200007101657.aa21782@gremlin-relay.ics.uci.edu>
+ 
+ [...]
+ I meant that the filters, when written to as part of the output stream,
+ are treated as a stack (write to the top-most filter without any knowledge
+ of what may lie underneath it).  So the process of arranging filters
+ for a particular response is like dropping them onto a stack.  When a
+ filter is done or the stream is closed, each instantiated filter cleans
+ up according to its local state and then destroys itself (as it is popped
+ off the stack).
+ 
+ This is completely separate from the registration of filters by
+ name and purpose, which could be done by hooks.  The difference is that
+ filters are registered at config time but only instantiated (given local
+ storage) and arranged on a per stream basis.
+ 
+ Bucket brigades is simply a way to encapsulate and pass data down the stream
+ such that it can be as efficient as the sender desires, while retaining
+ a simple interface.  The purpose of the bucket is to make handling of the
+ data uniform regardless of its type, or make type-specific conversions
+ via a single ADT call if and only if they are needed by some filter.
+ The purpose of the brigade is to reduce the number of calling arguments
+ and linearize the calling sequence for insertion filters.  Each filter
+ definition is separate from its instantiation on the stream because
+ there may be many streams operating at once within a single program.
+ Each bucket is independent of the brigade so that the filters can rearrange
+ and insert buckets at will.  Each data item is isolated by the bucket
+ structure, which allows them to be split across child buckets or shared
+ with multiple streams (e.g., cached objects).  We don't need to implement
+ all of this on the first pass -- we just need to implement the ADT external
+ interfaces such that they don't have to change as we make the overall
+ stream more efficient.
+ 
+ BTW, in case I didn't make this clear in past messages, this design is
+ an amalgam of the best aspects of the designs from Henrik's Streams
+ (see w3c-libwww), sfio (AT&T Research), IO-Lite (Rice Univ.), and
+ libwww-ada95 (UCI).  The MIME stuff in MSIE is based on Henrik's streams.
+ Henrik's stuff is very fast, but is spaghetti code because it relies on
+ callbacks and legacy stuff in libwww.  sfio is great but is intended to
+ be a complete replacement for stdio and hence does way too much and is
+ subject to a few patents that I don't appreciate.  IO-Lite is cool but
+ is probably only worth it when the entire OS is based on IO-Lite memory
+ management, but regardless the code isn't available for commercial use.
+ As Dean has mentioned many times, we already get most of the performance
+ benefit of IO-Lite simply by avoiding memory copies on large writes.
+ libwww-ada95 was an attempt to make Ada95 suck less for systems programming,
+ which was only a partial success (it is very fast compared to other Ada95
+ libraries, but memory management became a problem with complex filters).
+ 
+ Writing our own streams library isn't NIH syndrome -- both Dean and I
+ have independently investigated the other available alternatives and they
+ just aren't suitable for our purpose.  Even with all that, my own design
+ only truly pays off (versus plain old BUFF) when you make good use of
+ sendfile and shared object caching.
+ 
+ [...]
+ 
+ 
+ =================================================
+ Other stuff Roy wrote on new-httpd:
+ 
+ My buckets are passed around in list-queues (really just lists with front
+ and back pointers).  My buckets carry data and metadata and meta-metadata.
+ My buckets are used to indicate stream-end, and the filter configuration
+ itself is determined by the stream content.  It probably sounds weird, but
+ the effects of this interface are completely different than mere content
+ filters.  They simplify everything.  I'm not saying that we have to
+ simplify everything right away, but I am saying that it is just as easy
+ to implement a fully-general filter using bucket brigades as it is
+ to implement string interface filters -- all of the complex parts
+ are handled by the ADTs.
+ 
+ ...
+ 
+ The real psychedelic stuff happens when you can pass metadata (tokenized
+ header fields) as buckets and the filters know how to pass that down the
+ chain without treating them as data.
+ 
+ ...
+ 
+ The purpose of passing a list of buckets around is to linearize
+ the call stack for the frequent case of filtered content
+ splitting one large bucket into separate buckets with filtered results
+ interspersed in between.  The effect is that a filter chain can frequently
+ process an entire message in one pass down the chain, which enables the
+ stream end to send the entire response in one go, which also allows it
+ to do interesting things like provide a content length by summing the
+ data length of all the buckets' data, and set a last-modified time
+ by picking the most recent time from a set of static file buckets.
+ 
+ I think it would help if we stopped using artificial examples.  Let's
+ try something simple:
+ 
+        socket <-- http <-- add_footer <-- add_header <-- send_file
+ 
+ send_file calls its filter with an ap_file_t bucket and End-of-Stream (EOS)
+ in the bucket list.  add_header sets a flag, prepends another ap_file_t
+ bucket to the list and sends the list to its filter.  add_footer looks
+ at the list, finds the EOS, inserts another ap_file_t bucket in
+ front of the EOS, and sends the list on to its filter.  http walks through
+ the list picking up the (cached) stat values, notes the EOS and seeing
+ that its own flag for headers_sent is false, sets the cumulative metadata
+ and sends the header fields, followed by three calls to the kernel to
+ send out the three files using whatever mechanism is most efficient.
+ 
+ The point here isn't that this is the only way to implement filters.
+ The point is that no other interface can implement them as efficiently.
+ Not even close.  Yes, there are cases where string filters are just as
+ efficient as any other design, but there is no case in which they are
+ more efficient than bucket brigades.  The reason is that being able
+ to process a list of strings in one call more than offsets the extra
+ cost of list processing, regardless of the filter type, and allows
+ for additional features that have benefits for http processing.
+ Like, for example, being able to determine the entire set of resources
+ that make up the source of this dynamic resource without teaching every
+ filter about WebDAV.
+ 
+ ...
+ 
+ Making many small calls down the filter chain is something best
+ avoided, which is why the bucket brigades interface consists of
+ a linked list of buckets, such that all of the currently available
+ data can be passed-on in a single call.
+ 
+ Being able to handle sendfile, cached objects and subrequests is very
+ effective at improving efficiency, which is why the buckets are typed.
+ A filter that needs to do byte-level processing will have to call a
+ routine to convert the typed bucket into a data stream, but that decision
+ is delayed until no other choice is available and adds no overhead to
+ the common cases of non-filtered or pre-/post-filtered objects.
+ 
+ Being able to process header fields (metadata) through the same filter
+ set as the data is necessary for correctness and simplicity in the
+ proper ordering of independently developed filter modules, which is
+ why the buckets can carry metadata on the same stream.  Every filter
+ has to be knowledgeable about metadata because only the filter knows
+ whether or not its actions will change the nature of the data.
+ 
+ 


ossp-pkg/sio/BRAINSTORM/doc_dean_iol.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
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***************
*** 0 ****
--- 1,496 ----
+ goals? we need an i/o abstraction which has these properties:
+ 
+ - buffered and non-buffered modes
+ 
+     The buffered mode should look like FILE *.
+ 
+     The non-buffered mode should look more like read(2)/write(2).
+ 
+ - blocking and non-blocking modes
+ 
+     The blocking mode is the "easy" mode -- it's what most module writers
+     will see.  The non-blocking mode is the "hard" mode, this is where
+     module writers wanting to squeeze out some speed will have to play.
+     In order to build async/sync hybrid models we need the
+     non-blocking i/o abstraction.
+ 
+ - timed reads and writes (for blocking cases)
+ 
+     This is part of my jihad against asynchronous notification.
+ 
+ - i/o filtering or layering
+ 
+     Yet another Holy Grail of computing.  But I digress.  These are
+     hard when you take into consideration non-blocking i/o -- you have
+     to keep lots of state.  I expect our core filters will all support
+     non-blocking i/o, well at least the ones I need to make sure we kick
+     ass on benchmarks.  A filter can deny a switch to non-blocking mode,
+     the server will have to recover gracefully (ha).
+ 
+ - copy-avoidance
+ 
+     Hey what about zero copy a la IO-Lite?  After having experienced it
+     in a production setting I'm no longer convinced of its benefits.
+     There is an enormous amount of overhead keeping lists of buffers,
+     and reference counts, and cleanup functions, and such which requires
+     a lot of tuning to get right.  I think there may be something here,
+     but it's not a cakewalk.
+ 
+     What I do know is that the heuristics I put into apache-1.3 to choose
+     writev() at times are almost as good as what you can get from doing
+     full zero-copy in the cases we *currently* care about.  To put it
+     another way, let's wait another generation to deal with zero copy.
+ 
+     But sendfile/transmitfile/etc. those are still interesting.
+ 
+     So instead of listing "zero copy" as a property, I'll list
+     "copy-avoidance".
+ 
+ So far?
+ 
+ - ap_bungetc added
+ - ap_blookc changed to return the character, rather than take a char *buff
+ - in theory, errno is always useful on return from a BUFF routine
+ - ap_bhalfduplex, B_SAFEREAD will be re-implemented using a layer I think
+ - chunking gone for now, will return as a layer
+ - ebcdic gone for now... it should be a layer
+ 
+ - ap_iol.h defined, first crack at the layers...
+ 
+     Step back a second to think on it.  Much like we have fread(3)
+     and read(2), I've got a BUFF and an ap_iol abstraction.  An ap_iol
+     could use a BUFF if it requires some form of buffering, but many
+     won't require buffering... or can do a better job themselves.
+ 
+     Consider filters such as:
+        - ebcdic -> ascii
+        - encryption
+        - compression
+     These all share the property that no matter what, they're going to make
+     an extra copy of the data.  In some cases they can do it in place (read)
+     or into a fixed buffer... in most cases their buffering requirements
+     are different than what BUFF offers.
+ 
+     Consider a filter such as chunking.  This could actually use the writev
+     method to get its job done... depends on the chunks being used.  This
+     is where zero-copy would be really nice, but we can get by with a few
+     heuristics.
+ 
+     At any rate -- the NSPR folks didn't see any reason to included a
+     buffered i/o abstraction on top of their layered i/o abstraction... so
+     I feel like I'm not the only one who's thinking this way.
+ 
+ - iol_unix.c implemented... should hold us for a bit
+ 
+ 
+ ==============================
+ Date: Mon, 10 Apr 2000 14:39:48 -0700 (PDT)
+ From: dean gaudet <dgaudet-list-new-httpd@arctic.org>
+ To: new-httpd@apache.org
+ Subject: Re: Buff should be an I/O layer
+ In-Reply-To: <20000410123109.C3931@manojk.users.mindspring.com>
+ Message-ID: <Pine.LNX.4.21.0004101418410.2626-100000@twinlark.arctic.org>
+ 
+ [hope you don't mind me taking this back to new-httpd so that it's
+ archived this time :)]
+ 
+ On Mon, 10 Apr 2000, Manoj Kasichainula wrote:
+ 
+ > On Mon, Mar 27, 2000 at 04:48:23PM -0800, Dean Gaudet wrote:
+ > > On Sat, 25 Mar 2000, Manoj Kasichainula wrote:
+ > > > (aside: Though my unschooled brain still sees no
+ > > > problem if our chunking layer maintains a pile of 6-byte blocks that
+ > > > get used in an iol_writev. I'll read the archived discussions.)
+ > > 
+ > > there's little in the way of archived discussions, there's just me admitting
+ > > that i couldn't find a solution which was not complex.
+ > 
+ > OK, there's got to be something wrong with this:
+ > 
+ > chunk_iol->iol_write(char *buffer) {
+ >     pull a 10-byte (or whatever) piece out of our local stash
+ >     construct a chunk header in it
+ >     set the iovec = chunk header + buffer
+ >     writev(iovec)
+ > }
+ > 
+ > But what is it?
+ 
+ when i was doing the new apache-2.0 buffering i was focusing a lot on
+ supporting non-blocking sockets so we could do the async i/o stuff -- and
+ to support a partial write you need to keep more state than what your
+ suggestion has.
+ 
+ also, the real complexity comes when you consider handling a pipelined
+ HTTP/1.1 connection -- consider what happens when you get 5 requests
+ for /cgi-bin/printenv smack after the other.
+ 
+ if you do that against apache-1.3 and the current apache-2.0 you get
+ back maximally packed packets.  but if you make chunking a layer then
+ every time you add/remove the layer you'll cause a packet boundary --
+ unless you add another buffering layer... or otherwise shift around
+ the buffering.
+ 
+ as a reminder, visit
+ <http://www.w3.org/Protocols/HTTP/Performance/Pipeline.html> for a
+ description of how much we win on the wire from such an effort.
+ 
+ also, at some point i worry that passing the kernel dozens of tiny
+ iovecs is more expensive than an extra byte copy into a staging buffer,
+ and passing it one large buffer.  but i haven't done any benchmarks to
+ prove this.  (my suscipions have to do with the way that at least the
+ linux kernel's copying routine is written regarding aligned copies)
+ 
+ oh it's totally worth pointing out that at least Solaris allows at
+ most 16 iovecs in a single writev()... which probably means every sysv
+ derived system is similarly limited.  linux sets the limit at 1024.
+ freebsd has an optimisation for up to 8, but otherwise handles 1024.
+ 
+ i'm still doing work in this area though -- after all my ranting about
+ zero-copy a few weeks back i set out to prove myself wrong by writing
+ a zero-copy buffering library using every trick in my book.  i've no
+ results to share yet though.
+ 
+ -dean
+ 
+ 
+ ==============================
+ Date: Tue, 2 May 2000 15:51:30 +0200
+ From: Martin Kraemer <Martin.Kraemer@mch.sni.de>
+ To: new-httpd@apache.org
+ Subject: BUFF, IOL, Chunking, and Unicode in 2.0 (long)
+ Message-ID: <20000502155129.A10548@pgtm0035.mch.sni.de>
+ 
+ Sorry for a long silence in the past weeks, I've been busy with other
+ stuff.
+ 
+ Putting the catch-words "Chunking, Unicode and 2.0" into the subject
+ was on purpose: I didn't want to scare off anyone because of the word
+ EBCDIC: the problems I describe here, and the proposed new buff.c
+ layering, are mostly independent from the EBCDIC port.
+ 
+ 
+ In the past weeks, I've been thinking about today's buff.c (and
+ studied its applicability for automatic conversion stuff like in the
+ russian apache, see apache.lexa.ru). I think it would be neat to be
+ able to do automatic character set conversion in the server, for
+ example by negotiation (when the client sends an Accept-Charset and
+ the server doesn't have a document with exactly the right Charset, but
+ knows how to generate it from an existing representation).
+ 
+ IMO it is a reoccurring problem,
+ 
+ * not only in today's russian internet environment (de facto browsers
+   support 5 different cyrillic character sets, but the server doesn't
+   want to hold every document in 5 copies, so an automatic translation
+   is performed by the russian apache, depending on information supplied
+   by the client, or by explicit configuration). One of the supported
+   character sets is Unicode (UTF-7 or UTF-8)
+ 
+ * in japanese/chinese environments, support for 16 bit character sets
+   is an absolute requirement. (Other oriental scripts like Thai get
+   along with 8 bit: they only have 44 consonants and 16 vowels).
+   Having success on the eastern markets depends to a great deal on
+   having support for these character sets. The japanese Apache
+   community hasn't had much contact with new-httpd in the past, but
+   I'm absolutely sure that there is a "standard japanese patch" for
+   Apache which would well be worth integrating into the standard
+   distribution. (Anyone on the list to provide a pointer?)
+ 
+ * In the future, more and more browsers will support unicode, and so
+   will the demand grow for servers supporting unicode. Why not
+   integrate ONE solution for the MANY problems worldwide?
+ 
+ * The EBCDIC port of 1997 has been a simple solution for a rather
+   simple problem. If we would "do it right" for 2.0 and provide a
+   generic translation layer, we would solve many problems in a single
+   blow. The EBCDIC translation would be only one of them.
+ 
+ Jeff has been digging through the EBCDIC stuff and apparently
+ succeeded in porting a lot of the 1.3 stuff to 2.0 already. Jeff, I'd
+ sure be interested in having a look at it. However, when I looked at
+ buff.c and the new iol_* functionality, I found out that iol's are not
+ the way to go: they give us no solution for any of the conversion
+ problems:
+ 
+ * iol's sit below BUFF. Therefore, they don't have enough information
+   to know which part of the written byte stream is net client data,
+   and which part is protocol information (chunks, MIME headers for
+   multipart/*).
+ 
+ * iol's don't allow simplification of today's chunking code. It is
+   spread thruout buff.c and there's a very hairy balance between
+   efficiency and code correctness. Re-adding (EBCDIC/UTF) conversion,
+   possibly with sup[port for multi byte character sets (MBCS), would
+   make a code nightmare out of it. (buff.c in 1.3 was "almost" a
+   nightmare because we had onlu single byte translations.
+ 
+ * Putting conversion to a hierarchy level any higher than buff.c is no
+   solution either: for chunks, as well as for multipart headers and
+   buffering boundaries, we need character set translation. Pulling it
+   to a higher level means that a lot of redundant information has to
+   be passed down and up.
+ 
+ In my understanding, we need a layered buff.c (which I number from 0
+ upwards):
+ 
+ 0) at the lowest layer, there's a "block mode" which basically
+    supports bread/bwrite/bwritev by calling the equivalent iol_*
+    routines. It doesn't know about chunking, conversion, buffering and
+    the like. All it does is read/write with error handling.
+ 
+ 1) the next layer handles chunking. It knows about the current
+    chunking state and adds chunking information into the written
+    byte stream at appropriate places. It does not need to know about
+    buffering, or what the current (ebcdic?) conversion setting is.
+ 
+ 2) this layer handles conversion. I was thinking about a concept
+    where a generic character set conversion would be possible based on
+    Unicode-to-any translation tables. This would also deal with
+    multibyte character sets, because at this layer, it would
+    be easy to convert SBCS to MBCS.
+    Note that conversion *MUST* be positioned above the chunking layer
+    and below the buffering layer. The former guarantees that chunking
+    information is not converted twice (or not at all), and the latter
+    guarantees that ap_bgets() is looking at the converted data
+    (-- otherwise it would fail to find the '\n' which indicates end-
+    of-line).
+    Using (loadable?) translation tables based on unicode definitions
+    is a very similar approach to what libiconv offers you (see
+    http://clisp.cons.org/~haible/packages-libiconv.html -- though my
+    inspiration came from the russian apache, and I only heard about
+    libiconv recently). Every character set can be defined as a list
+    of <hex code> <unicode equiv> pairs, and translations between
+    several SBCS's can be collapsed into a single 256 char table.
+    Efficiently building them once only, and finding them fast is an
+    optimization task.
+ 
+ 3) This last layer adds buffering to the byte stream of the lower
+    layers. Because chunking and translation have already been dealt
+    with, it only needs to implement efficient buffering. Code
+    complexity is reduced to simple stdio-like buffering.
+ 
+ 
+ Creating a BUFF stream involves creation of the basic (layer 0) BUFF,
+ and then pushing zero or more filters (in the right order) on top of
+ it. Usually, this will always add the chunking layer, optionally add
+ the conversion layer, and usually add the buffering layer (look for
+ ap_bcreate() in the code: it almost always uses B_RD/B_WR).
+ 
+ Here's code from a conceptual prototype I wrote:
+     BUFF *buf = ap_bcreate(NULL, B_RDWR), *chunked, *buffered;
+     chunked   = ap_bpush_filter(buf,     chunked_filter, 0);
+     buffered  = ap_bpush_filter(chunked, buffered_filter, B_RDWR);
+     ap_bputs("Data for buffered ap_bputs\n", buffered);
+ 
+ 
+ Using a BUFF stream doesn't change: simply invoke the well known API
+ and call ap_bputs() or ap_bwrite() as you would today. Only, these
+ would be wrapper macros
+ 
+     #define ap_bputs(data, buf)             buf->bf_puts(data, buf)
+     #define ap_write(buf, data, max, lenp)  buf->bf_write(buf, data, max, lenp)
+ 
+ where a BUFF struct would hold function pointers and flags for the
+ various levels' input/output functions, in addition to today's BUFF
+ layout.
+ 
+ For performance improvement, the following can be added to taste:
+ 
+ * fewer buffering (zero copy where possible) by putting the buffers
+   for buffered reading/writing down as far as possible (for SBCS: from
+   layer 3 to layer 0). By doing this, the buffer can also hold a
+   chunking prefix (used by layer 1) in front of the buffering buffer
+   to reduce the number of vectors in a writev, or the number of copies
+   between buffers. Each layer could indicate whether it needs a
+   private buffer or not.
+ 
+ * intra-module calls can be hardcoded to call the appropriate lower
+   layer directly, instead of using the ap_bwrite() etc macros. That
+   means we don't use the function pointers all the time, but instead
+   call the lower levels directly. OTOH we have iol_* stuff which uses
+   function pointers anyway. We decided in 1.3 that we wanted to avoid
+   the C++ type stuff (esp. function pointers) for performance reasons.
+   But it would sure reduces the code complexity a lot.
+ 
+ The resulting layering would look like this:
+ 
+     | Caller: using ap_bputs() | or ap_bgets/apbwrite etc.
+     +--------------------------+
+     | Layer 3: Buffered I/O    | gets/puts/getchar functionality
+     +--------------------------+
+     | Layer 2: Code Conversion | (optional conversions)
+     +--------------------------+
+     | Layer 1: Chunking Layer  | Adding chunks on writes
+     +--------------------------+
+     | Layer 0: Binary Output   | bwrite/bwritev, error handling
+     +--------------------------+
+     | iol_* functionality      | basic i/o
+     +--------------------------+
+     | apr_* functionality      |
+     ....
+ 
+ -- 
+ <Martin.Kraemer@MchP.Siemens.De>             |    Fujitsu Siemens
+ Fon: +49-89-636-46021, FAX: +49-89-636-41143 | 81730  Munich,  Germany
+ 
+ 
+ ==============================
+ Date: Tue, 2 May 2000 09:09:28 -0700 (PDT)
+ From: dean gaudet <dgaudet-list-new-httpd@arctic.org>
+ To: new-httpd@apache.org
+ Subject: Re: BUFF, IOL, Chunking, and Unicode in 2.0 (long)
+ In-Reply-To: <20000502155129.A10548@pgtm0035.mch.sni.de>
+ Message-ID: <Pine.LNX.4.21.0005020847180.22518-100000@twinlark.arctic.org>
+ 
+ On Tue, 2 May 2000, Martin Kraemer wrote:
+ 
+ > * iol's sit below BUFF. Therefore, they don't have enough information
+ >   to know which part of the written byte stream is net client data,
+ >   and which part is protocol information (chunks, MIME headers for
+ >   multipart/*).
+ 
+ there's not much stopping you from writing an iol which takes a BUFF * in
+ its initialiser, and then bcreating a second BUFF, and bpushing your iol.
+ like:
+ 
+        /* this is in r->pool rather than r->connection->pool because
+         * we expect to create & destroy this inside request boundaries
+         * and if we stuck it in r->connection->pool the storage wouldn't
+         * be reclaimed earlier enough on pipelined connections.
+         *
+         * also, no need for buffering in new_buff because the translation
+         * layer can easily assume lower level BUFF is doing the buffering.
+         */
+        new_buff = ap_bcreate(r->pool, B_WR);
+        ap_bpush_iol(new_buff,
+                ap_utf8_to_ebcdic(r->pool, r->connection->client));
+        r->connection->client = new_buff;
+ 
+ main problem is that the new_buff only works for writing, and you
+ potentially need a separate conversion layer for reading from the
+ client.
+ 
+ shouldn't be too hard to split up r->connection->client into a read and
+ write half.
+ 
+ think of iol as the equivalent of the low level read/write, and BUFF
+ as the equivalent of FILE *.  there's a reason for both layers in
+ the interface.
+ 
+ > * iol's don't allow simplification of today's chunking code. It is
+ >   spread thruout buff.c and there's a very hairy balance between
+ >   efficiency and code correctness. Re-adding (EBCDIC/UTF) conversion,
+ >   possibly with sup[port for multi byte character sets (MBCS), would
+ >   make a code nightmare out of it. (buff.c in 1.3 was "almost" a
+ >   nightmare because we had onlu single byte translations.
+ 
+ as i've said before, i welcome anyone to do it otherwise without adding
+ network packets, without adding unnecessary byte copies, and without
+ making it even more complex.  until you've tried it, it's pretty easy
+ to just say "this is a mess".  once you've tried it i suspect you'll
+ discover why it is a mess.
+ 
+ that said, i'm still trying to prove to myself that the zero-copy
+ crud necessary to clean this up can be done in a less complex manner.
+ 
+ > * Putting conversion to a hierarchy level any higher than buff.c is no
+ >   solution either: for chunks, as well as for multipart headers and
+ >   buffering boundaries, we need character set translation. Pulling it
+ >   to a higher level means that a lot of redundant information has to
+ >   be passed down and up.
+ 
+ huh?  HTTP is in ASCII -- you don't need any conversion -- if a chunking
+ BUFF below a converting BUFF/iol is writing those things in ascii
+ it works.  no?  at least that's my understanding of the code in 1.3.
+ 
+ you wouldn't do the extra BUFF layer above until after you've written
+ the headers into the plain-text BUFF.
+ 
+ i would expect you'd:
+ 
+        write headers through plain text BUFF
+        push conversion BUFF
+        run method
+        pop conversion BUFF
+        pump multipart header
+        push conversion BUFF
+        ...
+        pop conversion BUFF
+ 
+ > In my understanding, we need a layered buff.c (which I number from 0
+ > upwards):
+ 
+ you've already got it :)
+ 
+ >     | Caller: using ap_bputs() | or ap_bgets/apbwrite etc.
+ >     +--------------------------+
+ >     | Layer 3: Buffered I/O    | gets/puts/getchar functionality
+ >     +--------------------------+
+ >     | Layer 2: Code Conversion | (optional conversions)
+ >     +--------------------------+
+ >     | Layer 1: Chunking Layer  | Adding chunks on writes
+ >     +--------------------------+
+ >     | Layer 0: Binary Output   | bwrite/bwritev, error handling
+ >     +--------------------------+
+ >     | iol_* functionality      | basic i/o
+ >     +--------------------------+
+ >     | apr_* functionality      |
+ 
+ there are two cases you need to consider:
+ 
+ chunking and a partial write occurs -- you need to keep track of how much
+ of the chunk header/trailer was written so that on the next loop around
+ (which happens in the application at the top) you continue where you
+ left off.
+ 
+ and more importantly at the moment, and easier to grasp -- consider what
+ happens when you've got a pipelined connection.  a dozen requests come
+ in from the client, and apache-1.3 will send back the minimal number
+ of packets.  2.0-current still needs fixing in this area (specifically
+ saferead needs to be implemented).
+ 
+ for example, suppose the client sends one packet:
+ 
+        GET /images/a.gif HTTP/1.1
+        Host: foo
+ 
+        GET /images/b.gif HTTP/1.1
+        Host: foo
+ 
+ suppose that a.gif and b.gif are small 200 byte files.
+ 
+ apache-1.3 sends back one response packet:
+ 
+        HTTP/1.1 OK
+        headers
+ 
+        a.gif body
+        HTTP/1.1 OK
+        headers
+ 
+        b.gif body
+ 
+ consider what happens with your proposal.  in between each of those
+ requests you remove the buffering -- which means you have to flush a
+ packet boundary.  so your proposal generates two network packets.
+ 
+ like i've said before on this topic -- if all unixes had TCP_CORK,
+ it'd be a breeze.  but only linux has TCP_CORK.
+ 
+ you pretty much require a layer of buffering right above the iol which
+ talks to the network.
+ 
+ and once you put that layer of buffering there, you might as well merge
+ chunking into it, because chunking needs buffering as well (specifically
+ for the async i/o case).
+ 
+ and then you either have to double-buffer, or you can only stack
+ non-buffered layers above it.  fortunately, character-set conversion
+ should be doable without any buffering.
+ 
+ *or* you implement a zero-copy library, and hope it all works out in
+ the end.
+ 
+ -dean
+ 


ossp-pkg/sio/BRAINSTORM/doc_greg_filters.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
--- -    Wed May  8 23:36:30 2024
***************
*** 0 ****
--- 1,102 ----
+ Date: Fri, 14 Apr 2000 13:46:50 -0700 (PDT)
+ From: Greg Stein <gstein@lyra.org>
+ To: new-httpd@apache.org
+ Subject: Re: I/O filtering in 2.0
+ In-Reply-To: <Pine.LNX.4.21.0004141156120.25805-100000@koj.rkbloom.net>
+ Message-ID: <Pine.LNX.4.10.10004141314030.13301-100000@nebula.lyra.org>
+ 
+ On Fri, 14 Apr 2000 rbb@covalent.net wrote:
+ > I am not calling this I/O Layering, because this is really output
+ > filtering.  The patch I am submitting allows modules to edit data after a
+ > handler has finished with it.  This is basically Greg's approach.
+ 
+ I'll detail my approach here, as your patch has some pieces, but it is
+ quite different.
+ 
+ All of this is obviously IMO...
+ 
+ 
+ *) we definitely want multiple output filters. each filter is recorded in
+    a linked list in the request_rec.
+ 
+ *) a filter has a name and is implemented by a module. this mapping is set
+    up similarly to handler maps in the 'module' structure.
+ 
+ *) output from normal modules is identical to today. they use ap_rputs,
+    ap_rwrite, etc. Filtering occurs under the covers.
+ 
+ *) Apache defines ap_lwrite(ap_layer *next_layer,
+                             const void *buf, size_t len,
+                             request_rec *r)
+    and possibly some similar ones for printf, puts, etc
+ 
+ *) struct ap_layer_s {
+       const char *layer_name;
+       layer_func_t *func;
+       struct ap_layer_s *next;
+    }
+ 
+    /* filters implement function with this type: */
+    typedef ap_status_t (*layer_func_t)(ap_layer *next_layer,
+                                        const void *buf, size_t len,
+                                        request_rec *r);
+    /* ### dunno about that return type */
+    /* looks remarkably similar to ap_lwrite(), eh? */
+ 
+ *) ap_status_t ap_lwrite(ap_layer *layer, const void *buf,
+                          size_t len, request_rec *r)
+    {
+        if (layer == NULL) {
+            ap_bwrite(r->connection->client, buf, len, &amt);
+            return OK;
+        }
+        return (*layer->func)(layer->next, buf, len, r);
+    }
+ 
+ *) a new Apache directive can detail the sequence of filters and install
+    them into the request_rec.
+ 
+ *) ap_rwrite() and friends calls ap_lwrite(r->first_layer, ...). this will
+    perform actual output filtering, or go off to the BUFF stuff.
+ 
+ *) a new hook is added: install_filters. it is called right before
+    invoke_handlers and is responsible for setting r->first_layer and/or
+    elements along the list.
+ 
+ *) a new, small module can implement a directive which responds to
+    install_filters and sets up a sequence of filters based on their names.
+    for example:
+       SetFilters PHP SSI
+ 
+ *) content handlers (e.g. during invoke_handler processing) have a new
+    function to call: ap_set_content_type(r, const char *type). when the
+    type is changed, such as during CGI processing, this function is called
+    and an opportunity (somehow? haven't thought on this part) is provided
+    for new output layers to be inserted.
+    [ this provides for a CGI output'ing application/x-httpd-php3 ]
+ 
+    ap_set_content_type() should probably know where it is during the
+    request processing so that it can be used any time. maybe it should be
+    allowed to set up layers at any time?
+ 
+ 
+ That's it. :-)
+ 
+ Helper functions to set up a pipe and a sub-thread would be handy. That
+ would allow some modules to keep their "read from an fd" approach, rather
+ than switching to a stateful parser approach. As Dean stated before,
+ output filtering is necessarily asynchronous: a sub thread or a state
+ machine thingy is required.
+ 
+ [ flipping things around, you could say that the initial content can be
+   generated asynchronously (where the first filter demands the next chunk
+   of output). this would be incredibly difficult for things like
+   mod_autoindex. at some point, somebody is pulling content and shoving it
+   down the BUFF. the above form is "everybody shoves content" ]
+ 
+ Cheers,
+ -g
+ 
+ -- 
+ Greg Stein, http://www.lyra.org/
+ 


ossp-pkg/sio/BRAINSTORM/doc_page_io.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
--- -    Wed May  8 23:36:30 2024
***************
*** 0 ****
--- 1,166 ----
+ 
+ From dgaudet@arctic.org Fri Feb 20 00:36:52 1998
+ Date: Fri, 20 Feb 1998 00:35:37 -0800 (PST)
+ From: Dean Gaudet <dgaudet@arctic.org>
+ To: new-httpd@apache.org
+ Subject: page-based i/o
+ X-Comment: Visit http://www.arctic.org/~dgaudet/legal for information regarding copyright and disclaimer.
+ Reply-To: new-httpd@apache.org
+ 
+ Ed asked me for more details on what I mean when I talk about "paged based
+ zero copy i/o". 
+ 
+ While writing mod_mmap_static I was thinking about the primitives that the
+ core requires of the filesystem.  What exactly is it that ties us into the
+ filesystem?  and how would we abstract it?  The metadata (last modified
+ time, file length) is actually pretty easy to abstract.  It's also easy to
+ define an "index" function so that MultiViews and such can be implemented. 
+ And with layered I/O we can hide the actual details of how you access
+ these "virtual" files. 
+ 
+ But therein lies an inefficiency.  If we had only bread() for reading
+ virtual files, then we would enforce at least one copy of the data. 
+ bread() supplies the place that the caller wants to see the data, and so
+ the bread() code has to copy it.  But there's very little reason that
+ bread() callers have to supply the buffer... bread() itself could supply
+ the buffer.  Call this new interface page_read().  It looks something like
+ this:
+ 
+     typedef struct {
+        const void *data;
+        size_t data_len; /* amt of data on page which is valid */
+        ... other stuff necessary for managing the page pool ...
+     } a_page_head;
+ 
+     /* returns NULL if an error or EOF occurs, on EOF errno will be
+      * set to 0
+      */
+     a_page_head *page_read(BUFF *fb);
+ 
+     /* queues entire page for writing, returns 0 on success, -1 on
+      * error
+      */
+     int page_write(BUFF *fb, a_page_head *);
+ 
+ It's very important that a_page_head structures point to the data page
+ rather than be part of the data page.  This way we can build a_page_head
+ structures which refer to parts of mmap()d memory.
+ 
+ This stuff is a little more tricky to do, but is a big win for performance.
+ With this integrated into our layered I/O it means that we can have
+ zero-copy performance while still getting the advantages of layering.
+ 
+ But note I'm glossing over a bunch of details... like the fact that we
+ have to decide if a_page_heads are shared data, and hence need reference
+ counting (i.e. I said "queues for writing" up there, which means some
+ bit of the a_page_head data has to be kept until its actually written).
+ Similarly for the page data.
+ 
+ There are other tricks in this area that we can take advantage of --
+ like interprocess communication on architectures that do page flipping.
+ On these boxes if you write() something that's page-aligned and page-sized
+ to a pipe or unix socket, and the other end read()s into a page-aligned
+ page-sized buffer then the kernel can get away without copying any data.
+ It just marks the two pages as shared copy-on-write, and only when
+ they're written to will the copy be made.  So to make this work, your
+ writer uses a ring of 2+ page-aligned/sized buffers so that it's not
+ writing on something the reader is still reading.
+ 
+ Dean
+ 
+ ----
+ 
+ For details on HPUX and avoiding extra data copies, see
+ <ftp://ftp.cup.hp.com/dist/networking/briefs/copyavoid.pdf>.
+ 
+ (note that if you get the postscript version instead, you have to 
+ manually edit it to remove the front page before any version of 
+ ghostscript that I have used will read it)
+ 
+ ----
+ 
+ I've been told by an engineer in Sun's TCP/IP group that zero-copy TCP
+ in Solaris 2.6 occurs when:
+ 
+     - you've got the right interface card (OC-12 ATM card I think)
+     - you use write()
+     - your write buffer is 16k aligned and a multiple of 16k in size
+ 
+ We currently get the 16k stuff for free by using mmap().  But sun's
+ current code isn't smart enough to deal with our initial writev()
+ of the headers and first part of the response.
+ 
+ ----
+ 
+ Systems that have a system call to efficiently send the contents of a 
+ descriptor across the network.  This is probably the single best way
+ to do static content on systems that support it.
+ 
+ HPUX: (10.30 and on)
+ 
+       ssize_t sendfile(int s, int fd, off_t offset, size_t nbytes,
+               const struct iovec *hdtrl, int flags);
+ 
+       (allows you to add headers and trailers in the form of iovec
+       structs)  Marc has a man page; ask if you want a copy.  Not included
+       due to copyright issues.  man page also available from 
+       http://docs.hp.com/ (in particular, 
+       http://docs.hp.com:80/dynaweb/hpux11/hpuxen1a/rvl3en1a/@Generic__BookTextView/59894;td=3 )
+ 
+ Windows NT:
+ 
+        BOOL TransmitFile(     SOCKET hSocket, 
+            HANDLE hFile, 
+            DWORD nNumberOfBytesToWrite, 
+            DWORD nNumberOfBytesPerSend, 
+            LPOVERLAPPED lpOverlapped, 
+            LPTRANSMIT_FILE_BUFFERS lpTransmitBuffers, 
+            DWORD dwFlags 
+           ); 
+ 
+        (does it start from the current position in the handle?  I would
+        hope so, or else it is pretty dumb.)
+ 
+        lpTransmitBuffers allows for headers and trailers.
+ 
+        Documentation at:
+ 
+        http://premium.microsoft.com/msdn/library/sdkdoc/wsapiref_3pwy.htm
+        http://premium.microsoft.com/msdn/library/conf/html/sa8ff.htm
+ 
+        Even less related to page based IO: just context switching:
+        AcceptEx does an accept(), and returns the start of the
+        input data.  see:
+ 
+        http://premium.microsoft.com/msdn/library/sdkdoc/pdnds/sock2/wsapiref_17jm.htm
+ 
+        What this means is you require one less syscall to do a
+        typical request, especially if you have a cache of handles
+        so you don't have to do an open or close.  Hmm.  Interesting
+        question: then, if TransmitFile starts from the current
+        position, you need a mutex around the seek and the
+        TransmitFile.  If not, you are just limited (eg. byte
+        ranges) in what you can use it for.
+ 
+        Also note that TransmitFile can specify TF_REUSE_SOCKET, so that
+        after use the same socket handle can be passed to AcceptEx.  
+        Obviously only good where we don't have a persistent connection
+        to worry about.
+ 
+ ----
+ 
+ Note that all this is shot to bloody hell by HTTP-NG's multiplexing.
+ If fragment sizes are big enough, it could still be worthwhile to
+ do copy avoidence.  It also causes performance issues because of
+ its credit system that limits how much you can write in a single
+ chunk.
+ 
+ Don't tell me that if HTTP-NG becomes popular we will seen vendors 
+ embedding SMUX (or whatever multiplexing is used) in the kernel to
+ get around this stuff.  There we go, Apache with a loadable kernel
+ module.  
+ 
+ ----
+ 
+ Larry McVoy's document for SGI regarding sendfile/TransmitFile:
+ ftp://ftp.bitmover.com/pub/splice.ps.gz


ossp-pkg/sio/BRAINSTORM/doc_stacked_io.txt -> 1.1

*** /dev/null    Wed May  8 23:33:00 2024
--- -    Wed May  8 23:36:30 2024
***************
*** 0 ****
--- 1,1312 ----
+ [djg: comments like this are from dean]
+ 
+ This past summer, Alexei and I wrote a spec for an I/O Filters API... 
+ this proposal addresses one part of that -- 'stacked' I/O with buff.c. 
+ 
+ We have a couple of options for stacked I/O: we can either use existing
+ code, such as sfio, or we can rewrite buff.c to do it.  We've gone over
+ the first possibility at length, though, and there were problems with each
+ implemenation which was mentioned (licensing and compatibility,
+ specifically); so far as I know, those remain issues. 
+ 
+ Btw -- sfio will be supported w/in this model... it just wouldn't be the
+ basis for the model's implementation. 
+ 
+      -- Ed Korthof        |  Web Server Engineer --
+      -- ed@organic.com    |  Organic Online, Inc --
+      -- (415) 278-5676    |  Fax: (415) 284-6891 --
+ 
+ ---------------------------------------------------------------------------
+ Stacked I/O With BUFFs
+        Sections:
+ 
+        1.) Overview
+        2.) The API
+                User-supplied structures
+                API functions
+        3.) Detailed Description
+                The bfilter structure
+                The bbottomfilter structure
+                The BUFF structure
+                Public functions in buff.c
+        4.) Efficiency Considerations
+                Buffering
+                Memory copies
+                Function chaining
+                writev
+        5.) Code in buff.c
+                Default Functions
+                Heuristics for writev
+                Writing
+                Reading
+                Flushing data
+                Closing stacks and filters
+                Flags and Options
+ 
+ *************************************************************************
+                Overview
+ 
+ The intention of this API is to make Apache's BUFF structure modular
+ while retaining high efficiency.  Basically, it involves rewriting
+ buff.c to provide 'stacked' I/O -- where the data passed through a
+ series of 'filters', which may modify it.
+ 
+ There are two parts to this, the core code for BUFF structures, and the
+ "filters" used to implement new behavior.  "filter" is used to refer to
+ both the sets of 5 functions, as shown in the bfilter structure in the
+ next section, and to BUFFs which are created using a specific bfliter.
+ These will also be occasionally refered to as "user-supplied", though
+ the Apache core will need to use these as well for basic functions.
+ 
+ The user-supplied functions should use only the public BUFF API, rather
+ than any internal details or functions.  One thing which may not be
+ clear is that in the core BUFF functions, the BUFF pointer passed in
+ refers to the BUFF on which the operation will happen.  OTOH, in the
+ user-supplied code, the BUFF passed in is the next buffer down the
+ chain, not the current one.
+ 
+ *************************************************************************
+                The API
+ 
+        User-supplied structures
+ 
+ First, the bfilter structure is used in all filters:
+     typedef struct {
+       int (*writev)(BUFF *, void *, struct iovect *, int);
+       int (*read)(BUFF *, void *, char *, int);
+       int (*write)(BUFF *, void *, const char *, int);
+       int (*flush)(BUFF *, void *, const char *, int, bfilter *);
+       int (*transmitfile)(BUFF *, void *, file_info_ptr *);
+       void (*close)(BUFF *, void *);
+     } bfilter;
+ 
+ bfilters are placed into a BUFF structure along with a
+ user-supplied void * pointer.
+ 
+ Second, the following structure is for use with a filter which can
+ sit at the bottom of the stack:
+ 
+     typedef struct {
+       void *(*bgetfileinfo)(BUFF *, void *);
+       void (*bpushfileinfo)(BUFF *, void *, void *);
+     } bbottomfilter;
+ 
+ 
+        BUFF API functions
+ 
+ The following functions are new BUFF API functions:
+ 
+ For filters:
+ 
+ BUFF * bcreatestack(pool *p, int flags, struct bfilter *,
+                     struct bbottomfilter *, void *);
+ BUFF * bpushfilter (BUFF *, struct bfilter *, void *);
+ BUFF * bpushbuffer (BUFF *, BUFF *);
+ BUFF * bpopfilter(BUFF *);
+ BUFF * bpopbuffer(BUFF *);
+ void bclosestack(BUFF *);
+ 
+ For BUFFs in general:
+ 
+ int btransmitfile(BUFF *, file_info_ptr *);
+ int bsetstackopts(BUFF *, int, const void *);
+ int bsetstackflags(BUFF *, int, int);
+ 
+ Note that a new flag is needed for bsetstackflags:
+ B_MAXBUFFERING
+ 
+ The current bcreate should become
+ 
+ BUFF * bcreatebuffer (pool *p, int flags, struct bfilter *, void *);
+ 
+ *************************************************************************
+                Detailed Explanation
+ 
+        bfilter structure
+ 
+ The void * pointer used in all these functions, as well as those in the
+ bbottomfilter structure and the filter API functions, is always the same
+ pointer w/in an individual BUFF.
+ 
+ The first function in a bfilter structure is 'writev'; this is only
+ needed for high efficiency writing, generally at the level of the system
+ interface.  In it's absence, multiple writes will be done w/ 'write'.
+ Note that defining 'writev' means you must define 'write'.
+ 
+ The second is 'write'; this is the generic writing function, taking a BUFF
+ * to which to write, a block of text, and the length of that block of
+ text.  The expected return is the number of characters (out of that block
+ of text) which were successfully processed (rather than the number of
+ characters actually written). 
+ 
+ The third is 'read'; this is the generic reading function, taking a BUFF *
+ from which to read data, and a void * buffer in which to put text, and the
+ number of characters to put in that buffer.  The expected return is the
+ number of characters placed in the buffer.
+ 
+ The fourth is 'flush'; this is intended to force the buffer to spit out
+ any data it may have been saving, as well as to clear any data the
+ BUFF code was storing.  If the third argument is non-null, then it
+ contains more text to be printed; that text need not be null terminated,
+ but the fourth argument contains the length of text to be processed.  The
+ expected return value should be the number of characters handled out
+ from the third argument (0 if there are none), or -1 on error.  Finally,
+ the fifth argument is a pointer to the bfilter struct containing this
+ function, so that it may use the write or writev functions in it.   Note
+ that general buffering is handled by BUFF's internal code, and module
+ writers should not store data for performance reasons.
+ 
+ The fifth is 'transmitfile', which takes as its arguments a buffer to
+ which to write (if non-null), the void * pointer containing configuration
+ (or other) information for this filter, and a system-dependent pointer
+ (the file_info_ptr structure will be defined on a per-system basis)
+ containing information required to print the 'file' in question.
+ This is intended to allow zero-copy TCP in Win32.
+ 
+ The sixth is 'close'; this is what is called when the connection is being
+ closed.  The 'close' should not be passed on to the next filter in the
+ stack.  Most filters will not need to use this, but if database handles
+ or some other object is created, this is the point at which to remove it.
+ Note that flush is called automatically before this.
+ 
+        bbottomfilter Structure
+ 
+ The first function, bgetfileinfo, is designed to allow Apache to get
+ information from a BUFF struct regarding the input and output sources.
+ This is currently used to get the input file number to select on a
+ socket to see if there's data waiting to be read.  The information
+ returned is platform specific; the void * pointer passed in holds
+ the void * pointer passed to all user-supplied functions.
+ 
+ The second function, bpushfileinfo, is used to push file information
+ onto a buffer, so that the buffer can be fully constructed and ready
+ to handle data as soon as possible after a client has connected.
+ The first void * pointer holds platform specific information (in
+ Unix, it would be a pair of file descriptors); the second holds the
+ void * pointer passed to all user-supplied functions.
+ 
+ [djg: I don't think I really agree with the distinction here between
+ the bottom and the other filters.  Take the select() example, it's
+ valid for any layer to define a fd that can be used for select...
+ in fact it's the topmost layer that should really get to make this
+ definition.  Or maybe I just have your top and bottom flipped.  In
+ any event I think this should be part of the filter structure and
+ not separate.]
+ 
+        The BUFF structure
+ 
+ A couple of changes are needed for this structure: remove fd and
+ fd_in; add a bfilter structure; add a pointer to a bbottomfilter;
+ add three pointers to the next BUFFs: one for the next BUFF in the
+ stack, one for the next BUFF which implements write, and one
+ for the next BUFF which implements read.
+ 
+ 
+        Public functions in buff.c
+ 
+ BUFF * bpushfilter (BUFF *, struct bfilter *, void *);
+ 
+ This function adds the filter functions from bfilter, stacking them on
+ top of the BUFF.  It returns the new top BUFF, or NULL on error.
+ 
+ BUFF * bpushbuffer (BUFF *, BUFF *);
+ 
+ This function places the second buffer on the top of the stack that
+ the first one is on.  It returns the new top BUFF, or NULL on error.
+ 
+ BUFF * bpopfilter(BUFF *);
+ BUFF * bpopbuffer(BUFF *);
+ 
+ Unattaches the top-most filter from the stack, and returns the new
+ top-level BUFF, or NULL on error or when there are no BUFFs
+ remaining.  The two are synonymous.
+ 
+ void bclosestack(BUFF *);
+ 
+ Closes the I/O stack, removing all the filters in it.
+ 
+ BUFF * bcreatestack(pool *p, int flags, struct bfilter *,
+                     struct bbottomfilter *, void *);
+ 
+ This creates an I/O stack.  It returns NULL on error.
+ 
+ BUFF * bcreatebuffer(pool *p, int flags, struct bfilter *, void *);
+ 
+ This creates a BUFF for later use with bpushbuffer.  The BUFF is
+ not set up to be used as an I/O stack, however.  It returns NULL
+ on error.
+ 
+ int bsetstackopts(BUFF *, int, const void *);
+ int bsetstackflags(BUFF *, int, int);
+ 
+ These functions, respectively, set options on all the BUFFs in a
+ stack.  The new flag, B_MAXBUFFERING is used to disable a feature
+ described in the next section, whereby only the first and last
+ BUFFs will buffer data.
+ 
+ *************************************************************************
+                Efficiency Considerations
+ 
+        Buffering
+ 
+ All input and output is buffered by the standard buffering code.
+ People writing code to use buff.c should not concern themselves with
+ buffering for efficiency, and should not buffer except when necessary.
+ 
+ The write function will typically be called with large blocks of text;
+ the read function will attempt to place the specified number of bytes
+ into the buffer.
+ 
+ Dean noted that there are possible problems w/ multiple buffers;
+ further, some applications must not be buffered.  This can be
+ partially dealt with by turning off buffering, or by flushing the
+ data when appropriate.
+ 
+ However, some potential problems arise anyway.  The simplest example
+ involves shrinking transformations; suppose that you have a set
+ of filters, A, B, and C, such that A outputs less text than it
+ recieves, as does B (say A strips comments, and B gzips the result).
+ Then after a write to A which fills the buffer, A writes to B.
+ However, A won't write enough to fill B's buffer, so a memory copy
+ will be needed.  This continues till B's buffer fills up, then
+ B will write to C's buffer -- with the same effect.
+ 
+ [djg: I don't think this is the issue I was really worried about --
+ in the case of shrinking transformations you are already doing 
+ non-trivial amounts of CPU activity with the data, and there's
+ no copying of data that you can eliminate anyway.  I do recognize
+ that there are non-CPU intensive filters -- such as DMA-capable
+ hardware crypto cards.  I don't think they're hard to support in
+ a zero-copy manner though.]
+ 
+ The maximum additional number of bytes which will be copied in this
+ scenario is on the order of nk, where n is the total number of bytes,
+ and k is the number of filters doing shrinking transformations.
+ 
+ There are several possible solutions to this issue.  The first
+ is to turn off buffering in all but the first filter and the
+ last filter.  This reduces the number of unnecessary byte copies
+ to at most one per byte, however it means that the functions in
+ the stack will get called more frequently; but it is the default
+ behavior, overridable by setting the B_MAXBUFFERING with
+ bsetstackflags.  Most filters won't involve a net shrinking
+ transformation, so even this will rarely be an issue; however,
+ if the filters do involve a net shrinking transformation, for
+ the sake of network-efficiency (sending reasonably sized blocks),
+ it may be more efficient anyway.
+ 
+ A second solution is more general use of writev for communication
+ between different buffers.  This complicates the programing work,
+ however.
+ 
+ 
+        Memory copies
+ 
+ Each write function is passed a pointer to constant text; if any changes
+ are being made to the text, it must be copied.  However, if no changes
+ are made to the text (or to some smaller part of it), then it may be
+ sent to the next filter without any additional copying.  This should
+ provide the minimal necessary memory copies.
+ 
+ [djg: Unfortunately this makes it hard to support page-flipping and
+ async i/o because you don't have any reference counts on the data.
+ But I go into a little detail that already in docs/page_io.]
+ 
+        Function chaining
+ 
+ In order to avoid unnecessary function chaining for reads and writes,
+ when a filter is pushed onto the stack, the buff.c code will determine
+ which is the next BUFF which contains a read or write function, and
+ reads and writes, respectively, will go directly to that BUFF.
+ 
+        writev
+ 
+ writev is a function for efficient writing to the system; in terms of
+ this API, however, it also works for dealing with multiple blocks of
+ text without doing unnecessary byte copies.  It is not required.
+ 
+ Currently, the system level writev is used in two contexts: for
+ chunking and when a block of text is writen which, combined with
+ the text already in the buffer, would make the buffer overflow.
+ 
+ writev would be implemented both by the default bottom level filter
+ and by the chunking filter for these operations.  In addition, writev
+ may, be used, as noted above, to pass multiple blocks of text w/o
+ copying them into a single buffer.  Note that if the next filter does
+ not implement writev, however, this will be equivalent to repeated
+ calls to write, which may or may not be more efficient.  Up to
+ IOV_MAX-2 blocks of text may be passed along in this manner.  Unlike
+ the system writev call, the writev in this API should be called only
+ once, with a array with iovec's and a count as to the number of
+ iovecs in it.
+ 
+ If a bfilter defines writev, writev will be called whether or not
+ NO_WRITEV is set; hence, it should deal with that case in a reasonable
+ manner.
+ 
+ [djg: We can't guarantee atomicity of writev() when we emulate it.
+ Probably not a problem, just an observation.]
+ 
+ *************************************************************************
+                Code in buff.c
+ 
+        Default Functions
+ 
+ The default actions are generally those currently performed by Apache,
+ save that they they'll only attempt to write to a buffer, and they'll
+ return an error if there are no more buffers.  That is, you must implement
+ read, write, and flush in the bottom-most filter.
+ 
+ Except for close(), the default code will simply pass the function call
+ on to the next filter in the stack.  Some samples follow.
+ 
+        Heuristics for writev
+ 
+ Currently, we call writev for chunking, and when we get a enough so that
+ the total overflows the buffer.  Since chunking is going to become a
+ filter, the chunking filter will use writev; in addition, bwrite will
+ trigger bwritev as shown (note that system specific information should
+ be kept at the filter level):
+ 
+ in bwrite:
+ 
+     if (fb->outcnt > 0 && nbyte + fb->outcnt >= fb->bufsiz) {
+         /* build iovec structs */
+         struct iovec vec[2];
+         vec[0].iov_base = (void *) fb->outbase;
+         vec[0].iov_len = fb->outcnt;
+         fb->outcnt = 0;
+         vec[1].iov_base = (void *)buff;
+         vec[1].iov_length = nbyte;
+         return bwritev (fb, vec, 2);
+     } else if (nbye >= fb->bufsiz) {
+         return write_with_errors(fb,buff,nbyte);
+     }
+ 
+ Note that the code above takes the place of large_write (as well
+ as taking code from it).
+ 
+ So, bwritev would look something like this (copying and pasting freely
+ from the current source for writev_it_all, which could be replaced):
+ 
+ -----
+ int bwritev (BUFF * fb, struct iovec * vec, int nvecs) {
+     if (!fb)
+         return -1; /* the bottom level filter implemented neither write nor
+                     * writev. */
+     if (fb->bfilter.bwritev) {
+         return bf->bfilter.writev(fb->next, vec, nvecs);
+     } else if (fb->bfilter.write) {
+         /* while it's nice an easy to build the vector and crud, it's painful
+          * to deal with partial writes (esp. w/ the vector)
+          */
+         int i = 0,rv;
+         while (i < nvecs) {
+             do {
+                 rv = fb->bfilter.write(fb, vec[i].iov_base, vec[i].iov_len);
+             } while (rv == -1 && (errno == EINTR || errno == EAGAIN)
+                      && !(fb->flags & B_EOUT));
+             if (rv == -1) {
+                 if (errno != EINTR && errno != EAGAIN) {
+                     doerror (fb, B_WR);
+                 }
+                 return -1;
+             }
+             fb->bytes_sent += rv;
+             /* recalculate vec to deal with partial writes */
+             while (rv > 0) {
+                 if (rv < vec[i].iov_len) {
+                     vec[i].iov_base = (char *)vec[i].iov_base + rv;
+                     vec[i].iov_len -= rv;
+                     rv = 0;
+                     if (vec[i].iov_len == 0) {
+                         ++i;
+                     }
+                 } else {
+                     rv -= vec[i].iov_len;
+                     ++i;
+                 }
+             }
+             if (fb->flags & B_EOUT)
+                 return -1;
+         }
+         /* if we got here, we wrote it all */
+         return 0;
+     } else {
+         return bwritev(fb->next,vec,nvecs);
+     }
+ }
+ -----
+ The default filter's writev function will pretty much like
+ writev_it_all.
+ 
+ 
+        Writing
+ 
+ The general case for writing data is significantly simpler with this
+ model.  Because special cases are not dealt with in the BUFF core,
+ a single internal interface to writing data is possible; I'm going
+ to assume it's reasonable to standardize on write_with_errors, but
+ some other function may be more appropriate.
+ 
+ In the revised bwrite (which I'll ommit for brievity), the following
+ must be done:
+        check for error conditions
+        check to see if any buffering is done; if not, send the data
+                directly to the write_with_errors function
+        check to see if we should use writev or write_with_errors
+                as above
+        copy the data to the buffer (we know it fits since we didn't
+                need writev or write_with_errors)
+ 
+ The other work the current bwrite is doing is
+        ifdef'ing around NO_WRITEV
+        numerous decisions regarding whether or not to send chunks
+ 
+ Generally, buff.c has a number of functions whose entire purpose is
+ to handle particular special cases wrt chunking, all of which could
+ be simplified with a chunking filter.
+ 
+ write_with_errors would not need to change; buff_write would.  Here
+ is a new version of it:
+ 
+ -----
+ /* the lowest level writing primitive */
+ static ap_inline int buff_write(BUFF *fb, const void *buf, int nbyte)
+ {
+     if (fb->bfilter.write)
+         return fb->bfilter.write(fb->next_writer,buff,nbyte);
+     else
+         return bwrite(fb->next_writer,buff,nbyte);
+ }
+ -----
+ 
+ If the btransmitfile function is called on a buffer which doesn't implement
+ it, the system will attempt to read data from the file identified
+ by the file_info_ptr structure and use other methods to write to it.
+ 
+        Reading
+ 
+ One of the basic reading functions in Apache 1.3b3 is buff_read;
+ here is how it would look within this spec:
+ 
+ -----
+ /* the lowest level reading primitive */
+ static ap_inline int buff_read(BUFF *fb, void *buf, int nbyte)
+ {
+     int rv;
+ 
+     if (!fb)
+         return -1; /* the bottom level filter is not set up properly */
+ 
+     if (fb->bfilter.read)
+         return fb->bfilter.read(fb->next_reader,buf,nbyte,fb->bfilter_info);
+     else
+         return bread(fb->next_reader,buff,nbyte);
+ }
+ -----
+ The code currently in buff_read would become part of the default
+ filter.
+ 
+ 
+        Flushing data
+ 
+ flush will get passed on down the stack automatically, with recursive
+ calls to bflush.  The user-supplied flush function will be called then,
+ and also before close is called.  The user-supplied flush should not
+ call flush on the next buffer.
+ 
+ [djg: Poorly written "expanding" filters can cause some nastiness
+ here.  In order to flush a layer you have to write out your current
+ buffer, and that may cause the layer below to overflow a buffer and
+ flush it.  If the filter is expanding then it may have to add more to
+ the buffer before flushing it to the layer below.  It's possible that
+ the layer below will end up having to flush twice.  It's a case where
+ writev-like capabilities are useful.]
+ 
+        Closing Stacks and Filters
+ 
+ When a filter is removed from the stack, flush will be called then close
+ will be called.  When the entire stack is being closed, this operation
+ will be done automatically on each filter within the stack; generally,
+ filters should not operate on other filters further down the stack,
+ except to pass data along when flush is called.
+ 
+        Flags and Options
+ 
+ Changes to flags and options using the current functions only affect
+ one buffer.  To affect all the buffers on down the chain, use
+ bsetstackopts or bsetstackflags.
+ 
+ bgetopt is currently only used to grab a count of the bytes sent;
+ it will continue to provide that functionality.  bgetflags is
+ used to provide information on whether or not the connection is
+ still open; it'll continue to provide that functionality as well.
+ 
+ The core BUFF operations will remain, though some operations which
+ are done via flags and options will be done by attaching appropriate
+ filters instead (eg. chunking).
+ 
+ [djg: I'd like to consider filesystem metadata as well -- we only need
+ a few bits of metadata to do HTTP: file size and last modified.  We
+ need an etag generation function, it is specific to the filters in
+ use.  You see, I'm envisioning a bottom layer which pulls data out of
+ a database rather than reading from a file.]
+ 
+ 
+ **************************************************************
+ **************************************************************
+ Date: Wed, 9 Sep 1998 18:55:40 -0700 (PDT)
+ From: Alexei Kosut <akosut@leland.stanford.edu>
+ To: new-httpd@apache.org
+ Subject: A Magic Cache example
+ Message-ID: <Pine.GSO.3.96.980909182642.29690A-100000@myth1.Stanford.EDU>
+ 
+ During the drive home, I came up with a good example of how I envision the
+ new module/cache/layer model thingy working. Comments please:
+ 
+ The middle end of the server is responsible for taking the request the
+ front end gives it and somehow telling the back end how to fulfill it. I
+ look at it like this: The request is a URI (Uniform Resource Identifier)
+ and a set of request dimensions (the request headers, the remote IP
+ address, the time of day, etc...). The middle end, via its configuration,
+ translates this into a request for content from a backing store module,
+ plus possibly some filter modules. Since the term "filename" is too
+ flat-file specific, let's call the parameter we pass to the backing store
+ a SRI (Specific Resource Identifier), in a format specific to that module.
+ 
+ Our example is similar to the one I was using earlier, with some
+ additions: The request is for a URI, say "/skzb/teckla.html". The response
+ is a lookup from a (slow) database. The URI maps to the mod_database SRI
+ of "BOOK:0-441-7997-9" (I made that format up). We want to take that
+ output and convert it from whatever charset it's in into Unicode. We then
+ have a PHP script that works on a Unicode document and does things based
+ on whether the browser is Netscape or not. Then we translate the document
+ to the best charset that matches the characters used and the client's
+ capabilities and send it.
+ 
+ So upon request for /skzb/teckla.html, the middle end translates the
+ request into the following "equation":
+ 
+         SRI: mod_database("BOOK:0-441-7997-9")
+     +   filter: mod_charset("Unicode")
+     +   filter: mod_php()
+     +   fllter: mod_charset("best_fit")
+  -------------------------------------------------
+         URI: /skzb/teckla.html
+ 
+ It then constructs a stack of IO (NSPR) filters like this:
+ 
+ mod_database -> cache-write -> mod_charset -> cache-write -> mod_php ->
+ cache_write -> mod_charset -> cache-write -> client
+ 
+ And sets it to running. Each of the cache filters is a write-through
+ filter that copies its data into the cache with a tag based on what
+ equation the middle end uses to get to it, plus the request dimensions it
+ uses (info it gets from the modules).
+ 
+ The database access is stored under "SRI: mod_database(BOOK:0-441-79977-9"
+ with no dimensions (because it's the same for all requests). The first
+ charset manipulation is stored under "SRI: mod_database(BOOK...) + filter:
+ mod_charset(Unicode)", again with no dimensions. The PHP output is stored
+ under "SRI: mod_database(BOOK...) + filter: mod_charset(Unicode) + filter:
+ mod_php()" with dimesions of (User-Agent). The final output is stored both
+ as "SRI: mod_database(BOOK...) + filter: mod_charset(Unicode) + filter:
+ mod_php() + filter: mod_charset(best_fit)" and "URI: /skzb/teckla.html"
+ (they're the same thing), both with dimensions of (User-Agent,
+ Accept-Charset).
+ 
+ So far so good. Now, when another request for /skzb/teckla.html comes in,
+ the cache is consulted to see how much we can use. First, the URI is
+ looked up. This can be done by a kernel or other streamlined part of the
+ server. So "URI: /skzb/teckla.html" is looked up, and one entry pops out
+ with dimensions of (User-Agent, Accept-Charset). The user-agent and
+ accept-charset of the request are compared against the ones of the stored
+ entiry(ies). If one matches, it can be sent directly.
+ 
+ If not, the server proceeds to look up "SRI: mod_database(BOOK...) +
+ filter: mod_charset(Unicode) + filter: mod_php()". If the request has a
+ different accept-charset, but the same user-agent, then this can be
+ reprocessed by mod_charset and used. Otherwise, the server proceeds back
+ to "SRI: mod_database(BOOK...) + filter: mod_charset(Unicode)", which will
+ match any request. There's probably some sort of cache invalidation
+ (expires, etc...) that happens eventually to result in a new database
+ lookup, but mostly, that very costly operation is avoided.
+ 
+ I think I've made it out to be a bit more complicated than it is, with the
+ long equation strings mixed in there. But the above reflects my
+ understanding of how the new Apache 2.0 system should work.
+ 
+ Note 1: The cache is smarter than I make it out here when it comes to
+ adding new entries. It should realize that, since the translation to
+ Unicode doesn't change or restrict the dimensions of the request, it
+ really is pointless to cache the original database lookup, since it will
+ always be translated in exactly the same manner. Knowing this, it will
+ only cache the Unicode version. 
+ 
+ Note 2: PHP probably doesn't work with Unicode. And there may not be a way
+ to identify a script as only acting on the User-Agent dimension. That's
+ not the point.
+ 
+ Note 3: Ten bonus points to anyone who's read this far, and is the first
+ person to answer today's trivia question: What does the skzb referred to
+ in the example URI stand for? There's enough information in this mail to
+ figure it out (with some help from the Net), even if you don't know
+ offhand (though if you do, I'd be happier). 
+ 
+ -- Alexei Kosut <akosut@stanford.edu> <http://www.stanford.edu/~akosut/>
+    Stanford University, Class of 2001 * Apache <http://www.apache.org> *
+ 
+ 
+ **************************************************************
+ Message-ID: <19980922224326.A16219@aisa.fi.muni.cz>
+ Date: Tue, 22 Sep 1998 22:43:26 +0200
+ From: Honza Pazdziora <adelton@informatics.muni.cz>
+ To: new-httpd@apache.org
+ Subject: Re: I/O Layering in next version of Apache.
+ References: <19980922111627.19784.qmail@hyperreal.org> <3607D53A.1FF6D93@algroup.co.uk> <13831.55021.929560.977122@zap.ml.org>
+ In-Reply-To: <13831.55021.929560.977122@zap.ml.org>; from Ben Hyde on Tue, Sep 22, 1998 at 01:04:12PM -0400
+ 
+ > >Does anyone have a starting point for layered I/O? I know we kicked it
+ 
+ Hello,
+ 
+ there has been a thread on modperl mailing list recently about
+ problems we have with the current architecture. Some of the points
+ were: what requerements will be put on modules to be new I/O
+ compliant. I believe it's the Apache::SSI vs. Apache::SSIChain
+ difference between 1.3.* and 2.*. The first fetches the file _and_
+ does the SSI, the second takes input from a different module that
+ either gets the HTML or runs the CGI or so, and processes its output.
+ Should all modules be capable of working on some other module's
+ output? Probably except those that actually go to disk or database for
+ the primary data.
+ 
+ Randal's point was that output of any module could be processed, so
+ that no module should make any assumption whether it's sending data
+ directly to the browser or to some other module. This can be used both
+ for caching, but it also one of the things to get the filtering
+ transparent.
+ 
+ Also, as Apache::GzipChain module shows, once you process the output,
+ you may need to modify the headers as well. I was hit by this when I
+ tried to convert between charsets, to send out those that the browsers
+ would understand. The Apache::Mason module shows that you can build
+ a page from pieces. Each of the pieces might have different
+ characteristics (charset, for example), so with each piece of code we
+ might need to have its own headers that describe it, or at least the
+ difference between the final (global) header-outs and its local.
+ 
+ Sorry for bringing so much Perl module names in, but modperl is
+ currently a way to get some layered I/O done in 1.3.*, so I only have
+ practical experiance with it.
+ 
+ Yours,
+ 
+ ------------------------------------------------------------------------
+  Honza Pazdziora | adelton@fi.muni.cz | http://www.fi.muni.cz/~adelton/
+                    I can take or leave it if I please
+ ------------------------------------------------------------------------
+ 
+ **************************************************************
+ Date: Wed, 23 Sep 1998 10:46:47 -0700 (PDT)
+ From: Dean Gaudet <dgaudet@arctic.org>
+ To: new-httpd@apache.org
+ Subject: Re: I/O Layering in next version of Apache.
+ In-Reply-To: <36092F2D.BCC4E5C1@algroup.co.uk>
+ Message-ID: <Pine.LNX.3.96dg4.980923103916.24223K-100000@twinlark.arctic.org>
+ 
+ On Wed, 23 Sep 1998, Ben Laurie wrote:
+ 
+ > Dean Gaudet wrote:
+ > > 
+ > > On Wed, 23 Sep 1998, Ben Laurie wrote:
+ > > 
+ > > > Is the simplest model that accomodates this actually just a stack
+ > > > (tree?) of webservers? Naturally, we wouldn't talk HTTP between the
+ > > > layers, but pass (header,content) pairs around (effectively).
+ > > > Interesting.
+ > > 
+ > > We could just talk "compiled" HTTP -- using a parsed representation of
+ > > everything essentially.
+ > 
+ > That's pretty much what I had in mind - but does it make sense? I have
+ > to admit, it makes a certain amount of sense to me, but I still have
+ > this nagging suspicion that there's a catch.
+ 
+ We talked about this during the developers meeting earlier this summer... 
+ while we were hiking, so I don't think there were any notes.
+ 
+ I think it'd be a useful exercise to specify a few example applications we
+ want to be able to support, and then consider methods of implementing
+ those applications.  Make the set as diverse and small as possible.  I'll
+ take the easiest one :)
+ 
+ - serve static content from arbitrary backing store (e.g. file, database) 
+ 
+ Once we flesh such a list out it may be easier to consider implementation
+ variations... 
+ 
+ I think it was Cliff who said it this way:  in a multiple layer setup he
+ wants to be able to partition the layers across servers in an arbtrary
+ manner.  For example, a proxy cache on one box which the world talks to,
+ and which backends to various other boxes for dynamic and static content.
+ Or maybe the static content is on the same server as the proxy. If this is
+ something we want to support then talking (a restricted form of) HTTP
+ between layers is interesting. 
+ 
+ Now we can all start worrying about performance ;) 
+ 
+ Dean
+ 
+ 
+ **************************************************************
+ Date: Wed, 23 Sep 1998 11:23:30 -0700 (PDT)
+ From: Alexei Kosut <akosut@leland.stanford.edu>
+ To: new-httpd@apache.org
+ Subject: Re: I/O Layering in next version of Apache.
+ In-Reply-To: <36092F2D.BCC4E5C1@algroup.co.uk>
+ Message-ID: <Pine.GSO.3.96.980923111613.17322C-100000@myth6.Stanford.EDU>
+ 
+ On Wed, 23 Sep 1998, Ben Laurie wrote:
+ 
+ > > We could just talk "compiled" HTTP -- using a parsed representation of
+ > > everything essentially.
+ > 
+ > That's pretty much what I had in mind - but does it make sense? I have
+ > to admit, it makes a certain amount of sense to me, but I still have
+ > this nagging suspicion that there's a catch.
+ 
+ One important thing to note is that we want this server to be able to
+ handle non-HTTP requests. So using HTTP as the internal language (as we do
+ now) is not the way to go. What we talked about in SF was using a basic
+ set of key/value pairs to represent the metadata of the response. Which
+ would of course bear an uncanny resemblance to HTTP-style MIME headers...
+ 
+ Certainly, and this is the point I think the originator of this thread
+ raised, each module layer (see the emails I sent a few weeks ago for more
+ details on how I see *that*) needs to provide both a content filter and a
+ metadata filter. Certainly a module that does encoding has to be able to
+ alter the headers to add a Content-Encoding, Transfer-Encoding, TE, or
+ what have you. Many module that does anything to the content will
+ want to add headers, and many others will need to alter the dimensions on
+ which the request is served, or what the parameters to those dimensions
+ are for the current request. The latter is absolutely vital for cacheing.
+ 
+ The problem, as I see it, is this: Often, I suspect it will be the case
+ that the module does not know what metadata it will be altering (and how)
+ until after it has processed the request. i.e., a PHP script may not
+ discover what dimensions it uses (as we discussed earlier) until after it
+ has parsed the entire script. But if the module is functioning as an
+ in-place filter, that can cause massive headaches if we need the metadata
+ in a complete form *before* we sent the entity, as we do for HTTP.
+ 
+ I'm not quite sure how to solve that problem. Anyone have any brilliant
+ ideas?
+ 
+ (Note that for internal caching, we don't actually need the dimension data
+ until after the request, because we can alter the state of the cache at
+ any time, but if we want to place nice with HTTP and send Vary: headers
+ and such, we do need that information. I guess we could send Vary:
+ footers...)
+ 
+ -- Alexei Kosut <akosut@stanford.edu> <http://www.stanford.edu/~akosut/>
+    Stanford University, Class of 2001 * Apache <http://www.apache.org> *
+ 
+ 
+ **************************************************************
+ Date: 23 Sep 1998 20:26:58 -0000
+ Message-ID: <19980923202658.25736.qmail@zap.ml.org>
+ From: Ben Hyde <bhyde@pobox.com>
+ To: new-httpd@apache.org
+ Subject: Stacking up Response Handling
+ In-Reply-To: <Pine.GSO.3.96.980923111613.17322C-100000@myth6.Stanford.EDU>
+ References: <36092F2D.BCC4E5C1@algroup.co.uk>
+        <Pine.GSO.3.96.980923111613.17322C-100000@myth6.Stanford.EDU>
+ 
+ Alexei Kosut writes:
+ >The problem, as I see it, is this: Often, I suspect it will be the case
+ >that the module does not know what metadata it will be altering (and how)
+ >until after it has processed the request. i.e., a PHP script may not
+ >discover what dimensions it uses (as we discussed earlier) until after it
+ >has parsed the entire script. But if the module is functioning as an
+ >in-place filter, that can cause massive headaches if we need the metadata
+ >in a complete form *before* we sent the entity, as we do for HTTP.
+ >
+ >I'm not quite sure how to solve that problem. Anyone have any brilliant
+ >ideas?
+ 
+ This is the same as building a layout engine that incremental layout
+ but simpler since I doubt we'd want to allow for reflow.
+ 
+ Sometimes you can send output right along, sometimes you have to wait.
+ I visualize the output as a tree/outline and as it is swept out a
+ stack holds the path to the leave.  Handlers for the individual nodes
+ wait or proceed depending on if they can.
+ 
+ It's pretty design with the pipeline consisting of this stack of
+ output transformers/generators.  Each pipeline stage accepts a stream
+ of output_chunks.  I think of these output_chunks as coming in plenty
+ of flavors, for example transmit_file, transmit_memory, etc.  Some
+ pipeline stages might handle very symbolic chunks.  For example
+ transmit_xml_tree might be handed to transform_xml_to_html stage in
+ the pipeline.
+ 
+ I'm assuming the core server would have only a few kinds of pipeline
+ nodes, generate_response, generate_content_from_url_via_file_system,
+ generate_via_classic_module_api.  Things like convert_char_set or
+ do_cool_transfer_encoding, could easily be loaded at runtime and
+ authored outside the core.  That would be nice.
+ 
+ For typical fast responses we wouldn't push much on this stack at
+ all.  It might go something like this: Push generate_response node, 
+ it selects an appropriate content generator by consulting the
+ module community and pushes that.  Often this is 
+ generate_content_from_url_via_file_system which in turn does
+ all that ugly mapping to a file name and then passes 
+ transmit_file down the pipeline and pops it's self off the stack.
+ generate_response once back on top again does the transmit and
+ pops off.
+ 
+ For rich complex output generation we might push all kinds of things
+ (charset converters, transfer encoders, XML -> HTML rewriters, cache
+ builders, old style apache module API simulators, what ever).
+ 
+ The intra-stack element protocol get's interesting around issues
+ like error handling, blocking, etc.  
+ 
+ I particularly like how this allows simulation of the old module API,
+ as well as the API of other servers, and experimenting with other
+ module API which cross process or machine boundaries.
+ 
+ In many ways this isn't that much different from what was proposed
+ a year ago.  
+ 
+  - ben
+ 
+ **************************************************************
+ From: Ben Hyde <bhyde@pobox.com>
+ Date: Wed, 23 Sep 1998 21:58:54 -0400 (EDT)
+ To: new-httpd@apache.org
+ Subject: Re: Core server caching
+ In-Reply-To: <Pine.GSO.3.96.980923142800.14009A-100000@elaine40.Stanford.EDU>
+ References: <19980923210119.25763.qmail@zap.ml.org>
+        <Pine.GSO.3.96.980923142800.14009A-100000@elaine40.Stanford.EDU>
+ Message-ID: <13833.39467.942203.885143@zap.ml.org>
+ 
+ Alexei Kosut writes:
+ >On 23 Sep 1998, Ben Hyde wrote:
+ >
+ >> The core problem of caching seems to me to get confused by the
+ >> complexity of designing a caching proxy.  If one ignores that then the
+ >> core problem of caching seems quite simple.
+ >
+ >Actually, for an HTTP server, they're the same problem, if you want to be
+ >able to cache any sort of dynamic request. And caching static requests is
+ >kind of silly (Dean's flow stuff notwithstanding, making copies of static
+ >files in either memory or on disk is silly, since the OS can do it better
+ >than we can).
+ 
+ I don't disagree with any of the things you said, so I guess I'm
+ failing to get across where in this structure the functions your
+ pointing out as necessary would reside as versus where the "chunk
+ cache" mechanism I'm yearning for would fit.
+ 
+ Well, that's not entirely true I do feel it's helpful to make this
+ point.
+ 
+ The HTTP spec's definition of proper caching is terribly constrained
+ by the poverty of information available to the proxy server.  He is
+ trapped in the middle between an opinionated content provider and an
+ opinionated content consumer.  It was written in an attempt to keep
+ people like AOL from making their opinions dominate either of those
+ other two.  Proper caching by a server that is right next to the
+ content generation can and ought to include both more or less
+ heuristics that are tunable by the opinions of the content provider
+ who presumably we are right next to.
+ 
+ Imagine the server that has a loop that goes like so:
+ 
+    loop
+      r<-swallow_incomming_request
+      h<-select_response_handler(r)
+      initialize_response_pipeline()
+      push_pipeline_element(h)
+      tend_pipeline_until_done()
+    end loop
+ 
+ In most of the web based applications I've seen the
+ select_response_handler step evolves into something that looks like an
+ AI expert system.  That said, what I'd like to see is in Apache2 is a
+ simple dispatch along with a way to plug-in more complex dispatching
+ mechanisms.  I'd very much like to avoid having that get confused with
+ the suite of response_handlers.
+ 
+ I ignored the complexity of when to you can safely select
+ a cached value because I think it's in the select_response_handler
+ step.  And possibly, I'll admit, not part of what I called the
+ "core server"
+ 
+ Clearly I'm a fool for using this term 'core server' since it
+ doesn't mean anything.  I wanted it to mean that loop above
+ and the most minimal implementations for the pipeline and
+ the select_response_handler one could imagine before starting
+ to pile on.  The server as shipped would have a lot more
+ stuff in it!
+ 
+ What I'm focused on is what has to be in that core versus
+ what has to be, but can be outside of it.
+ 
+ So. as i thought about the state of the pipeline just after
+ the call on initialize_response_pipeline I at first thought
+ it would have something much like the current buffer abstraction
+ in the pipeline.  Then i got to wondering if transfer encoding,
+ charset conversion, or caching ought to be in there.
+ 
+ I think there is an argument for putting some caching functionality
+ in there.  Possibly because that entire knot is what you'd move
+ into the OS if you could.  Possibly because this is the bit
+ that must fly.
+ 
+ Recall that I think the pipeline takes a stream of response
+ chunks with things like memory_chunk, transfer_file_chunk, etc.
+ in that stream.  The question is what flavors of chunks does
+ that bottom element in the pipeline take.  It's the chunks
+ that fly (and nothing more?).  So I got to thinking about
+ what does it mean to have a cached_chunk.
+ 
+ A cached_chunk needs only the small operation set along
+ the lines of what I mentioned.  A full caching scheme
+ can build on it.  As an added benefit the caching scheme
+ can be dumb, standard, extremely witty without effecting
+ this portion of the design.
+ 
+ A quick point about why I wanted the cache to handle things
+ smaller than entire responses.  This isn't central I guess.
+ 
+ I want a protocol with content generators that encourages
+ them to use dynamic programming tricks to quickly generate
+ portions of pages that are static over long periods.  Such
+ a scheme has worked well in systems we've built.
+ 
+  - ben hyde
+ 
+ **************************************************************
+ From: Ben Hyde <bhyde@pobox.com>
+ Date: Thu, 29 Oct 1998 23:16:37 -0500 (EST)
+ To: new-httpd@apache.org
+ Subject: Re: Core server caching
+ In-Reply-To: <Pine.LNX.3.96dg4.981029175439.3639X-100000@twinlark.arctic.org>
+ References: <Pine.WNT.4.05.9810292049480.-445955@helium.jetpen.com>
+        <Pine.LNX.3.96dg4.981029175439.3639X-100000@twinlark.arctic.org>
+ Message-ID: <13881.12903.661334.819447@zap.ml.org>
+ 
+ Dean Gaudet writes:
+ >On Thu, 29 Oct 1998, Rasmus Lerdorf wrote:
+ >
+ >> There are also weird and wacky things you would be able to do if you could
+ >> stack mod_php on top of mod_perl.
+ >
+ >You people scare me.
+ >
+ >Isn't that redundant though?
+ >
+ >Dean
+ 
+ Yes it's scary, but oddly erotic, when these behemoths with their
+ gigantic interpreters try to mate.
+ 
+ It's interesting syndrome, systems as soon as they get an interpreter
+ they tend to loose their bearings and grow into vast behemoths that
+ lumber about slowly crushing little problems with their vast mass.
+ Turing syndrome?
+ 
+ I've heard people say modules can help avoid this, but I've rarely
+ seen it.  Olde Unix kinda manages it remember being frightened by
+ awk.
+ 
+ Can we nudge alloc.c/buff.c toward a bit of connective glue that
+ continues to let individual modules evolve their own gigantism while
+ avoiding vile effects on the core performance of the server?  Stuff
+ like this:
+ 
+   memory chunk alignment for optimal I/O
+   memory hand off along the pipeline
+   memory hand off crossing pool boundaries
+   memory hand off in zero copy cases
+   transmit file
+   transmit cache elements
+   insert/remove cache elements
+   leverage unique hardware and instructions
+ 
+ That memcpy in ap_bread really bugs me.
+ 
+ I'd be rather have routines that let me handoff chunks.  Presumably
+ these would need to be able to move chunks across pool and buffer
+ boundaries.  But zero copy if I don't touch the content and never a
+ memcpy just to let my lex the input.
+ 
+ I've built systems like this with the buffers exposing a emacs
+ buffer style of abstraction, but with special kinds of marks
+ to denote what's released for sending, and what's been accepted
+ and lex'd on the input side.  It does create mean all your
+ lexical and printf stuff has to be able to smoothly slide
+ over chunk boundaries.
+ 
+  - ben
+ 
+ *************************************************************************
+ Date: Sun, 27 Dec 1998 13:08:22 -0800 (PST)
+ From: Ed Korthof <ed@bitmechanic.com>
+ To: new-httpd@apache.org
+ Subject: I/O filters & reference counts
+ Message-ID: <Pine.LNX.3.96.981224163237.10687E-100000@crankshaft>
+ 
+ Hi --
+ 
+ A while back, I indicated I'd propose a way to do reference counts w/ the
+ layered I/O I want to implement for 2.0 (assuming we don't use nspr)...
+ for single-threaded Apache, this seems unnecessary (assuming you don't use
+ shared memory in your filters to share data amoung the processes), but in
+ other situations it does have advantages.
+ 
+ Anyway, what I'd propose involves using a special syntax when you want to
+ use reference counts.  This allows Apache to continue using the
+ 'pool'-based memory system (it may not be perfect, but imo it's reasonably
+ good), without creating difficult when you wish to free memory.
+ 
+ If you're creating memory which you'll want to share amoung multiple
+ threads, you'll create it using a function more or less like: 
+ 
+     ap_palloc_share(pool *p, size_t size);
+ 
+ you get back a void * pointer for use as normal. When you want to give
+ someone else a reference to it, you do the following: 
+ 
+     ap_pshare_data(pool *p1, pool *p2, void * data);
+ 
+ where data is the return from above (and it must be the same).  Then both
+ pools have a reference to the data & to a counter; when each pool is
+ cleaned up, it will automatically decrement the counter, and free the data
+ if the counter is down to zero.
+ 
+ In addition, a pool can decrement the counter with the following:
+ 
+     ap_pshare_free(pool * p1, void * data);
+ 
+ after which the data may be freed.  There would also be a function,
+ 
+     ap_pshare_countrefs(pool * p1, void * data);
+ 
+ which would return the number of pools holding a ref to 'data', or 1 if
+ it's not a shared block.
+ 
+ Internally, the pool might either keep a list of the shared blocks, or a
+ balanced b-tree; if those are too slow, I'd look into passing back and
+ forth a (pointer to an) int, and simply use an array.  The filter
+ declaring the shared memory would need to keep track of such an int, but
+ no one else would. 
+ 
+ In the context of I/O filters, this would mean that each read function
+ returns a const char *, which should not be cast to a non-const char * (at
+ least, not without calling ap_pshare_countrefs()).  If a filter screwed
+ this up, you'd have a problem -- but that's more or less unavoidable with
+ sharing data amoung threads using reference counts. 
+ 
+ It might make sense to build a more general reference counting system; if
+ that's what people want, I'm also up for working on that.  But one of the
+ advantages the pool system has is its simplicity, some of which would be
+ lost.
+ 
+ Anyway, how does this sound?  Reasonable or absurd?
+ 
+ Thanks --
+ 
+ Ed
+                ----------------------------------------
+ History repeats itself, first as tragedy, second as farce. - Karl Marx
+ 
+ *************************************************************************
+ From: Ben Hyde <bhyde@pobox.com>
+ Date: Tue, 29 Dec 1998 11:50:01 -0500 (EST)
+ To: new-httpd@apache.org
+ Subject: Re: I/O filters & reference counts
+ In-Reply-To: <Pine.LNX.3.96.981227192210.10687H-100000@crankshaft>
+ References: <Pine.GSO.3.96.981227185303.8793B-100000@elaine21.Stanford.EDU>
+        <Pine.LNX.3.96.981227192210.10687H-100000@crankshaft>
+ Message-ID: <13960.60942.186393.799490@zap.ml.org>
+ 
+ 
+ There are two problems that reference counts address that we have,
+ but I still don't like them.
+ 
+ These two are: pipeline memory management, and response paste up.  A
+ good pipeline ought not _require_ memory proportional to the size of
+ the response but only proportional to the diameter of the pipe.
+ Response paste up is interesting because the library of clip art is
+ longer lived than the response or connection pool.  There is a lot to
+ be said for leveraging the configuration pool life cycle for this kind
+ of thing.
+ 
+ The pipeline design, and the handling of the memory it uses become
+ very entangled after a while - I can't think about one without the
+ other.  This is the right place to look at this problem.  I.e. this
+ is a problem to be lead by buff.c rework, not alloc.c rework.
+ 
+ Many pipeline operations require tight coupling to primitive
+ operations that happen to be efficient.  Neat instructions, memory
+ mapping, etc.  Extreme efficiency in this pipeline makes it desirable
+ that the chunks in the pipeline be large.  I like the phrase "chunks
+ and pumps" to summarize that there are two elements to design to get
+ modularity right here.
+ 
+ The pasteup problem - one yearns for a library of fragments (call it a
+ cache, clip art, or templates if you like) which then readers in that
+ library can assemble these into responses.  Some librarians like to
+ discard stale bits and they need a scheme to know that the readers
+ have all finished.  The library resides in a pool that lives longer
+ than a single response connection.  If the librarian can be convinced
+ that the server restart cycles are useful we get to a fall back to
+ there.
+ 
+ I can't smell yet where the paste up problem belong in the 2.0 design
+ problem.  (a) in the core, (b) in a module, (c) as a subpart of the
+ pipeline design, or (d) ostracized outside 2.0 to await a gift (XML?)
+ we then fold into Apache.  I could probably argue any one of these.  A
+ good coupling between this mechanism and the pipeline is good, limits
+ on the pipeline design space are very good.
+ 
+    - ben
+ 
+ 
+ *************************************************************************
+ Date: Mon, 4 Jan 1999 18:26:36 -0800 (PST)
+ From: Ed Korthof <ed@bitmechanic.com>
+ To: new-httpd@apache.org
+ Subject: Re: I/O filters & reference counts
+ In-Reply-To: <13960.60942.186393.799490@zap.ml.org>
+ Message-ID: <Pine.LNX.3.96.981231094653.486R-100000@crankshaft>
+ 
+ On Tue, 29 Dec 1998, Ben Hyde wrote:
+ 
+ > There are two problems that reference counts address that we have,
+ > but I still don't like them.
+ 
+ They certainly add some clutter.  But they offer a solution to the
+ problems listed below... and specifically to an issue which you brought up
+ a while back: avoiding a memcpy in each read layer which has a read
+ function other than the default one.  Sometimes a memcpy is required,
+ sometimes not; with "reference counts", you can go either way.
+ 
+ > These two are: pipeline memory management, and response paste up.  A
+ > good pipeline ought not _require_ memory proportional to the size of
+ > the response but only proportional to the diameter of the pipe.
+ > Response paste up is interesting because the library of clip art is
+ > longer lived than the response or connection pool.  There is a lot to
+ > be said for leveraging the configuration pool life cycle for this kind
+ > of thing.
+ 
+ I was indeed assuming that we would use pools which would last from one
+ restart (and a run through of the configuration functions) to the next.
+ 
+ So far as limiting the memory requirements of the pipeline -- this is
+ primarily a function of the module programming.  Because the pipeline will
+ generally live in a single thread (with the possible exception of the data
+ source, which could be another processes), the thread will only be
+ operating on a single filter at a time (unless you added custom code to
+ create a new thread to handle one part of the pipeline -- ugg).
+ 
+ For writing, the idea would be to print one or more blocks of text with
+ each call; wait for the write function to return; and then recycle the
+ buffers used.
+ 
+ Reading has no writev equivalent, so you only be able to do it one block
+ at a time, but this seems alright to me (reading data is actually a much
+ less complicated procedure in practice -- at least, with the applications
+ which I've seen).
+ 
+ Recycling read buffers (so as to limit the size of the memory pipeline)
+ is the hardest part, when we add in this 'reference count' scheme -- but
+ it can be done, if the modules recieving the data are polite and indicate
+ when they're done with the buffer.  Ie.:
+ 
+     module 1                   module 2
+ 1.) reads from module 2:
+        char * ap_bread(BUFF *, pool *, int);
+ 
+ 2.)                            returns a block of text w/ ref counts:
+                                        str= char* ap_pshare_alloc(size_t);
+                                        ...
+                                        return str;
+                                keeps a ref to str.
+                
+ 3.) handles the block of data
+     returned, and indicates it's
+     finished with:
+        void ap_pshare_free(char * block);
+     reads more data via
+        char * ap_bread(BUFF *, pool *, int);
+ 
+ 4.)                            tries to recycle the buffer used:
+                                        if (ap_pshare_count_refs(str)==1)
+                                                reuse str
+                                        else
+                                                str = ap_pshare_alloc(...)
+                                        ...
+                                        return str;
+ 
+ 5.) handles the block of data
+     returned...
+ ...
+ 
+ One disadvantage is that if module 1 doesn't release its hold on a memory
+ block it got from step 2 until step 5, then the memory block wouldn't be
+ reused -- you'd pay w/ a free & a malloc (or with a significant increase
+ in complexity -- I'd probably choose the free & malloc). And if the module
+ failed to release the memory (via ap_pshare_free), then the memory
+ requirements would be as large as the response (or request).
+ 
+ I believe this is only relevant for clients PUTting large files onto their
+ servers; but w/ files which are potentially many gigabytes, it is
+ important that filters handling reading do this correctly.  Of course,
+ that's currently the situation anyhow.
+ 
+ > The pipeline design, and the handling of the memory it uses become
+ > very entangled after a while - I can't think about one without the
+ > other.  This is the right place to look at this problem.  I.e. this
+ > is a problem to be lead by buff.c rework, not alloc.c rework.
+ 
+ Yeah, after thinking about it a little bit I realized that no (or very
+ little) alloc.c work would be needed to implement the system which I
+ described.  Basically, you'd have an Apache API function which does malloc
+ on its own, and other functions (also in the API) which register a cleanup
+ function (for the malloc'ed memory) in appropriate pools. 
+ 
+ IMO, the 'pipeline' is likely to be the easiest place to work with this,
+ at least in terms of getting the most efficient & clean design which we
+ can.
+ 
+ [snip good comments]
+ > I can't smell yet where the paste up problem belong in the 2.0 design
+ > problem.  (a) in the core, (b) in a module, (c) as a subpart of the
+ > pipeline design, or (d) ostracized outside 2.0 to await a gift (XML?)
+ > we then fold into Apache.  I could probably argue any one of these.  A
+ > good coupling between this mechanism and the pipeline is good, limits
+ > on the pipeline design space are very good.
+ 
+ An overdesigned pipeline system (or an overly large one) would definitely
+ not be helpful.  If it would be useful, I'm happy to work on this (even if
+ y'all aren't sure if you'd want to use it); if not, I'm sure I can find
+ things to do with my time. <g>
+ 
+ Anyway, I went to CPAN and got a copy of sfio... the latest version I
+ found is from Oct, 1997.  I'd guess that using it (assuming this is
+ possible) might give us slightly less efficency (simply because sfio
+ wasn't built specifically for Apache, and customizing it is a much more
+ involved processes), but possibly fewer bugs to work out & lots of
+ interesting features.
+ 
+ thanks --
+ 
+ Ed, slowly reading through the sfio source code
+ 


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+ Wishes -- use cases for layered IO
+ ==================================
+ 
+ [Feel free to add your own]
+ 
+ Dirk's original list:
+ ---------------------
+ 
+   This file is there so that I do not have to remind myself
+   about the reasons for Layered IO, apart from the obvious one.
+ 
+   0. To get away from a 1 to 1 mapping
+ 
+      i.e. a single URI can cause multiple backend requests, 
+      in arbitrary configurations, such as in paralel, tunnel/piped, 
+      or in some sort of funnel mode. Such multiple backend
+      requests, with fully layered IO can be treated exactly
+      like any URI request; and recursion is born :-)
+ 
+   1. To do on the fly charset conversion
+ 
+      Be, theoretically, be able to send out your content using
+      latin1, latin2 or any other charset; generated from static
+      _and_ dynamic content in other charsets (typically unicode
+      encoded as UTF7 or UTF8). Such conversion is prompted by
+      things like the user-agent string, a cookie, or other hints
+      about the capabilities of the OS, language preferences and
+      other (in)capabilities of the final receipient. 
+ 
+   2. To be able to do fancy templates
+ 
+      Have your application/cgi sending out an XML structure of
+      field/value pair-ed contents; which is substituted into a 
+      template by the web server; possibly based on information 
+      accessible/known to the webserver which you do not want to 
+      be known to the backend script. Ideally that template would
+      be just as easy to generate by a backend as well (see 0).
+ 
+   3. On the fly translation
+ 
+      And other general text and output mungling, such as translating
+      an english page in spanish whilst it goes through your Proxy,
+      or JPEG-ing a GIF generated by mod_perl+gd.
+ 
+   Dw.
+ 
+ 
+ Dean's canonical list of use cases
+ ----------------------------------
+ 
+ Date: Mon, 27 Mar 2000 17:37:25 -0800 (PST)
+ From: Dean Gaudet <dgaudet-list-new-httpd@arctic.org>
+ To: new-httpd@apache.org
+ Subject: canonical list of i/o layering use cases
+ Message-ID: <Pine.LNX.4.21.0003271648270.14812-100000@twinlark.arctic.org>
+ 
+ i really hope this helps this discussion move forward.
+ 
+ the following is the list of all applications i know of which have been
+ proposed to benefit from i/o layering.
+ 
+ - data sink abstractions:
+        - memory destination (for ipc; for caching; or even for abstracting
+                things such as strings, which can be treated as an i/o
+                object)
+        - pipe/socket destination
+        - portability variations on the above
+ 
+ - data source abstraction, such as:
+        - file source (includes proxy caching)
+        - memory source (includes most dynamic content generation)
+        - network source (TCP-to-TCP proxying)
+        - database source (which is probably, under the covers, something like
+                a memory source mapped from the db process on the same box,
+                or from a network source on another box)
+        - portability variations in the above sources
+ 
+ - filters:
+        - encryption
+        - translation (ebcdic, unicode)
+        - compression
+        - chunking
+        - MUX
+        - mod_include et al
+ 
+ and here are some of my thoughts on trying to further quantify filters:
+ 
+ a filter separates two layers and is both a sink and a source.  a
+ filter takes an input stream of bytes OOOO... and generates an
+ output stream of bytes which can be broken into blocks such
+ as:
+ 
+        OOO NNN O NNNNN ...
+ 
+        where O = an old or original byte copied from the input
+        and N = a new byte generated by the filter
+ 
+ for each filter we can calculate a quantity i'll call the copied-content
+ ratio, or CCR:
+ 
+        nbytes_old / nbytes_new
+ 
+ where:
+        nbytes_old = number of bytes in the output of the
+                filter which are copied from the input
+                (in zero-copy this would mean "copy by
+                reference counting an input buffer")
+        nbytes_new = number of bytes which are generated
+                by the filter which weren't present in the
+                input
+ 
+ examples:
+ 
+ CCR = infinity:  who cares -- straight through with no
+        transformation.  the filter shouldn't even be there.
+ 
+ CCR = 0: encryption, translation (ebcdic, unicode), compression.
+        these get zero benefit from zero-copy.
+ 
+ CCR > 0: chunking, MUX, mod_include
+ 
+ from the point of view of evaluating the benefit of zero-copy we only
+ care about filters with CCR > 0 -- because CCR = 0 cases degenerate into
+ a single-copy scheme anyhow.
+ 
+ it is worth noting that the large_write heuristic in BUFF fairly
+ clearly handles zero-copy at very little overhead for CCRs larger than
+ DEFAULT_BUFSIZE.
+ 
+ what needs further quantification is what the CCR of mod_include would
+ be.
+ 
+ for a particular zero-copy implementation we can find some threshold k
+ where filters with CCRs >= k are faster with the zero-copy implementation
+ and CCRs < k are slower... faster/slower as compared to a baseline
+ implementation such as the existing BUFF.
+ 
+ it's my opinion that when you consider the data sources listed above, and
+ the filters listed above that *in general* the existing BUFF heuristics
+ are faster than a complete zero-copy implementation.
+ 
+ you might ask how does this jive with published research such as the
+ IO-Lite stuff?  well, when it comes right down to it, the research in
+ the IO-Lite papers deal with very large CCRs and contrast them against
+ a naive buffering implementation such as stdio -- they don't consider
+ what a few heuristics such as apache's BUFF can do.
+ 
+ Dean
+ 
+ 
+ Jim's summary of a discussion
+ -----------------------------
+ 
+   OK, so the main points we wish to address are (in no particular order):
+ 
+      1. zero-copy
+      2. prevent modules/filters from having to glob the entire
+         data stream in order to start processing/filtering
+      3. the ability to layer and "multiplex" data and meta-data
+         in the stream
+      4. the ability to perform all HTTP processing at the
+         filter level (including proxy), even if not implemented in
+         this phase
+      5. Room for optimization and recursion
+ 
+   Jim Jagielski
+ 
+ 
+ Roy's ramblings
+ ---------------
+ 
+   Data flow networks are a very well-defined and understood software
+   architecture.  They have a single, very important constraint: no filter
+   is allowed to know anything about the nature of its upstream or downstream
+   neighbors beyond what is defined by the filter's own interface.
+   That constraint is what makes data flow networks highly configurable and
+   reusable.  Those are properties that we want from our filters.
+ 
+   ...
+ 
+   One of the goals of the filter concept was to fix the bird's nest of
+   interconnected side-effect conditions that allow buff to perform well
+   without losing the performance.  That's why there is so much trepidation
+   about anyone messin with 1.3.x buff.
+ 
+   ...
+ 
+   Content filtering is my least important goal.  Completely replacing HTTP
+   parsing with a filter is my primary goal, followed by a better proxy,
+   then internal memory caches, and finally zero-copy sendfile (in order of
+   importance, but in reverse order of likely implementation).  Content
+   filtering is something we get for free using the bucket brigade interface,
+   but we don't get anything for free if we start with an interface that only
+   supports content filtering.
+ 
+   ...
+ 
+   I don't think it is safe to implement filters in Apache without either
+   a smart allocation system or a strict limiting mechanism that prevents
+   filters from buffering more than 8KB [or user-definable amount] of memory
+   at a time (for the entire non-flushed stream).  It isn't possible to
+   create a robust server implementation using filters that allocate memory
+   from a pool (or the heap, or a stack, or whatever) without somehow
+   reclaiming and reusing the memory that gets written out to the network.
+   There is a certain level of "optimization" that must be present before
+   any filtering mechanism can be in Apache, and that means meeting the
+   requirement that the server not keel over and die the first time a user
+   requests a large filtered file.  XML tree manipulation is an example
+   where that can happen.
+ 
+   ...
+ 
+   Disabling content-length just because there are filters in the stream
+   is a blatant cop-out.  If you have to do that then the design is wrong.
+   At the very least the HTTP filter/buff should be capable of discovering
+   whether it knows the content length by examing whether it has the whole
+   response in buffer (or fd) before it sends out the headers.
+ 
+   ...
+ 
+   No layered-IO solution will work with the existing memory allocation
+   mechanisms of Apache.  The reason is simply that some filters can
+   incrementally process data and some filters cannot, and they often
+   won't know the answer until they have processed the data they are given.
+   This means the buffering mechanism needs some form of overflow mechanism
+   that diverts parts of the stream into a slower-but-larger buffer (file),
+   and the only clean way to do that is to have the memory allocator for the
+   stream also do paging to disk.  You can't do this within the request pool
+   because each layer may need to allocate more total memory than is available
+   on the machine, and you can't depend on some parts of the response being
+   written before later parts are generated because some filtering
+   decisions require knowledge of the end of the stream before they
+   can process the beginning.
+ 
+   ...
+ 
+   The purpose of the filtering mechanism is to provide a useful
+   and easy to understand means for extending the functionality of
+   independent modules (filters) by rearranging them in stacks
+   via a uniform interface.
+ 
+ 
+ Paul J. Reder's use cases for filters
+ -------------------------------------
+ 
+   1) Containing only text.
+   2) Containing 10 .gif or .jpg references (perhaps filtering
+      from one format to the other).
+   3) Containing an exec of a cgi that generates a text only file
+   4) Containing an exec of a cgi that generates an SSI of a text only file.
+   5) Containing an exec of a cgi that generates an SSI that execs a cgi
+      that generates a text only file (that swallows a fly, I don't know why).
+   6) Containing an SSI that execs a cgi that generates an SSI that
+      includes a text only file.
+      NOTE: Solutions must be able to handle *both* 5 and 6. Order
+            shouldn't matter.
+   7) Containing text that must be altered via a regular expression
+      filter to change all occurrences of "rederpj" to "misguided"
+   8) Containing text that must be altered via a regular expression
+      filter to change all occurrences of "rederpj" to "lost"
+   9) Containing perl or php that must be handed off for processing.
+   10) A page in ascii that needs to be converted to ebcdic, or from
+       one code page to another.
+   11) Use the babelfish translation filter to translate text on a
+       page from Spanish to Martian-Swahili.
+   12) Translate to Esperanto, compress, and encrypt the output from
+       a php program generated by a perl script called from a cgi exec
+       embedded in a file included by an SSI  :)
+ 


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+ <title>I/O Event Handling Under Linux</title>
+ 
+ <center>
+ <h1>I/O Event Handling Under Linux</h1>
+ <h2>Richard Gooch</h2>
+ <h4>28-JUN-1998</h4>
+ </center>
+ <hr>
+ 
+ <h4>Introduction</h4>
+ I/O Event handling is about how your Operating System allows you to
+ manage a large number of open files (file descriptors in UNIX/POSIX,
+ or FDs) in your application. You want the OS to notify you when FDs
+ become active (have data ready to be read or are ready for
+ writing). Ideally you want a mechanism that is scalable. This means a
+ large number of inactive FDs cost very little in memory and CPU time
+ to manage.
+ <p>
+ First I should start off by stating my goal: <b>to develop a thin
+ interface that makes best use of the facilities the OS provides,
+ scaling as much as possible. Where possible, use of standard POSIX
+ facilities are preferred</b>. A seconday goal is to provide a
+ convenient interface for applications. The reason for preferring
+ standard POSIX interfaces is that it introduces less conditional
+ blocks in the interface code.
+ 
+ <p>
+ <h4>The Traditional UNIX Way</h4>
+ Traditional Unix systems provide the <b>select(2)</b> and/or
+ <b>poll(2)</b> system calls. With both of these you pass an array of
+ FDs to the kernel, with an optional timeout. When there is activity,
+ or when the call times out, the system call will return. The
+ application must then scan the array to see which FDs are active. This
+ scheme works well with small numbers of FDs, and is simple to
+ use. Unfortunately, for thousands of FDs, this does not work so well.
+ 
+ <p>
+ The kernel has to scan your array of FDs and check which ones are
+ active. This takes approximately 3 microseconds (3 us) per FD on a
+ Pentium 100 running Linux 2.1.x. Now you might think that 3 us is
+ quite fast, but consider if you have an array of 1000 FDs. This is now
+ 3 milliseconds (3 ms), which is 30% of your timeslice (each timeslice
+ is 10 ms). If it happens that there is initially no activity and you
+ specified a timeout, the kernel will have to perform a <em>second</em>
+ scan after some activity occurs or the syscall times out. Ouch! If you
+ have an even bigger application (like a large http server), you can
+ easily have 10000 FDs. Scanning times will then take 30 ms, which is
+ three timeslices! This is just way too much.
+ 
+ <p>
+ You might say that 3 ms for 1000 FDs is not such a big deal: a user
+ will hardly notice that. The problem is that the entire array of FDs
+ is scanned <em>each time</em> you want to go back to your polling
+ loop. The way these applications work is that after checking for
+ activity on FDs, the application processes the activity (for example,
+ reading data from active FDs). When all the activity has been
+ processed, the application goes back to polling the OS for more FD
+ activity. In many cases, only a small number of FDs are active at any
+ one time (say during each timeslice), so it may only take a few
+ milliseconds to process all the activity. High performance http
+ servers can process hundreds or thousands of transactions per
+ second. A server that takes 2 ms to process each active FD can process
+ 500 transactions per second. If you add 3 ms for FD scanning in the
+ kernel, you now have 5 ms per transaction. That only gives 200
+ transactions per second, a massive drop in performance.
+ 
+ <p>
+ There is another problem, and that is that the application needs to
+ scan the "returned" FD array that the kernel has updated to see which
+ FDs are active. This is yet another scan of a large array. This isn't
+ as costly as the kernel scan, for reasons I'll get to later, but it is
+ still a finite cost.
+ 
+ <p>
+ <h4>New POSIX Interfaces</h4>
+ A fairly simple proposal is to use the POSIX.4 Asynchronous I/O (AIO)
+ interface (<b>aio_read()</b> and friends). Here we would call
+ <b>aio_read()</b> for each FD. This would then queue thousands of
+ asynchronous I/O requests. This model looks appealing, until we look
+ under the hood of some <b>aio_*()</b> implementations. The Linux glibc
+ implementation is a case in point: there is no kernel
+ support. Instead, the C library (glibc 2.1) launches a thread per FD
+ for which there are outstanding AIO requests (up to the maximum number
+ of configured threads).
+ In general, implementing this facility in the C library is reasonable,
+ as it avoids kernel bloat. However, if you use this facility to start
+ thousands of AIO requests, you may end up creating thousands of
+ threads. This is no good, since threads are costly. The "obvious"
+ solution is to implement AIO in the Linux kernel, then. Another
+ solution is to use userspace tricks to avoid the scalability problems
+ (see the description of migrating FDs below).  These solutions may be
+ fine if you only want to run under Linux, but is not much help if you
+ want to run under another OS which also implements AIO using threads
+ (and for which you don't have the source code so you can change the
+ implementation). The point here is that there appears to be no
+ guarantee that <b>aio_*()</b> implementations are scalable across
+ platforms which support it.
+ <p>
+ It is also worth noting that POSIX.4 Asynchronous I/O is not
+ necessarily available on all POSIX.4 compliant systems (facilities
+ defined by POSIX.4 are optional). So even if you were prepared to
+ limit your application to POSIX.4 systems, there is still no guarantee
+ that AIO is available. Many or most implementations <em>will</em> be
+ scalable, but we can't be sure all are scalable, so we need an
+ alternative.
+ <p>
+ I should also point out that I don't think that the POSIX.4 AIO
+ interface is particularly appropriate for a network server
+ application. AIO doesn't provide a callback interface, so it is harder
+ to build higher-layer network connection objects in your
+ application. So just writing a better (scalable) implementation of
+ AIO is not the ideal, either.
+ 
+ <p>
+ <h4>Readiness Event Queues and other OSes</h4>
+ Some other operating systems provide a mechanism called I/O completion
+ ports and some have event queues. These are a mechanism to tell the OS
+ that you want to be notified when there is activity on a FD. Usually,
+ when a FD becomes active (i.e. becomes ready for reading or writing) ,
+ the OS will send a message (a "readiness event") to a "port" (perhaps
+ another FD such as a pipe). This message contains the FD that has
+ become active. The one port can have many readiness events from many
+ FDs sent to it. The key difference here is that you do not need to
+ pass the OS a massive FD array each time you want to listen for
+ events: you only need to tell the OS once for each FD that you want to
+ receive readiness events for <em>that</em> FD. The kernel no longer
+ needs to scan a massive FD array each time through your polling loop,
+ and nor does the application. This is an appealing approach, and
+ scales very well.
+ 
+ <p>
+ Unfortunately, I/O readiness queues are not POSIX. They're not even
+ Unix. We could add them to Linux, but it would mean that applications
+ that relied on this mechanism would be unportable, Linux-only. Also,
+ it could involve significant additions to the kernel, which sets off
+ my bloat alarms. I would hope that it is possible to develop an
+ effective alternative that uses standard POSIX/UNIX functionality.
+ 
+ <p>
+ <h4>Optimising Existing UNIX Interfaces</h4>
+ There are improvements we can make for the massive FD scanning
+ problem. Firstly we can optimise the way the scanning is done inside
+ the kernel. Right now (2.1.106) the kernel has to call the
+ <b>poll()</b> method for each file structure. This is expensive. Back
+ in the 2.1.5x kernels, I coded a
+ <a
+ href="ftp://ftp.atnf.csiro.au/pub/people/rgooch/linux/kernel-patches/v2.1/fastpoll-readme">
+ better implementation</a>
+ for the kernel which sped things up almost 3 times. While this
+ requires modifications to drivers to take advantage of this, it has
+ the advantage of not changing the semantics we expect from UNIX. Note
+ one other interesting feature of this optimisation: it centralises
+ event notification, which in turn would make implementing I/O
+ readiness queues simpler. I'm not sure how closure of FDs before
+ readiness events are read should be handled. This could complicate
+ their implementation.
+ <p>
+ Doing this optimisation does not solve our problem, though. It only
+ pushes the problem away for a while.
+ 
+ <p>
+ <h4>Making Better Use of Existing UNIX Interfaces</h4>
+ Note that for my purposes, it is better to optimise the application so
+ that it works well on many OSes rather than optimising a single
+ OS. Creating new interfaces for Linux is a last resort. Also note that
+ this section assumes that an OS of interest does not have an existing
+ (preferably POSIX) mechanism that supports FD management in a scalable
+ way.
+ <p>
+ Another solution (which would also benefit from the kernel
+ optimisation discussed above) is for the application to divide the FD
+ array into a number of smaller FD arrays, say 10. You then create 10
+ threads, each of which has a polling loop using its smaller FD
+ array. So each FD array is now 100 entries long. While this doesn't
+ change the total number of FDs that must be scanned, it <em>does</em>
+ change <em>when</em> they have to be scanned. Since most FDs are
+ inactive, not all the threads will be woken up. Too see how this
+ works, consider the example where, at any time (say during a single
+ timeslice of 10 ms), only 5 FDs are active. Assuming these FDs are
+ randomly, uniformly distributed, at most 5 threads will need to be
+ woken up. These threads then process the activity and go back to the
+ start of their polling loops. Where we win is that only 5 threads had
+ to go back and call <b>select(2)</b> or <b>poll(2)</b>. Since they
+ each have 100 entry FD arrays, the kernel only has to scan 500
+ FDs. This has halved the amount of scanning required. The scanning
+ load has gone from 30% to 15% by this simple change. If you were to
+ instead use 100 threads, you would still only have at most 5 threads
+ woken up for activity, and hence the total number of FDs scanned this
+ timeslice would be 50. This takes down the scanning load to 0.15%,
+ which is negligible.
+ 
+ <p>
+ There is one thing to watch out for here: if you use <b>select(2)</b>
+ in your polling loop, be aware that the size of your FD array is equal
+ to the value of your largest FD. This is because <b>select(2)</b> uses
+ a bitmask for its FD array. This means one of your threads will want
+ to poll FDs 991 to 1000. Unfortunately, your FD array is still 1000
+ long. What's worse, the kernel still has to do a minimal scan for all
+ those 1000 FDs. The solution to this is to use <b>poll(2)</b> instead,
+ where you only have to pass as many FDs as you want to poll, and the
+ kernel scans only those.
+ <p>
+ This solution sounds ideal: just create lots and lots of threads. At
+ the extreme, you create one thread per FD. There is a problem here,
+ however, as each thread consumes system resources. So you need to
+ compromise between the number of threads and the FD scanning load.
+ Also, the more threads you have the more cache misses you induce, so
+ this is something to avoid as well. Fortunately in this case most
+ threads will be running nearly the same code at the same time, so
+ cache pollution should not be a significant problem.
+ <p>
+ A more advanced solution is to have dynamic migration of FDs depending
+ on whether they are mostly active or inactive. In the simplest case,
+ you only have two threads. One which polls mostly active FDs and the
+ other polls mostly inactive FDs. The thread for active FDs will be
+ woken up very frequently, but on the other hand will have only a small
+ number of FDs to scan. The other thread will have to scan a large
+ number of FDs, but it will only be woken up occasionally. For each FD
+ an activity counter is kept. When a FD on the mostly inactive list is
+ deemed to be fairly active, it is migrated to the mostly active
+ list. A reverse operation occurs for fairly inactive FDs on the mostly
+ active list.
+ <p>
+ I favour this solution, since it can be implemented solely in
+ userspace and is portable to other POSIX systems. I have an existing
+ <a href="http://www.atnf.csiro.au/karma/">software library</a> which
+ has (amongst other things) support for
+ <a href="http://www.atnf.csiro.au/karma/lib/dm.html">
+ managing events on FDs</a>. I plan on extending this library to use
+ the above technique. The library is distributed under the LGPL. Watch
+ this space for results.
+ <p>
+ My approach is to squeeze as much performance as we can out of the
+ existing POSIX/UNIX interface by optimising the kernel and doing
+ clever things in userspace. We can then evaluate how much of a
+ bottleneck polling is under Linux. If polling overheads (for very
+ large numbers of FDs) are kept to within a few percent, I firmly
+ believe there is no need for I/O readiness queues. If polling overheads
+ remain above 10%, then we may consider I/O readiness queues or other
+ extensions to Linux. However, it would be better to add kernel support
+ for scalable AIO rather than implement readiness queues, since AIO is
+ a POSIX standard whereas readiness queues are not.
+ 
+ <p>
+ <h4>Minor Additions to UNIX Interfaces</h4>
+ OK, now I'll get back to another point I raised earlier, and that is
+ the time taken for the application to scan a list of FDs for
+ activity. We would like to reduce this time as well, and we can
+ without much effort at all. Instead of using <b>poll(2)</b> we can
+ implement <b>poll2(2)</b>, a new syscall which is very much like
+ <b>poll(2)</b> but returns an array of <em>active</em> FDs. I
+ implemented this last year when I first started thinking about
+ optimising FD management under Linux.
+ <p>
+ So now the application only needs to search a very small array. This
+ new syscall is based on the principle of not duplicating work. The
+ kernel has just gone and scanned all these FDs for us, why not keep a
+ record of that work, rather than doing it again in the application?
+ Note that the current Linux polling implementation is so slow that
+ implementing <b>poll2(2)</b> will make little difference. However,
+ once the optimisations I've proposed are added, it <em>will</em> make
+ a difference (yes, I've done the benchmarks). Oh, and before you take
+ my comments on the Linux polling implementation too far, note that
+ I've benchmarked it against several other OSes, and Linux came out far
+ better in any case. My point is that we can still do a lot better.
+ 
+ <p>
+ You might ask, why implement <b>poll2(2)</b> if we have this clever
+ userspace solution that avoids many of the problems? Well, the point
+ is that it would speed up the application processing the inactive list
+ of FDs, and that is always a good thing. However, it may turn out that
+ the gain from <b>poll2(2)</b> is marginal. You could also argue that
+ since <b>poll2(2)</b> is non-POSIX, non-UNIX, then why bother with it
+ at all, and why not simply implement I/O readiness queues? Well, I
+ could say that <b>poll2(2)</b> is only a small departure from
+ UNIX whereas I/O readiness queues are more radical. However, this
+ isn't a very strong argument. I'm waiting to see the results of the
+ userspace solution before considering <b>poll2(2)</b>
+ further. Furthermore, it would be better to make the Linux
+ implementation of AIO scalable, since this is a standard POSIX
+ interface. So <b>poll2(2)</b> is probably dead. It does have one nice
+ feature, though: it would be easier for an application to change to
+ using <b>poll2(2)</b> than to change to using AIO.
+ 
+ <p>
+ Another possibility is to make a slight extension to the existing UNIX
+ asynchronous signal delivery mechanism. Currently, you can reqest the
+ OS to deliver a signal when a FD becomes ready for reading or
+ writing. Unfortunately, if you do this for multiple FDs your signal
+ handler doesn't know <em>which</em> FD is ready for activity. This is
+ because UNIX signals do not carry extra information with them. You
+ can't use a separate signal number for each FD, since UNIX has only a
+ few signal numbers. However, POSIX real-time signals can carry a word
+ of data to the signal handler. So we could extend Linux such that if
+ you request a POSIX RT signal to be delivered when an FD is ready for
+ I/O, the word of data is the FD number itself. Unfortunately,
+ depending on this behaviour would once again be Linux-specific.
+ However, such a system does look like an attractive way of providing
+ the foundations for a scalable AIO implementation.
+ 
+ <p>
+ <h4>Mixing and Matching</h4>
+ A good implementation of POSIX.4 AIO should be superior to my
+ migrating FD scheme, since AIO should require no polling
+ whatsoever. Therefore my interface code should be able to make use of
+ AIO if available. However, since an AIO implementation may in fact not
+ scale well, it's performance will have to be compared to the migrating
+ FD scheme to determine whether or not it should be utilised.
+ <p>
+ Similarly, for a system without POSIX.4 AIO but with readiness queues
+ it would make sense for the interface code to utilise this facility.
+ 
+ <p>
+ <h4>The Thundering Herd Problem</h4>
+ A note on the "thundering herd" problem: it's not really of much
+ interest in this discussion. The "problem" arises because people
+ attempt to increase concurrency of accepting new connections by having
+ multiple threads all blocking waiting on <b>select(2)</b>. Because the
+ kernel wakes up all threads, rather than one thread per new
+ connection, we have a "thundering herd" of freshly woken up
+ threads. These problems are best solved by treating the accepting of
+ incoming connections as just another case of I/O management, rather
+ than special-casing them.
+ 
+ <p>
+ <h4>Other Resources</h4>
+ Readers may find a recent <a
+ href="http://www.cs.rice.edu/~gaurav/my_papers/usenix98.ps">paper</a>
+ presented at USENIX98 of interest. The author also has a list of
+ <a href="http://www.cs.rice.edu/~gaurav/gaurav_research.html">
+ other research</a> on this topic. The paper essentially describes a
+ mechanism for improving the speed of <b>select(2)</b> by adding
+ internal state information to the kernel about FD activity.
+ 
+ <p>
+ <h4>Comments Please</h4>
+ I invite comments or additions to this document. My purpose is to
+ explain the various issues involved and serve as a primer for more
+ debate. I hope to avoid recurring debates on the linux-kernel list
+ which go over the same ground and either never contribute anything new
+ to the arguments, or take many messages before something new is
+ added. If you have a strong technical argument that I've missed, I'll
+ be happy to add it to this document.
+ 
+ <hr>
+ Original: 22-JUN-1998
+ <hr>
+ <a href="../../index.html">Back to my Home Page</a>
+ <hr>
+ <center>
+ <address>Richard Gooch (rgooch@atnf.csiro.au)</address>
+ </center>
+ </body>
+ </html>


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*** 0 ****
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+ 
+ stdio - 1990-1991 Steve Summit
+     reimplementated stdio, user-definable underlying I/O functions, improved
+     error handling, new routines for "string" I/O, and efficient unbuffered
+     I/O 
+ 
+ sfio - 1991-1998 David Korn and Kiem-Phong Vo, All rights reserved."
+     beherscht alle features, schwaches layering, portable, fast
+ 
+ sio - 1993 Panos Tsirigotis
+     kein socket support aber mmap
+ 
+ bstdio - 1993-1994 Chris Provenzano
+     threadsafe stdio based on the BSD stdio, uses pthreads
+ 
+ buff - 1995-1999 Robert S Thau, Apache Group
+     Apache Buffer and I/O library
+ 
+ substdio - Dan Berstein
+     - minimalistic stdio
+ 
+ bio - 199x-1999 Eric A. Young
+     BIO, sockets, memory, stacking
+ 
+ rt-aio - 1997 Ulrich Drepper
+     pthread basierte Async IO von glibc
+ 
+ 


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+ [(operation)-274 (w)9 (a)0 (k)10 (e)0 (s)-274 (one)-275 (w)10 (aiting)-275 (thread,)-275 (whereas)]TJ
+ /N95 1 Tf
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+ /N92 1 Tf
+ -33.6 -1.1667 TD
+ [(w)10 (a)0 (k)10 (e)0 (s)-230 (all)-229 (w)9 (aiting)-229 (threads)-230 (\(when)-229 (no)-230 (threads)-230 (are)-230 (w)10 (aiting,)-230 (both)-229 (operations)-230 (are)-230 (no-ops\).)-230 (When)-229 (a)-230 (w)10 (ait-)]TJ
+ T*
+ [(ing)-252 (thread)-253 (w)10 (a)0 (k)10 (e)0 (s)-252 (up,)-252 (it)-252 (reacquires)-252 (the)-252 (lock)-252 (the)-252 (same)-252 (number)-251 (of)-253 (times)-252 (it)-252 (held)-252 (it)-252 (prior)-252 (to)]TJ
+ /N95 1 Tf
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+ [(.)-253 (The)]TJ
+ -36.9425 -1.1667 TD
+ [(lock)-342 (reacquisition)-342 (puts)-342 (the)-342 (thread)-342 (into)-342 (competition)-342 (with)-342 (other)-342 (threads)-342 (attempting)-342 (to)-342 (acquire)-343 (the)]TJ
+ T*
+ [(lock,)-365 (including)-366 (both)-365 (other)-366 (a)15 (w)10 (ak)10 (ened)-365 (w)9 (aiters)-366 (and)-365 (threads)-366 (attempting)-365 (to)-365 (e)15 (x)15 (ecute)-366 (a)-366 (synchronized)]TJ
+ T*
+ [(method)-346 (or)-345 (statement.)-346 (Once)-346 (a)-345 (w)10 (aiting)-345 (thread)-346 (has)-345 (reacquired)-346 (the)-345 (lock,)-346 (the)]TJ
+ /N95 1 Tf
+ 30.0767 0 TD
+ (wait)Tj
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+ 2.7458 0 TD
+ [(operation)-345 (com-)]TJ
+ -32.8225 -1.1667 TD
+ [(pletes.)-239 (T)80 (o)-240 (simplify)-239 (matters,)-239 (in)-239 (this)-240 (paper)-239 (we)-240 (shall)-240 (not)-239 (discuss)-240 (interrupts)-239 (further)40 (,)-240 (e)16 (xcept)-240 (to)-239 (note)-240 (that)]TJ
+ T*
+ (in most of our implementation, an interrupt is handled similarly to a ti\
+ me-out.)Tj
+ /N91 1 Tf
+ 14 0 0 14 72 462.67 Tm
+ [(2.2  Bytecode-le)15 (v)10 (el synchr)18 (onization)]TJ
+ /N92 1 Tf
+ 12 0 0 12 72 438 Tm
+ [(Ha)20 (ving)-269 (described)-268 (synchronization)-267 (at)-268 (the)-268 (source)-268 (le)25 (v)15 (el,)-268 (we)-268 (no)25 (w)-268 (turn)-268 (to)-268 (the)-268 (bytecode)-268 (le)25 (v)15 (el.)-269 (In)-268 (byte-)]TJ
+ T*
+ [(code,)-693 (method)-692 (synchronization)-692 (is)-693 (performed)-692 (as)-693 (part)-692 (of)-693 (the)-693 (call/return)-692 (sequence:)-693 (if)-693 (the)]TJ
+ /N95 1 Tf
+ T*
+ (acc_synchronized)Tj
+ /N92 1 Tf
+ 9.8625 0 TD
+ [(attrib)20 (ute)-263 (is)-262 (set)-262 (on)-262 (a)-263 (method,)-262 (the)-262 (call)-263 (sequence)-262 (must)-262 (acquire)-263 (the)-262 (lock)-263 (\(one)]TJ
+ -9.8625 -1.1667 TD
+ [(more)-286 (time\))-286 (and)-286 (the)-286 (return)-285 (sequence)-286 (must)-286 (release)-286 (it)-286 (once.)-286 (Statement)-286 (synchronization)-286 (is)-285 (e)15 (xpressed)]TJ
+ T*
+ [(using)-368 (a)-368 (bytecode)-368 (pair)40 (,)]TJ
+ /N95 1 Tf
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+ (monitorenter)Tj
+ /N92 1 Tf
+ 7.5683 0 TD
+ (and)Tj
+ /N95 1 Tf
+ 1.8125 0 TD
+ (monitorexit)Tj
+ /N92 1 Tf
+ 6.6 0 TD
+ [(,)-368 (which)-368 (lock)-368 (and)-368 (unlock,)-369 (respec-)]TJ
+ -25.44 -1.1667 TD
+ [(ti)25 (v)15 (ely)65 (,)-322 (the)-323 (object)-322 (referenced)-322 (by)-322 (a)-323 (v)25 (alue)-322 (popped)-322 (from)-323 (the)-322 (JVM\325)55 (s)-322 (\322operand)-322 (stack.)70 (\323)-323 (Unfortunately)65 (,)]TJ
+ T*
+ [(while)-290 (the)-290 (bytecode)-290 (representation)-289 (of)-290 (synchronized)-289 (methods)-290 (is)-290 (inherently)-290 (well-nested,)-290 (there)-290 (is)-290 (no)]TJ
+ T*
+ [(such)-266 (guarantee)-266 (for)]TJ
+ /N95 1 Tf
+ 7.685 0 TD
+ (monitorenter)Tj
+ /N92 1 Tf
+ 7.4658 0 TD
+ (and)Tj
+ /N95 1 Tf
+ 1.7108 0 TD
+ (monitorexit)Tj
+ /N92 1 Tf
+ 6.6 0 TD
+ [(.)-266 (Nothing)-267 (pre)25 (v)15 (ents)-266 (bytecode)-266 (from)-267 (con-)]TJ
+ -23.4617 -1.1667 TD
+ [(taining)-290 (instruction)-290 (sequences)-291 (lik)10 (e)-290 (\322lock)]TJ
+ /N94 1 Tf
+ 16.2183 0 TD
+ (A)Tj
+ /N92 1 Tf
+ 0.6108 0 TD
+ [(,)-291 (lock)]TJ
+ /N94 1 Tf
+ 2.5533 0 TD
+ (B)Tj
+ /N92 1 Tf
+ 0.6108 0 TD
+ [(,)-290 (unlock)]TJ
+ /N94 1 Tf
+ 3.5525 0 TD
+ (A)Tj
+ /N92 1 Tf
+ 0.6117 0 TD
+ [(,)-290 (unlock)]TJ
+ /N94 1 Tf
+ 3.5525 0 TD
+ (B)Tj
+ /N92 1 Tf
+ 0.6108 0 TD
+ [(,)70 (\323)-291 (which)-290 (has)-290 (no)-291 (equi)25 (v)25 (alent)]TJ
+ -28.3208 -1.1667 TD
+ [(Ja)20 (v)25 (a)-264 (source)-264 (code.)-264 (The)-264 (loss)-264 (of)-264 (block)-264 (structure)-263 (at)-265 (the)-264 (bytecode)-264 (le)25 (v)15 (e)0 (l)-264 (mak)10 (es)-264 (it)-264 (dif)25 (\336cult)-264 (to)-264 (stack)-263 (allo-)]TJ
+ T*
+ [(cate)-366 (locking-related)-365 (data)-365 (structures.)-365 (Consequently)64 (,)-365 (t)0 (o)-365 (handle)-366 (non-LIFO)-365 (locking)-366 (and)-365 (unlocking,)]TJ
+ T*
+ (our implementation uses a free-list allocator \(see Section 6.1\).)Tj
+ 0 -1.75 TD
+ [(Concei)25 (v)25 (ably)65 (,)-319 (a)-319 (static)-320 (analysis)-319 (of)-319 (bytecode)-319 (could)-320 (conserv)25 (ati)25 (v)15 (ely)-319 (\322pair)-320 (up\323)]TJ
+ /N95 1 Tf
+ 30.0367 0 TD
+ (monitorenter)Tj
+ /N92 1 Tf
+ 7.5192 0 TD
+ (and)Tj
+ /N95 1 Tf
+ -37.5558 -1.1667 TD
+ (monitorexit)Tj
+ /N92 1 Tf
+ 7.0375 0 TD
+ [(instructions)-437 (in)-438 (most)-437 (cases,)-437 (allo)25 (wing)-437 (subsequent)-437 (e)15 (x)15 (ecution)-437 (to)-438 (assume)-438 (perfect)]TJ
+ -7.0375 -1.1667 TD
+ [(nesting.)-335 (W)80 (e)-335 (w)10 (ould)-335 (e)16 (xpect)-336 (this)-335 (analysis)-334 (to)-335 (succeed)-335 (most)-335 (of)-335 (the)-335 (time)-335 (on)-335 (bytecode)-335 (resulting)-335 (from)]TJ
+ T*
+ [(translation)-274 (of)-274 (Ja)20 (v)25 (a)-274 (source)-274 (code.)-274 (In)-274 (general,)-274 (ho)26 (we)24 (v)15 (e)0 (r)40 (,)-274 (the)-275 (problem)-274 (is)-275 (undecidable,)-274 (and)-274 (it)-274 (w)10 (ould)-274 (be)]TJ
+ T*
+ [(incorrect)-257 (to)-257 (reject)-258 (bytecode)-257 (for)-257 (which)-258 (the)-258 (analysis)-257 (f)10 (ails,)-257 (because)-258 (such)-257 (bytecode)-257 (is)-258 (still)-257 (le)15 (gal)-258 (i)0 (n)-258 (the)]TJ
+ T*
+ [(sense)-371 (that)-372 (it)-371 (passes)-371 (the)-371 (bytecode)-371 (v)15 (eri\336er)-371 ([18].)-371 (T)80 (o)-372 (further)-371 (complicate)-371 (the)-370 (picture,)-371 (JNI,)-371 (the)-371 (Ja)21 (v)25 (a)]TJ
+ T*
+ [(Nati)25 (v)15 (e)-390 (Interf)10 (ace,)-390 (grants)-390 (nati)25 (v)15 (e)-389 (code)-390 (access)-390 (to)-389 (synchronization)-390 (in)-390 (the)-390 (form)-390 (of)-389 (lock)-390 (and)-390 (unlock)]TJ
+ T*
+ [(operations,)-314 (so)-313 (e)26 (v)15 (en)-314 (if)-313 (all)-313 (bytecode)-314 (can)-314 (be)-313 (sho)25 (wn)-313 (to)-314 (be)-313 (structured,)-313 (a)-313 (f)10 (all-back)-314 (mechanism)-313 (w)10 (ould)]TJ
+ T*
+ [(still be needed for synchronization by nati)26 (v)15 (e)0 ( code.)]TJ
+ 0 -1.75 TD
+ [(Finally)65 (,)-361 (the)]TJ
+ /N95 1 Tf
+ 4.9633 0 TD
+ (wait)Tj
+ /N92 1 Tf
+ 2.7608 0 TD
+ (and)Tj
+ /N95 1 Tf
+ 1.8058 0 TD
+ (notify)Tj
+ /N92 1 Tf
+ 3.6 0 TD
+ ([)Tj
+ /N95 1 Tf
+ 0.3325 0 TD
+ (All)Tj
+ /N92 1 Tf
+ 1.8 0 TD
+ [(])-361 (operations)-361 (ha)20 (v)15 (e)-361 (no)-361 (direct)-361 (representation)-361 (at)-361 (the)-361 (bytecode)]TJ
+ -15.2625 -1.1667 TD
+ [(le)25 (v)15 (el,)-1103 (b)20 (u)0 (t)-1103 (instead)-1103 (are)-1103 (implemented)-1102 (as)-1103 (nati)24 (v)16 (e)-1103 (methods)-1102 (of)-1103 (the)-1103 (top-most)-1102 (class)]TJ
+ T*
+ (\()Tj
+ /N95 1 Tf
+ 0.3333 0 TD
+ (java.lang.Object)Tj
+ /N92 1 Tf
+ 9.6 0 TD
+ (\).)Tj
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
+ %%EndPage
+ %%Page: 7 7
+ %%BeginPageSetup
+ userdict /pgsave save put
+ PDFVars begin PDF begin PDFVars/InitAll get exec
+ %%EndPageSetup
+ 0 0 612 792 RC
+ 1 g
+ /N93 /ExtGState findRes gs
+ 1 i
+ 0 0 612 792 re
+ f 
+ BT
+ /N92 1 Tf
+ 12 0 0 12 303 34.17 Tm
+ 0 g
+ 0 Tc
+ 0 Tw
+ (4)Tj
+ /N91 1 Tf
+ 16 0 0 16 72 709.33 Tm
+ [(3  Related w)10 (ork)]TJ
+ /N92 1 Tf
+ 12 0 0 12 72 686 Tm
+ [(There)-309 (is)-308 (a)-309 (lar)18 (ge)-308 (general)-309 (literature)-308 (on)-309 (synchronization)-307 (primiti)25 (v)15 (e)0 (s)-309 (and)-308 (their)-309 (implementation.)-308 (Dijk-)]TJ
+ 0 -1.1667 TD
+ [(stra)-278 ([9])-277 (and)-278 (Lamport)-277 ([16])-278 (present)-279 (subtle)-278 (algorithms)-278 (that)-278 (achie)25 (v)15 (e)-278 (mutual)-278 (e)15 (xclusion)-277 (assuming)-278 (only)]TJ
+ T*
+ [(that)-289 (indi)25 (vidual)-290 (reads)-289 (and)-288 (writes)-289 (are)-290 (atomic.)-289 (F)15 (ortunately)65 (,)-290 (modern)-289 (architectures)-289 (pro)16 (vide)-290 (composite)]TJ
+ T*
+ [(instructions)-287 (such)-287 (as)-286 (compare-and-sw)10 (ap)-287 (that)-287 (read)-286 (and)-287 (write)-287 (a)-287 (memory)-287 (location)-286 (in)-287 (a)-288 (single)-287 (atomic)]TJ
+ T*
+ [(step,)-241 (greatly)-241 (simplifying)-241 (the)-241 (mutual)-241 (e)15 (xclusion)-242 (problem)-241 (and)-241 (eliminating)-241 (the)-241 (need)-241 (for)-241 (such)-242 (subtlety)65 (.)]TJ
+ T*
+ [(W)80 (e)-276 (shall)-277 (refer)-277 (to)-276 (the)-276 (composite)-277 (atomic)-276 (instructions)-276 (simply)-277 (as)-276 (\322atomic)-276 (instructions.)70 (\323)-277 (W)81 (eakly)-277 (con-)]TJ
+ T*
+ [(sistent)-245 (memory)-243 (models,)-244 (which)-245 (allo)25 (w)-244 (dif)24 (ferent)-244 (processors)-245 (to)-244 (observ)15 (e)-244 (memory)-244 (operations)-244 (as)-244 (occur-)]TJ
+ T*
+ [(ring)-501 (in)-500 (dif)25 (ferent)-500 (orders,)-500 (may)-500 (require)-500 (the)-500 (use)-500 (of)-500 (memory)-500 (barrier)-500 (instructions)-500 (to)-500 (reintroduce)]TJ
+ T*
+ [(consistenc)15 (y)65 (,)0 ( whether using indi)25 (vidual reads and writes or atomic instructions.)]TJ
+ 0 -1.75 TD
+ [(In)-247 (its)-247 (broad)-246 (structure,)-247 (our)-247 (meta-lock)-246 (resembles)-247 (the)-247 (MCS-lock)-246 (of)-247 (Mellor)20 (-Crumme)15 (y)-247 (and)-247 (Scott)-246 ([20].)]TJ
+ 0 -1.1667 TD
+ [(The)-261 (MCS-lock)-261 (uses)-261 (an)-261 (atomic)-261 (sw)10 (ap)-261 (for)-261 (lock)-261 (acquisition)-261 (and)-261 (an)-261 (atomic)-261 (compare-and-sw)10 (ap)-261 (\()]TJ
+ /N95 1 Tf
+ 36.8667 0 TD
+ (CAS)Tj
+ /N92 1 Tf
+ 1.8 0 TD
+ (\))Tj
+ -38.6667 -1.1667 TD
+ [(for)-251 (lock)-250 (release)-251 (in)-250 (much)-250 (the)-250 (same)-250 (w)10 (a)0 (y)-250 (a)0 (s)-250 (does)-250 (our)-249 (meta-lock)-251 (algorithm.)-250 (The)-250 (MCS-lock)-250 (has)-250 (man)15 (y)]TJ
+ T*
+ [(of)-377 (the)-377 (same)-377 (properties)-377 (as)-377 (our)-377 (meta-lock,)-377 (including)-377 (starv)25 (ation)-377 (freedom)-377 (and)-378 (FIFO)-377 (access)-377 (to)-378 (the)]TJ
+ T*
+ [(lock.)-245 (Ho)25 (we)25 (v)15 (e)0 (r)40 (,)-244 (the)-245 (details)-245 (are)-244 (quite)-245 (dif)25 (ferent)-245 (and,)-244 (in)-244 (particular)40 (,)-244 (contention)-244 (results)-244 (in)-245 (b)20 (usy-w)11 (aiting.)]TJ
+ T*
+ [(Also,)-285 (space-ef)25 (\336cienc)15 (y)-285 (i)0 (s)-285 (not)-284 (as)-285 (e)15 (xtreme)-285 (a)-285 (concern)-285 (in)-284 (the)-285 (conte)15 (xt)-285 (of)-284 (their)-285 (w)10 (ork.)-285 (Magnusson)]TJ
+ /N94 1 Tf
+ 36.965 0 TD
+ [(et)-285 (al.)]TJ
+ /N92 1 Tf
+ -36.965 -1.1667 TD
+ [([19])-324 (surv)15 (e)15 (y)-324 (locking)-323 (schemes)-323 (related)-324 (to)-324 (MCS-locks,)-324 (and)-324 (describe)-324 (tw)10 (o)-323 (n)0 (e)25 (w)-324 (locking)-324 (schemes)-323 (that)]TJ
+ T*
+ [(of)25 (fer dif)25 (ferent performance trade-of)26 (fs.)]TJ
+ 0 -1.75 TD
+ [(Brinch)-249 (Hansen)-248 ([11])-248 (and)-248 (Hoare)-249 ([12])-249 (coined)-248 (the)-249 (term)]TJ
+ /N94 1 Tf
+ 20.8983 0 TD
+ (monitor)Tj
+ /N92 1 Tf
+ 3.1267 0 TD
+ [(,)-249 (and)-248 (pro)16 (vided)-249 (the)-248 (nomenclature)-248 (used)]TJ
+ -24.025 -1.1667 TD
+ [(by)-226 (the)-226 (Ja)21 (v)25 (a)-226 (language.)-226 (There)-225 (are)-226 (se)26 (v)15 (eral)-226 (w)9 (ays,)-225 (ho)25 (we)24 (v)15 (e)0 (r)40 (,)-226 (in)-226 (which)-226 (the)-226 (monitors)-225 (in)-226 (the)-225 (Ja)20 (v)25 (a)-226 (language)]TJ
+ T*
+ [(dif)25 (fer)-355 (from)-354 (the)-354 (original:)-354 (an)15 (y)-355 (object)-354 (may)-354 (be)-355 (used)-354 (as)-354 (a)-355 (monitor)41 (,)-354 (monitors)-355 (may)-354 (be)-355 (entered)-354 (recur-)]TJ
+ T*
+ [(si)25 (v)15 (ely)65 (,)-382 (and)-383 (monitors)-383 (pro)15 (vide)-382 (a)-384 (single)-383 (implicit,)-383 (rather)-382 (than)-383 (possibly)-382 (se)25 (v)15 (eral)-383 (e)15 (xplicit,)-383 (\322condition)]TJ
+ T*
+ [(v)25 (ariables.)70 (\323)-379 (Birrell)-380 (gi)26 (v)15 (e)0 (s)-379 (a)0 (n)-380 (e)16 (xcellent)-380 (tutorial)-379 (on)-380 (programming)-379 (with)-379 (\322standard\323)-379 (synchronization)]TJ
+ T*
+ [(primiti)25 (v)15 (e)0 (s)-235 ([5].)-236 (As)-236 (we)-236 (ha)20 (v)15 (e)-236 (discussed,)-235 (the)-236 (synchronization)-235 (primiti)25 (v)15 (e)0 (s)-236 (o)0 (f)-235 (the)-236 (Ja)21 (v)25 (a)-236 (platform)-236 (are)-236 (dif)25 (\336-)]TJ
+ T*
+ [(cult)-262 (to)-262 (implement)-262 (in)-262 (a)-262 (manner)-262 (that)-262 (is)-261 (both)-262 (time-)-262 (and)-262 (space-ef)25 (\336cient.)-262 (Scalability)-262 (to)-262 (multiprocessor)]TJ
+ T*
+ [(systems)-444 (is)-444 (another)-444 (important)-443 (concern.)-444 (W)80 (e)-444 (shall)-444 (no)25 (w)-444 (discuss)-443 (some)-444 (pre)25 (vious)-444 (implementations)]TJ
+ T*
+ [(focusing on the approach the)15 (y tak)10 (e to trading of)25 (f these concerns.)]TJ
+ 0 -1.75 TD
+ [(The)-342 (original)-343 (JDK\252)-342 (implementation)-342 (of)-343 (the)-343 (Ja)21 (v)25 (a)-343 (virtual)-343 (machine)-342 ([18])-343 (pro)16 (vides)-343 (a)-343 (space-ef)25 (\336cient)]TJ
+ 0 -1.1667 TD
+ [(monitor)-374 (implementation,)-373 (b)20 (u)0 (t)-374 (one)-374 (that)-374 (is)-375 (not)-374 (particularly)-374 (time-ef)25 (\336cient)-374 (or)-374 (scalable.)-374 (This)-374 (design)]TJ
+ T*
+ [(requires)-260 (that)-260 (each)-260 (object)-260 (has)-260 (a)-260 (unique)-260 (identi\336er)-260 (v)25 (alid)-260 (o)14 (v)16 (er)-260 (its)-260 (lifetime.)-260 (The)-260 (actual)-260 (implementation)]TJ
+ T*
+ [(uses)-336 (an)]TJ
+ /N94 1 Tf
+ 3.3392 0 TD
+ [(object)-337 (table)]TJ
+ /N92 1 Tf
+ 5.1175 0 TD
+ [(whose)-337 (entries)-336 (are)-336 (called)]TJ
+ /N94 1 Tf
+ 10.1758 0 TD
+ (handles)Tj
+ /N92 1 Tf
+ 3.1108 0 TD
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+ -21.7433 -1.1667 TD
+ [(f)10 (acilitate)-251 (object)-252 (compaction.)-251 (The)-251 (handle)-251 (address)-251 (of)-251 (an)-252 (object)-251 (remains)-251 (constant)-251 (during)-251 (the)-251 (object\325)55 (s)]TJ
+ T*
+ [(lifetime,)-335 (and)-336 (can)-336 (therefore)-336 (serv)15 (e)-336 (a)0 (s)-335 (a)-336 (unique)-335 (identi\336er)55 (.)-336 (A)-335 (global)-336 (table)-336 (called)-336 (the)]TJ
+ /N94 1 Tf
+ 33.18 0 TD
+ [(monitor)-336 (cac)16 (he)]TJ
+ /N92 1 Tf
+ -33.18 -1.1667 TD
+ [(maps)-341 (object)-341 (handle)-341 (addresses)-341 (to)-341 (monitor)-341 (structures)-341 (that)-342 (can)-341 (be)-341 (used)-341 (to)-341 (perform)-341 (the)-341 (actual)-341 (syn-)]TJ
+ T*
+ [(chronization)-242 (operations.)-242 (When)-243 (a)-242 (thread)-243 (synchronizes)-242 (on)-242 (an)-243 (object,)-243 (it)-242 (\336rst)-242 (ensures)-243 (that)-242 (the)-243 (monitor)]TJ
+ T*
+ [(cache)-309 (maps)-309 (the)-309 (object)-309 (to)-309 (a)-309 (monitor)41 (,)-309 (creating)-309 (and)-309 (installing)-308 (the)-309 (monitor)-309 (in)-309 (the)-309 (table)-309 (if)-309 (necessary)66 (.)]TJ
+ T*
+ [(This)-275 (approach)-275 (has)-274 (no)-275 (\336x)15 (ed)-275 (per)20 (-object)-275 (space)-275 (cost,)-275 (using)-275 (only)-274 (space)-276 (proportional)-274 (to)-275 (the)-275 (number)-275 (of)]TJ
+ T*
+ [(entries)-399 (in)-399 (the)-399 (monitor)-399 (cache.)-399 (Ho)25 (we)25 (v)15 (e)0 (r)40 (,)-398 (it)-399 (is)-399 (f)10 (airly)-399 (time-inef)25 (\336cient,)-399 (since)-398 (each)-399 (synchronization)]TJ
+ T*
+ [(operation)-311 (must)-311 (\336rst)-311 (do)-311 (\(at)-312 (least\))-311 (a)-311 (table)-311 (lookup)-311 (to)-311 (locate)-310 (the)-311 (monitor)-311 (associated)-311 (with)-311 (the)-310 (object.)]TJ
+ T*
+ [(Further)40 (,)-287 (i)0 (t)-288 (i)0 (s)-288 (not)-288 (v)15 (ery)-288 (scalable.)-288 (The)-288 (monitor)-288 (cache)-288 (is)-288 (a)-288 (global)-288 (data)-287 (structure)-288 (that)-287 (is)-288 (accessed)-288 (con-)]TJ
+ T*
+ [(currently)65 (.)-260 (T)79 (o)-260 (mak)10 (e)-260 (this)-261 (concurrent)-260 (access)-260 (safe,)-261 (the)-260 (monitor)-260 (cache)-260 (is)-260 (protected)-260 (by)-260 (a)-260 (lock.)-260 (Thus,)-260 (all)]TJ
+ T*
+ [(synchronization)-367 (operations)-367 (obtain)-367 (a)-368 (single)-367 (lock,)-368 (an)-367 (ob)15 (vious)-367 (source)-367 (of)-368 (contention.)-367 (The)-367 (monitor)]TJ
+ T*
+ (cache locking also adds some cost in the uncontended case.)Tj
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
+ %%EndPage
+ %%Page: 8 8
+ %%BeginPageSetup
+ userdict /pgsave save put
+ PDFVars begin PDF begin PDFVars/InitAll get exec
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+ 0 0 612 792 RC
+ 1 g
+ /N93 /ExtGState findRes gs
+ 1 i
+ 0 0 612 792 re
+ f 
+ BT
+ /N92 1 Tf
+ 12 0 0 12 303 34.17 Tm
+ 0 g
+ 0 Tc
+ 0 Tw
+ (5)Tj
+ -19.25 56.4858 TD
+ (Bacon)Tj
+ /N94 1 Tf
+ 2.8117 0 TD
+ [(et)-255 (al.)]TJ
+ /N92 1 Tf
+ 2.2625 0 TD
+ [([3])-256 (propose)-256 (a)-256 (cle)24 (v)15 (e)0 (r)-256 (scheme)-256 (moti)25 (v)25 (ated)-256 (by)-257 (man)15 (y)-257 (o)0 (f)-256 (the)-256 (same)-256 (concerns)-257 (as)-256 (ours.)-256 (In)-256 (this)]TJ
+ -5.0742 -1.1667 TD
+ [(design,)-274 (24)-274 (bits)-274 (of)-274 (each)-274 (object)-274 (header)-274 (are)-274 (de)25 (v)20 (oted)-274 (to)-274 (locking.)-273 (One)-275 (bit)-274 (indicates)-274 (whether)-274 (the)-274 (object)]TJ
+ T*
+ [(has)-295 (a)]TJ
+ /N94 1 Tf
+ 2.3683 0 TD
+ (thin)Tj
+ /N92 1 Tf
+ 1.8517 0 TD
+ (or)Tj
+ /N94 1 Tf
+ 1.1283 0 TD
+ (fat)Tj
+ /N92 1 Tf
+ 1.3517 0 TD
+ [(lock.)-295 (If)-295 (it)-296 (has)-295 (a)-296 (thin)-296 (lock,)-295 (then)-295 (all)-295 (necessary)-295 (locking)-296 (information)-295 (is)-295 (contained)-295 (in)]TJ
+ -6.7 -1.1667 TD
+ [(the)-276 (remaining)-276 (23)-277 (bits.)-277 (If)-276 (it)-276 (has)-277 (a)-277 (f)10 (at)-277 (lock,)-276 (then)-276 (the)-277 (remaining)-276 (23)-277 (bits)-277 (are)-276 (an)-276 (inde)15 (x)-277 (into)-276 (an)-277 (array)-276 (of)]TJ
+ T*
+ [(pointers)-257 (to)-257 (f)10 (a)0 (t)-257 (lock)-257 (structures)-258 (that,)-257 (much)-257 (lik)9 (e)-257 (monitors,)-257 (hold)-257 (the)-258 (necessary)-257 (data)-257 (for)-256 (the)-258 (synchroni-)]TJ
+ T*
+ [(zation)-305 (operations.)-305 (Thin)-305 (locks)-305 (are)-305 (used)-304 (as)-305 (long)-304 (as)-305 (the)-305 (lock)-305 (is)-305 (uncontended,)-305 (and)-305 (is)-305 (not)-304 (recursi)24 (v)15 (ely)]TJ
+ T*
+ [(lock)10 (ed)-294 (more)-294 (times)-294 (than)-295 (can)-294 (be)-294 (represented)-293 (in)-294 (a)-293 (count)-295 (\336eld)-294 (of)-294 (the)-294 (thin)-294 (lock;)-294 (if)-294 (either)-294 (condition)-294 (is)]TJ
+ T*
+ [(violated,)-340 (the)-340 (lock)-340 (representation)-340 (is)-340 (\322in\337ated.)70 (\323)-340 (This)-340 (design)-340 (does)-340 (well)-340 (at)-340 (optimizing)-341 (the)-340 (e)15 (xpected)]TJ
+ T*
+ [(common)-233 (case)-233 (of)-234 (uncontended)-233 (locking)-233 (and)-233 (unlocking.)-233 (Locking)-233 (requires)-233 (a)-234 (small)-233 (number)-233 (of)-234 (instruc-)]TJ
+ T*
+ [(tions,)-264 (with)-264 (only)-264 (one)-263 (atomic)-264 (instruction)-263 (in)-264 (the)-265 (f)10 (ast)-264 (path,)-264 (and)-263 (unlocking)-264 (requires)-264 (no)-263 (atomic)-264 (instruc-)]TJ
+ T*
+ [(tion. Ho)25 (we)25 (v)15 (e)0 (r)40 (,)0 ( thin locks lea)20 (v)15 (e)0 ( some issues to be addressed:)]TJ
+ /N95 1 Tf
+ 10 0 0 10 72 552 Tm
+ ( \245)Tj
+ /N94 1 Tf
+ 12 0 0 12 85.75 552 Tm
+ (Contention.)Tj
+ /N92 1 Tf
+ 4.9383 0 TD
+ [(When)-243 (there)-243 (is)-243 (contention)-244 (on)-243 (a)-243 (lock)-244 (for)-243 (the)-243 (\336rst)-244 (time,)-243 (all)-243 (threads)-244 (that)-243 (do)-243 (not)-243 (acquire)]TJ
+ -4.9383 -1.1667 TD
+ [(the)-240 (lock)-240 (must)]TJ
+ /N94 1 Tf
+ 5.6075 0 TD
+ [(b)20 (usy-wait)]TJ
+ /N92 1 Tf
+ 4.1083 0 TD
+ [(\(a.k.a.)-240 (spin\))-239 (until)-239 (the)-240 (lock)-239 (is)-240 (released.)-240 (Unbounded)-239 (b)20 (usy-w)10 (aiting)-239 (is)-240 (gen-)]TJ
+ -9.7158 -1.1667 TD
+ [(erally)-303 (undesirable)-303 (b)20 (ut,)-304 (as)-303 (the)-304 (authors)-303 (point)-303 (out,)-304 (b)20 (usy-w)10 (aiting)-303 (is)-304 (done)-303 (at)-304 (most)-302 (once)-304 (in)-303 (the)-304 (life-)]TJ
+ T*
+ [(time)-309 (of)-308 (a)-308 (g)0 (i)25 (v)15 (en)-308 (object.)-308 (Still,)-309 (it)-308 (w)10 (ould)-309 (not)-308 (be)-308 (hard)-308 (to)-309 (construct)-308 (a)-308 (program)-308 (that)-308 (does)-309 (contended)]TJ
+ T*
+ [(locking on man)15 (y short-li)26 (v)15 (ed objects, causing a great deal of b)21 (usy-w)10 (aiting.)]TJ
+ /N95 1 Tf
+ 10 0 0 10 72 476 Tm
+ ( \245)Tj
+ /N94 1 Tf
+ 12 0 0 12 85.75 476 Tm
+ [(Lac)21 (k)-395 (o)0 (f)-395 (de\337ation.)]TJ
+ /N92 1 Tf
+ 7.6367 0 TD
+ (Lock)Tj
+ /N94 1 Tf
+ 2.45 0 TD
+ (de\337ation)Tj
+ /N92 1 Tf
+ 3.8958 0 TD
+ [(is)-395 (not)-395 (discussed;)-395 (once)-395 (a)-395 (lock)-395 (becomes)-395 (f)10 (at,)-395 (it)-396 (remains)-395 (f)10 (at.)]TJ
+ -13.9825 -1.1667 TD
+ [(While)-245 (this)-246 (is)-245 (not)-245 (an)-245 (issue)-245 (for)-246 (most)-245 (programs,)-245 (one)-245 (could)-245 (imagine)-245 (a)-245 (long-li)25 (v)15 (e)0 (d)-245 (program)-245 (in)-245 (which)]TJ
+ T*
+ [(man)15 (y)-368 (long-li)25 (v)14 (e)0 (d)-368 (objects)-368 (are)-368 (lock)10 (ed)-368 (with)-368 (contention)-368 (at)-368 (some)-368 (point)-368 (in)-368 (their)-368 (lifetimes.)-367 (Absent)]TJ
+ T*
+ [(some)-381 (form)-380 (of)-380 (de\337ation,)-380 (such)-380 (a)-380 (program)-380 (w)10 (ould)-380 (consume)-381 (a)-380 (lar)18 (ge)-380 (amount)-381 (of)-380 (memory)-379 (for)-381 (f)10 (a)0 (t)]TJ
+ T*
+ (locks.)Tj
+ /N95 1 Tf
+ 10 0 0 10 72 400 Tm
+ ( \245)Tj
+ /N94 1 Tf
+ 12 0 0 12 85.75 400 Tm
+ [(Space)-359 (consumption.)]TJ
+ /N92 1 Tf
+ 8.4683 0 TD
+ [(Thin)-359 (locks)-360 (use)-359 (24)-360 (bits.)-359 (This)-359 (is)-360 (a)-359 (signi\336cant)-359 (o)15 (v)15 (erhead)-359 (since)-360 (the)-360 (a)20 (v)15 (erage)]TJ
+ -8.4683 -1.1667 TD
+ (object size for most programs is quite small [8].)Tj
+ -1.1458 -1.75 TD
+ [(In)-452 (other)-451 (related)-451 (w)9 (ork,)-451 (monitor)-452 (implementations)-451 (ha)21 (v)15 (e)-452 (been)-452 (proposed)-451 (that)-451 (e)15 (xploit)-452 (cooperati)25 (v)15 (e)]TJ
+ 0 -1.1667 TD
+ [(thread)-247 (scheduling)-247 ([14])-247 (or)-246 (mak)10 (e)-247 (special)-247 (pro)16 (vision)-247 (for)-246 (f)10 (aster)-247 (e)16 (x)15 (ecution)-247 (of)-247 (single-threaded)-247 (programs)]TJ
+ T*
+ [([21,)-252 (24].)-252 (As)-251 (we)-252 (ha)20 (v)15 (e)-252 (already)-252 (noted,)-251 (we)-252 (assume)-252 (preempti)25 (v)15 (e)-252 (scheduling,)-252 (and)-252 (desire)-252 (algorithms)-252 (that)]TJ
+ T*
+ [(w)10 (ork)-309 (well)-309 (for)-309 (both)-309 (single-)-308 (and)-309 (multi-threaded)-308 (programs,)-308 (so)-309 (we)-308 (shall)-308 (not)-309 (discuss)-308 (these)-309 (restricted)]TJ
+ T*
+ [(schemes further)55 (.)]TJ
+ 0 -1.75 TD
+ [(In)-242 ([4],)-241 (Bak)-242 (describes)-242 (ho)25 (w)-241 (a)0 (n)-242 (early)-242 (v)15 (ersion)-243 (of)-241 (Sun\325)55 (s)-242 (HotSpot\252)-242 (JVM)-242 (locks)-241 (objects)-242 (by)-242 (replacing)-241 (an)]TJ
+ 0 -1.1667 TD
+ [(object)-252 (header)-252 (w)10 (ord)-253 (with)-252 (a)-252 (pointer)-252 (to)-252 (an)-253 (e)16 (xternal)-252 (lock)-252 (structure,)-252 (displacing)-251 (the)-252 (original)-252 (contents)-252 (of)]TJ
+ T*
+ [(the)-270 (header)-269 (w)10 (ord)-269 (into)-270 (the)-269 (lock)-270 (structure.)-269 (T)80 (w)10 (o)-270 (l)0 (o)26 (w-order)-270 (bits)-269 (in)-269 (the)-269 (header)-270 (w)10 (ord)-269 (encode)-269 (its)-270 (format.)]TJ
+ T*
+ [(HotSpot)-361 (stack)-361 (allocates)-361 (lock)-360 (structures)-360 (for)-361 (ef)25 (\336cienc)15 (y)65 (.)-361 (Furthermore,)-361 (this)-361 (stack)-361 (allocation)-361 (allo)25 (ws)]TJ
+ T*
+ [(f)10 (ast)-388 (recursi)25 (v)15 (e)-389 (locking)-389 (by)-388 (enabling)-388 (ef)25 (\336cient)-389 (v)15 (eri\336cation)-388 (that)-388 (an)-388 (object)-388 (is)-389 (lock)10 (ed)-388 (by)-388 (the)-389 (current)]TJ
+ T*
+ [(thread:)-305 (if)-306 (the)-305 (lock)-305 (structure)-306 (address)-306 (is)-306 (suf)25 (\336ciently)-306 (close)-306 (to)-305 (the)-306 (current)-305 (stack)-306 (pointer)-306 (to)-306 (guarantee)]TJ
+ T*
+ [(membership)-276 (in)-276 (the)-276 (same)-277 (thread)-276 (stack,)-277 (the)-276 (current)-276 (thread)-276 (must)-276 (be)-277 (the)-276 (lock)-276 (o)25 (wner)56 (.)-277 (I)0 (n)-276 (non-preemp-)]TJ
+ T*
+ [(ti)25 (v)15 (e)-293 (thread)-293 (systems,)-292 (locking)-292 (and)-292 (unlocking)-292 (can)-292 (be)-293 (implemented)-292 (straightforw)10 (ardly)65 (.)-292 (I)0 (n)-292 (preempti)25 (v)15 (e)]TJ
+ T*
+ [(systems,)-344 (a)-343 (more)-343 (complicated)-343 (test-and-set)-344 (protocol)-343 (on)-343 (one)-343 (of)-344 (the)-344 (bits)-344 (in)-344 (the)-343 (header)-344 (w)10 (ord)-344 (grants)]TJ
+ T*
+ [(e)15 (xclusi)25 (v)15 (e)0 ( access to at most one thread; other threads b)21 (usy-w)10 (ait for their turn.)]TJ
+ 0 -1.75 TD
+ [(W)80 (e)-246 (borro)25 (w)-246 (HotSpot\325)55 (s)-246 (idea)-246 (of)-246 (displacing)-246 (a)-246 (header)-247 (w)10 (ord)-246 (and)-246 (using)-246 (some)-246 (bits)-247 (of)-246 (the)-246 (w)10 (ord)-246 (to)-247 (encode)]TJ
+ 0 -1.1667 TD
+ [(its)-237 (format)-236 (and)-236 (the)-236 (lock)-236 (state.)-236 (W)80 (e)-236 (use)-236 (a)-236 (dif)24 (ferent)-235 (allocation)-237 (scheme)-236 (to)-236 (support)-237 (non-block-structured)]TJ
+ T*
+ [(synchronization and emplo)11 (y a b)20 (usy-w)10 (ait-free protocol to protect the header w)11 (ord.)]TJ
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
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+ userdict /pgsave save put
+ PDFVars begin PDF begin PDFVars/InitAll get exec
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+ 0 0 612 792 re
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+ BT
+ /N92 1 Tf
+ 12 0 0 12 303 34.17 Tm
+ 0 g
+ 0 Tc
+ 0 Tw
+ (6)Tj
+ /N91 1 Tf
+ 16 0 0 16 72 709.33 Tm
+ (4  Our algorithm)Tj
+ /N92 1 Tf
+ 12 0 0 12 72 686 Tm
+ [(In)-250 (an)15 (y)-251 (concurrent)-250 (en)40 (vironment,)-250 (there)-250 (must)-251 (be)-251 (some)-251 (protocol)-250 (observ)15 (ed)-251 (by)-251 (threads)-250 (as)-250 (the)15 (y)-250 (manipu-)]TJ
+ 0 -1.1667 TD
+ [(late)-317 (the)]TJ
+ /N94 1 Tf
+ 3.3 0 TD
+ [(sync)15 (hr)45 (onization)-317 (data)]TJ
+ /N92 1 Tf
+ 8.7408 0 TD
+ [(of)-317 (objects,)-317 (that)-317 (is,)-317 (the)-316 (data)-317 (structures)-317 (that)-317 (manage)-317 (synchronization)]TJ
+ -12.0408 -1.1667 TD
+ [(operations.)-302 (T)80 (ypically)65 (,)-302 (the)-302 (protocol)-303 (speci\336es)-302 (when)-302 (a)-303 (thread)-303 (may)-302 (access)-302 (or)-303 (manipulate)-302 (an)-303 (object\325)55 (s)]TJ
+ T*
+ [(synchronization)-272 (data.)-273 (F)15 (o)0 (r)-273 (e)15 (xample,)-272 (the)-273 (thin-locks)-272 (approach)-272 (relies)-273 (on)-272 (an)-273 (in)41 (v)25 (ariant)-273 (whereby)-273 (only)-273 (a)]TJ
+ T*
+ [(thread)-492 (o)25 (wning)-492 (the)-491 (lock)-491 (on)-492 (an)-492 (object)-492 (may)-491 (modify)-492 (that)-492 (object\325)55 (s)-492 (synchronization)-491 (data.)-492 (Other)]TJ
+ T*
+ [(approaches,)-308 (lik)9 (e)-308 (ours,)-309 (allo)25 (w)-309 (a)0 (n)15 (y)-309 (thread)-308 (to)-309 (update)-309 (this)-308 (information.)-309 (The)-309 (k)10 (e)15 (y)-309 (t)0 (o)-309 (our)-309 (approach)-309 (is)-309 (a)]TJ
+ T*
+ [(time-)-296 (and)-297 (space-ef)25 (\336cient)-297 (meta-lock)-297 (associated)-296 (with)-297 (the)-296 (synchronization)-297 (data)-297 (of)-296 (each)-297 (object.)-297 (The)]TJ
+ T*
+ (typical pattern for synchronization operations in our system is:)Tj
+ 1.1458 -1.6667 TD
+ [(1.)-228 (Obtain)-229 (the)-229 (object\325)55 (s)-229 (meta-lock)-228 (to)-229 (ensure)-228 (e)15 (xclusi)25 (v)15 (e)-229 (access)-228 (to)-229 (the)-229 (object\325)55 (s)-228 (synchronization)-228 (data.)]TJ
+ 0 -1.4167 TD
+ [(2. Manipulate the synchronization data of that object. This operation sh\
+ ould be f)11 (ast.)]TJ
+ T*
+ [(3. Release or hand of)25 (f the object\325)55 (s meta-lock.)]TJ
+ -1.1458 -1.75 TD
+ [(Meta-locks)-462 (play)-463 (a)-463 (similar)-463 (role)-463 (as)-463 (the)-463 (auxiliary)-462 (spin-locks)-463 (seen)-463 (in)-463 (man)15 (y)-462 (implementations)-463 (of)]TJ
+ 0 -1.1667 TD
+ [(POSIX)-372 (threads)-373 ([6,)-372 (17].)-372 (These)-372 (spin-locks)-372 (pro)15 (vide)-372 (brief)-372 (e)15 (xclusi)26 (v)15 (e)-373 (access)-372 (to)-372 (the)-372 (synchronization)]TJ
+ T*
+ [(state maintained in records representing programmer)21 (-le)25 (v)15 (el mute)15 (x)15 (es and condition v)25 (ariables.)]TJ
+ 0 -1.75 TD
+ [(W)80 (e)-300 (shall)-299 (use)-300 (the)-300 (term)-300 (\322monitor)20 (-lock\323)-300 (to)-300 (denote)-300 (the)-300 (lock)-300 (abstraction)-299 (e)15 (xported)-300 (by)-300 (the)-300 (Ja)20 (v)25 (a)-300 (virtual)]TJ
+ 0 -1.1667 TD
+ [(machine)-358 (to)-358 (a)20 (v)20 (oid)-358 (confusion)-357 (with)-358 (the)-358 (meta-lock)-357 (used)-358 (in)-358 (its)-357 (implementation.)-357 (Because)-358 (meta-lock)]TJ
+ T*
+ [(acquisition)-353 (occurs)-354 (in)-354 (FIFO)-354 (order)40 (,)-353 (the)-354 (abo)15 (v)15 (e)-354 (pattern)-354 (allo)25 (ws)-354 (a)-354 (number)-354 (of)-353 (f)10 (airness)-354 (policies)-354 (at)-354 (the)]TJ
+ T*
+ [(monitor)-306 (le)25 (v)15 (el.)-306 (The)-307 (rest)-307 (of)-306 (this)-307 (section)-307 (describes)-306 (our)-306 (algorithm)-307 (in)-307 (detail:)-306 (Section)-307 (4.1)-307 (presents)-307 (the)]TJ
+ T*
+ [(data)-298 (structures)-298 (in)40 (v)20 (olv)15 (ed,)-298 (Section)-298 (4.2)-298 (the)-298 (meta-lock)-298 (algorithm,)-297 (Section)-298 (4.3)-298 (the)-298 (implementation)-297 (of)]TJ
+ T*
+ [(the)-377 (monitor)20 (-le)25 (v)15 (e)0 (l)-377 (lock)-377 (and)-378 (unlock)-378 (operations,)-377 (and)-377 (Section)-377 (4.4)-377 (the)-378 (implementation)-377 (of)-378 (w)10 (ait)-377 (and)]TJ
+ T*
+ [(notify)65 (.)]TJ
+ /N91 1 Tf
+ 14 0 0 14 72 347.67 Tm
+ [(4.1  Data structur)18 (es)]TJ
+ /N92 1 Tf
+ 12 0 0 12 72 323 Tm
+ [(Synchronization)-307 (in)40 (v)20 (olv)16 (es)-308 (three)-308 (entities:)-307 (threads,)-308 (objects,)-308 (and)-308 (lock)-307 (records.)-308 (W)80 (e)-308 (describe)-307 (the)-308 (rele-)]TJ
+ T*
+ [(v)25 (ant)-310 (parts)-311 (of)-310 (the)-310 (data)-311 (structures)-311 (that)-310 (implement)-311 (them)-311 (and)-310 (ho)25 (w)-311 (the)15 (y)-310 (interact)-311 (during)-311 (synchroniza-)]TJ
+ T*
+ (tion.)Tj
+ /N94 1 Tf
+ 0 -1.75 TD
+ [(Thr)37 (eads)]TJ
+ /N92 1 Tf
+ 3.2408 0 TD
+ [(.)-246 (W)80 (e)-246 (call)-246 (the)-245 (data)-246 (structure)-246 (that)-246 (holds)-245 (thread-speci\336c)-246 (state)-245 (an)]TJ
+ /N94 1 Tf
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+ [(e)20 (xecution)-246 (en)40 (vir)45 (onment)]TJ
+ /N92 1 Tf
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+ (\()Tj
+ /N95 1 Tf
+ 0.3325 0 TD
+ (EE)Tj
+ /N92 1 Tf
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+ (\).)Tj
+ -38.4167 -1.1667 TD
+ (Since)Tj
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+ 2.4683 0 TD
+ (EE)Tj
+ /N92 1 Tf
+ 1.2 0 TD
+ [(s)-246 (and)-246 (threads)-246 (correspond)-246 (one)-246 (to)-246 (one,)]TJ
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+ (EE)Tj
+ /N92 1 Tf
+ 1.4467 0 TD
+ [(addresses)-245 (are)-246 (well-suited)-246 (as)-246 (unique)-246 (thread)-246 (iden-)]TJ
+ -19.9175 -1.1667 TD
+ [(ti\336ers.)-249 (Figure)-250 (1)-250 (sho)25 (ws)-250 (the)-250 (\336elds)-250 (in)]TJ
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+ [(s)-249 (that)-250 (the)-250 (synchronization)-249 (code)-249 (uses)-250 (as)-249 (well)-250 (as)-249 (an)-249 (initializa-)]TJ
+ -15.2292 -1.1667 TD
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+ (EE)Tj
+ /N92 1 Tf
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+ -3.6508 -1.1667 TD
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+ T*
+ (the same object.)Tj
+ /N94 1 Tf
+ 0 -1.75 TD
+ (Objects)Tj
+ /N92 1 Tf
+ 3.055 0 TD
+ [(.)-265 (Figure)-250 (2)-265 (sho)25 (ws)-265 (the)-265 (object)-265 (layout)-265 (in)-264 (EVM.)-265 (Because)-264 (e)25 (v)15 (ery)-265 (object)-265 (may)-265 (potentially)-265 (be)-264 (used)]TJ
+ -3.055 -1.1667 TD
+ [(for)-350 (synchronization,)-349 (it)-350 (is)-350 (critical)-350 (to)-350 (minimize)-349 (the)-350 (per)20 (-object)-350 (space)-350 (o)15 (v)15 (erhead.)-349 (Objects)-350 (ha)20 (v)15 (e)-349 (tw)10 (o-)]TJ
+ T*
+ [(w)10 (ord)-313 (headers.)-312 (The)-312 (\336rst)-312 (w)9 (ord)-312 (points)-312 (to)-313 (the)-312 (object\325)55 (s)-312 (class.)-313 (Only)-312 (the)-313 (second)-312 (w)9 (ord)-312 (is)-313 (used)-312 (for)-313 (syn-)]TJ
+ T*
+ [(chronization,)-284 (b)21 (u)0 (t)-284 (i)0 (t)-284 (serv)15 (es)-284 (other)-284 (purposes)-284 (as)-284 (well,)-284 (such)-284 (as)-284 (holding)-284 (a)-284 (hash)-284 (code)]TJ
+ 9.6 0 0 9.6 450.48 131.8 Tm
+ (2)Tj
+ 12 0 0 12 458.69 127 Tm
+ [(and)-283 (garbage-col-)]TJ
+ ET
+ 0 G
+ 2 J
+ 0 j
+ 0.36 w
+ 3.86 M
+ []0 d
+ 204 86 m
+ 72 86 l
+ S 
+ BT
+ 10 0 0 10 72 71.33 Tm
+ [(2.  EVM uses a handle-less cop)9 (ying memory system, so object or handle addresses cannot be used as hash\
+  codes.)]TJ
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
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+ userdict /pgsave save put
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+ BT
+ /N92 1 Tf
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+ 0 g
+ 0 Tc
+ 0 Tw
+ (7)Tj
+ -19.25 32.1942 TD
+ [(lector)-284 (age)-284 (information,)-283 (so)-284 (we)-283 (call)-283 (it)-284 (the)]TJ
+ /N94 1 Tf
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+ (multi-use)Tj
+ /N92 1 Tf
+ 4.0058 0 TD
+ [(w)10 (ord.)-284 (W)80 (e)-283 (emplo)10 (y)-284 (a)]TJ
+ /N94 1 Tf
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+ [(header)-283 (wor)37 (d)-284 (displacement)]TJ
+ /N92 1 Tf
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+ [(technique)-299 (in)41 (v)15 (ented)-299 (by)-299 (our)-299 (colleague)-299 (Lars)-299 (Bak)-299 ([4].)-299 (The)-299 (tw)10 (o)-299 (least)-299 (signi\336cant)-299 (bits)-299 (in)-299 (the)-299 (multi-use)]TJ
+ T*
+ [(w)10 (ord,)-389 (called)-389 (the)]TJ
+ /N94 1 Tf
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+ [(loc)20 (k)-389 (bits)]TJ
+ /N92 1 Tf
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+ [(,)-389 (hold)-389 (the)]TJ
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+ [(loc)20 (k)-389 (state)10 (,)]TJ
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+ [(which)-388 (serv)15 (e)-389 (a)0 (s)-389 (a)-389 (format)-389 (indicator)-388 (and)-388 (simulta-)]TJ
+ -19.52 -1.1667 TD
+ [(neously)-255 (encode)-254 (meta-lock)-254 (information)-254 (for)-255 (the)-255 (object.)-254 (Figure)-250 (3)-254 (sho)25 (ws)-255 (the)-254 (four)-255 (possible)-254 (lock)-255 (states)]TJ
+ T*
+ [(and)-244 (their)-244 (formats.)-245 (Objects)-245 (are)-244 (created)-245 (in)-244 (the)]TJ
+ /N95 1 Tf
+ 17.7017 0 TD
+ (NEUTRAL)Tj
+ /N92 1 Tf
+ 4.445 0 TD
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+ -22.1467 -1.1667 TD
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+ /N95 1 Tf
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+ [(once)-376 (synchronization)-376 (ceases.)-376 (A)-376 (monitor)21 (-lock)10 (ed)-376 (object)-377 (is)-375 (in)-376 (the)]TJ
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+ /N92 1 Tf
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+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
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+ %%Page: 12 12
+ %%BeginPageSetup
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+ T*
+ [(appropriate)-315 (to)-314 (the)-315 (ne)25 (w)-315 (state)-315 (of)-314 (the)-315 (synchronization)-314 (data.)-315 (This)-315 (ne)25 (w)-315 (v)25 (alue)-315 (may)-315 (be)-314 (an)15 (y)-315 (non-)]TJ
+ /N95 1 Tf
+ 36.6 0 TD
+ (BUSY)Tj
+ /N92 1 Tf
+ -36.6 -1.1667 TD
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+ /N95 1 Tf
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+ (NEUTRAL)Tj
+ /N92 1 Tf
+ 4.555 0 TD
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+ -4.555 -1.1667 TD
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+ /N94 1 Tf
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+ /N92 1 Tf
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+ -11.4 -1.1428 TD
+ (BitField busyBits = ee | BUSY;)Tj
+ T*
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+ -2.4 -1.1429 TD
+ (})Tj
+ /N92 1 Tf
+ 12 0 0 12 195.77 458.33 Tm
+ [(Figure 5. F)16 (ast paths for meta-lock operations)]TJ
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+ 0 Tc
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+ /N94 1 Tf
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+ [(to)-271 (ensure)-271 (that)-272 (the)-270 (threads)-271 (participating)-271 (in)-271 (the)-270 (hand-of)25 (f)-271 (update)-271 (the)-271 (other)-271 (\336elds)-271 (in)-271 (the)-270 (correct)-271 (order)55 (.)]TJ
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+ /N92 1 Tf
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+ -1.2 -1.1667 TD
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+ /N95 1 Tf
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+ /N95 1 Tf
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+ T*
+ (the meta-lock.)Tj
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+ T*
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+ 0 -1.1667 TD
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+ T*
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+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
+ %%EndPage
+ %%Page: 14 14
+ %%BeginPageSetup
+ userdict /pgsave save put
+ PDFVars begin PDF begin PDFVars/InitAll get exec
+ %%EndPageSetup
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+ BT
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+ 0 -1.1667 TD
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+ T*
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+ T*
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+ T*
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+ T*
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+ T*
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+ T*
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+ /N95 1 Tf
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+ 0 -1.1667 TD
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+ T*
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+ T*
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+ -17.2292 -1.1667 TD
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+ T*
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+ T*
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+ /N95 1 Tf
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+ /N92 1 Tf
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+ -16.6842 -1.1667 TD
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+ /N95 1 Tf
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+ /N95 1 Tf
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+ 15 -1.25 TD
+ [(BitField)-544 (releaseBits\))-544 ({)]TJ
+ -13.8 -1.25 TD
+ (/* We are in a race with our successor to)Tj
+ 1.8 -1.25 TD
+ (lock ee->metaLockMutex; the winner of)Tj
+ T*
+ (the race waits for the loser. */)Tj
+ -1.8 -1.25 TD
+ (mutexLock\(&ee->metaLockMutex\);)Tj
+ T*
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+ 1.2 -1.25 TD
+ (/* Lost the race: */)Tj
+ T*
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+ T*
+ (assert\(!ee->bitsForGrab\);)Tj
+ T*
+ (assert\(!ee->succEE->gotMetaLockSlow\);)Tj
+ T*
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+ T*
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+ T*
+ (ee->succEE = NULL;)Tj
+ T*
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+ -1.2 -1.25 TD
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+ (/* Won the race: */)Tj
+ T*
+ (ee->metaLockBits = releaseBits;)Tj
+ T*
+ [(ee->bitsForGrab)-1200 (= TRUE;)]TJ
+ T*
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+ 1.2 -1.25 TD
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+ 7.2 -1.25 TD
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+ -8.4 -1.25 TD
+ (} while \(ee->bitsForGrab\);)Tj
+ -1.2 -1.25 TD
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+ T*
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+ -1.2 -1.25 TD
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+ -29.125 31.25 TD
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+ 15 -1.25 TD
+ (BitField predBits\) {)Tj
+ -13.8 -1.25 TD
+ (BitField bits;)Tj
+ T*
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+ T*
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+ T*
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+ T*
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+ 1.2 -1.25 TD
+ (/* Won the race: */)Tj
+ T*
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+ T*
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+ 1.2 -1.25 TD
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+ 7.2 -1.25 TD
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+ -8.4 -1.25 TD
+ (} while \(!ee->gotMetaLockSlow\);)Tj
+ T*
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+ T*
+ (bits = ee->metaLockBits;)Tj
+ -1.2 -1.25 TD
+ (} else {)Tj
+ 1.2 -1.25 TD
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+ T*
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+ T*
+ (condvarSignal\(&predEE->metaLockCondvar\);)Tj
+ -1.2 -1.25 TD
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+ T*
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+ T*
+ (return bits;)Tj
+ -1.2 -1.25 TD
+ (})Tj
+ /N92 1 Tf
+ 12 0 0 12 196 433.67 Tm
+ [(Figure 6. Slo)25 (w paths for meta-lock operations)]TJ
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
+ %%EndPage
+ %%Page: 15 15
+ %%BeginPageSetup
+ userdict /pgsave save put
+ PDFVars begin PDF begin PDFVars/InitAll get exec
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+ BT
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+ 0 -1.1667 TD
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+ /N95 1 Tf
+ 20.7758 0 TD
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+ /N92 1 Tf
+ 6.3417 0 TD
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+ -27.1175 -1.1667 TD
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+ T*
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+ T*
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+ /N95 1 Tf
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+ /N92 1 Tf
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+ -9.375 -1.1667 TD
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+ T*
+ [(the)-238 (releasing)-238 (thread)-238 (does)-238 (not)-239 (gi)26 (v)14 (e)-238 (the)-238 (monitor)20 (-lock)-238 (to)-238 (a)-238 (w)10 (aiting)-239 (thread)-238 (b)20 (u)0 (t)-238 (merely)-238 (in)40 (vites)-238 (the)-238 (w)10 (ait-)]TJ
+ T*
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+ (ing thread to re-attempt the acquisition.)Tj
+ /N95 1 Tf
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+ 1.2 -1.1429 TD
+ [(BitField)-1201 (r)-3000 (=)0 ( getMetaLock\(ee, obj\);)]TJ
+ T*
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+ T*
+ (if \(state == NEUTRAL\) {)Tj
+ 1.2 -1.1429 TD
+ (/* Establish locking by this thread. */)Tj
+ T*
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+ T*
+ (lr->storedBits = r;)Tj
+ T*
+ (releaseMetaLock\(ee, obj, lr | LOCKED\);)Tj
+ -1.2 -1.1428 TD
+ (} else if \(state == LOCKED\) {)Tj
+ 1.2 -1.1429 TD
+ (LockRecord *ownerLR = lockRecord\(r\);)Tj
+ T*
+ (if \(ownerLR->owner == ee\) {)Tj
+ 1.2014 -1.1429 TD
+ (/* Recursive locking. */)Tj
+ T*
+ (ownerLR->lockCount++;)Tj
+ T*
+ (releaseMetaLock\(ee, obj, r\);)Tj
+ -1.2014 -1.1429 TD
+ (} else {)Tj
+ 1.2014 -1.1429 TD
+ (LockRecord *lr = allocLockRecord\(ee\);)Tj
+ T*
+ (ownerLR->queue = appendToQueue\(ownerLR->queue,)Tj
+ 18.6 -1.1428 TD
+ (lr\);)Tj
+ -18.6 -1.1429 TD
+ (monitorEnterSlow\(ee, obj, r\);)Tj
+ -1.2014 -1.1429 TD
+ (})Tj
+ -1.2 -1.1429 TD
+ (} else if \(state == WAITERS\) {)Tj
+ 1.2 -1.1429 TD
+ (/* obj is unlocked but has threads waiting)Tj
+ 1.8 -1.1429 TD
+ (for notification. */)Tj
+ -1.8 -1.1429 TD
+ (LockRecord *lr = allocLockRecord\(ee\);)Tj
+ T*
+ (LockRecord *firstWaiterLR = lockRecord\(r\);)Tj
+ T*
+ [(lr->queue)-3600 (= firstWaiterLR;)]TJ
+ T*
+ (lr->storedBits = firstWaiterLR->storedBits;)Tj
+ T*
+ (releaseMetaLock\(ee, obj, lr | LOCKED\);)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ T*
+ (return TRUE;)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ 33.47 34.3871 TD
+ (bool_t monitorExit\(ExecEnv *ee, Object *obj\) {)Tj
+ 1.2 -1.1429 TD
+ [(BitField)-2400 (r)-4200 (=)0 ( getMetaLock\(ee, obj\);)]TJ
+ T*
+ (LockRecord *ownerLR = lockRecord\(r\);)Tj
+ T*
+ [(LockState)-1800 (state)-1800 (= lockState\(r\);)]TJ
+ T*
+ (if \(state == LOCKED && ownerLR->owner == ee\) {)Tj
+ 1.2 -1.1429 TD
+ (assert\(ownerLR->lockCount >= 1\);)Tj
+ T*
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+ 1.2 -1.1429 TD
+ (/* Last release: will not have lock)Tj
+ 1.8 -1.1429 TD
+ (after this operation. */)Tj
+ -1.8 -1.1429 TD
+ (if \(ownerLR->queue == NULL\) {)Tj
+ 1.2 -1.1429 TD
+ (/* No-one waiting. */)Tj
+ T*
+ (assert\(lockState\(ownerLR->storedBits\))Tj
+ 4.8 -1.1429 TD
+ (== NEUTRAL\);)Tj
+ -4.8 -1.1429 TD
+ (releaseMetaLock\(ee, obj,)Tj
+ 9.6 -1.1429 TD
+ (ownerLR->storedBits\);)Tj
+ -10.8 -1.1429 TD
+ (} else {)Tj
+ 1.2 -1.1429 TD
+ (/* There is a queue. Release)Tj
+ 1.8 -1.1429 TD
+ (with wakeup call. */)Tj
+ -1.8 -1.1429 TD
+ (ownerLR->queue->storedBits =)Tj
+ 12 -1.1429 TD
+ (ownerLR->storedBits;)Tj
+ -12 -1.1429 TD
+ (monitorExitSlow\(ee, obj, ownerLR->queue\);)Tj
+ T*
+ (ownerLR->queue = NULL;)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ T*
+ (recycleLockRecord\(ee, ownerLR\);)Tj
+ -1.2 -1.1429 TD
+ (} else {)Tj
+ 1.2 -1.1429 TD
+ (/* Still has lock after this. */)Tj
+ T*
+ (ownerLR->lockCount--;)Tj
+ T*
+ (releaseMetaLock\(ee, obj, r\);)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ -1.2 -1.1429 TD
+ (} else {)Tj
+ 1.2 -1.1429 TD
+ (releaseMetaLock\(ee, obj, r\);)Tj
+ T*
+ (throwIllegalMonitorStateException\(\);)Tj
+ T*
+ (return FALSE;)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ T*
+ (return TRUE;)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ /N92 1 Tf
+ 12 0 0 12 191.05 413.5 Tm
+ [(Figure 7. F)15 (ast paths for monitor)20 (-lock operations)]TJ
+ /N95 1 Tf
+ 7 0 0 7 81 368.43 Tm
+ (void monitorEnterSlow\(ExecEnv *ee, Object *obj,)Tj
+ 13.2 -1.1429 TD
+ (BitField r\) {)Tj
+ -12 -1.1429 TD
+ (LockRecord *lr;)Tj
+ T*
+ (while \(lockState\(r\) == LOCKED\) {)Tj
+ 1.2 -1.1429 TD
+ (mutexLock\(&ee->monitorLockMutex\);)Tj
+ T*
+ (releaseMetaLock\(ee, obj, r\);)Tj
+ T*
+ (condvarWait\(&ee->monitorLockCondvar,)Tj
+ 7.2 -1.1429 TD
+ (&ee->monitorLockMutex\);)Tj
+ -7.2 -1.1429 TD
+ (mutexUnlock\(&ee->monitorLockMutex\);)Tj
+ T*
+ (r = getMetaLock\(ee, obj\);)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ T*
+ (assert\(lockState\(r\) == WAITERS\);)Tj
+ T*
+ (lr = moveMyLRToFront\(ee, lockRecord\(r\)\);)Tj
+ T*
+ (releaseMetaLock\(ee, obj, lr | LOCKED\);)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ 33.4286 15.9386 TD
+ (void monitorExitSlow\(ExecEnv *ee, Object *obj,)Tj
+ 12.6 -1.1429 TD
+ (LockRecord *lr\) {)Tj
+ -11.4 -1.1429 TD
+ (ExecEnv *wakeEE = wakeupEE\(lr\);)Tj
+ T*
+ (if \(wakeEE\) {)Tj
+ 1.2 -1.1429 TD
+ (mutexLock\(&wakeEE->monitorLockMutex\);)Tj
+ T*
+ (releaseMetaLock\(ee, obj, lr | WAITERS\);)Tj
+ T*
+ (condvarSignal\(&wakeEE->monitorLockCondvar\);)Tj
+ T*
+ (mutexUnlock\(&wakeEE->monitorLockMutex\);)Tj
+ -1.2 -1.1429 TD
+ (} else {)Tj
+ 1.2 -1.1429 TD
+ (releaseMetaLock\(ee, obj, lr | WAITERS\);)Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ -1.2 -1.1429 TD
+ (})Tj
+ /N92 1 Tf
+ 12 0 0 12 188.78 239.67 Tm
+ [(Figure 8. Slo)25 (ws path for monitor)21 (-lock operations)]TJ
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
+ %%EndPage
+ %%Page: 16 16
+ %%BeginPageSetup
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+ [(Figure)-250 (9)-248 (sho)25 (ws)-247 (the)-247 (remaining)-247 (tw)10 (o)-247 (monitor)-248 (operations:)-247 (w)9 (ait)-247 (and)-248 (notify)65 (.)-248 (The)-247 (Ja)20 (v)25 (a)-247 (language)-247 (speci\336-)]TJ
+ 0 -1.1667 TD
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+ T*
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+ /N95 1 Tf
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+ [(causing)-353 (serialization)-353 (of)-354 (monitor)-353 (cache)-354 (operations)-353 (and)-353 (resulting)-353 (scalability)-354 (bottlenecks.)-353 (Periodi-)]TJ
+ T*
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+ /N92 1 Tf
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+ [(\).)-267 (Lock)-267 (record)-267 (allocation)-267 (is)-266 (optimized)-266 (to)]TJ
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+ /N95 1 Tf
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+ [(retries)-317 (the)-317 (operation.)-318 (Threads)-316 (start)-317 (with)-318 (8)-317 (free)-318 (lock)-317 (records)-317 (and)-318 (add)-317 (an)-318 (e)16 (xponentially)-317 (increasing)]TJ
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+ 0 -1.1667 TD
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+ T*
+ [(a)-234 (g)0 (i)25 (v)15 (en)-235 (thread)-234 (only)-234 (gro)25 (ws;)-235 (there)-234 (is)-235 (no)-235 (pro)15 (vision)-234 (for)-235 (remo)15 (ving)-234 (lock)-235 (records)-234 (from)-234 (a)-235 (thread\325)55 (s)-235 (free)-234 (list)]TJ
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+ T*
+ [(mark\323)-321 (of)-320 (allocated)-321 (lock)-320 (records)-321 (is)-320 (limited)-320 (by)-321 (the)-321 (product)-320 (of)-321 (the)-320 (thread)-321 (stack)-321 (size)-321 (and)-320 (the)-320 (maxi-)]TJ
+ T*
+ [(mum)-245 (le)15 (xical)-245 (nesting)-245 (depth)-245 (of)-245 (synchronized)-244 (statements)-245 (\(at)-245 (least)-245 (for)-246 (bytecode)-245 (created)-245 (by)-245 (compiling)]TJ
+ T*
+ [(Ja)20 (v)25 (a)-373 (language)-373 (source)-372 (code,)-374 (as)-373 (discussed)-373 (in)-373 (Section)-373 (2.2\).)-374 (If)-372 (we)-373 (wished)-374 (to)-373 (add)-373 (a)-374 (mechanism)-372 (to)]TJ
+ T*
+ [(return)-238 (lock)-239 (records)-238 (on)-238 (free)-238 (lists)-238 (to)-238 (the)-238 (global)-238 (memory)-238 (pool,)-238 (it)-238 (w)9 (ould)-238 (be)-238 (a)-238 (simple)-239 (matter)-237 (to)-239 (do)-238 (so)-238 (as)]TJ
+ T*
+ [(part)-257 (of)-257 (garbage)-257 (collection,)-257 (as)-258 (long)-257 (as)-258 (we)-257 (can)-258 (guarantee)-257 (that)-257 (no)-257 (thread)-258 (is)-257 (accessing)-257 (the)-258 (lock)-257 (record)]TJ
+ T*
+ [(free)-261 (list)-262 (during)-261 (garbage)-262 (collection.)-261 (Our)-262 (system)-261 (has)-261 (a)-261 (general)-261 (mechanism)-261 (for)-261 (restricting)-261 (when)-261 (gar-)]TJ
+ T*
+ [(bage collection occurs that can be used to pro)16 (vide this guarantee.)]TJ
+ /N91 1 Tf
+ 14 0 0 14 72 275.67 Tm
+ (6.2  Extra fast locking and unlocking of uncontended objects)Tj
+ /N92 1 Tf
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+ [(W)80 (e)-238 (can)-238 (optimize)-238 (the)-238 (algorithm)-238 (further)-238 (in)-239 (the)-238 (case)-238 (of)-239 (uncontended)-238 (objects.)-238 (This)-239 (optimization)-238 (fuses)]TJ
+ T*
+ [(the)-390 (meta-lock)-389 (and)-389 (monitor)21 (-lock)-390 (operations)-389 (into)-390 (a)-389 (single)-389 (step.)-390 (W)40 (ith)-389 (this)-390 (optimization,)-389 (a)-389 (thread)]TJ
+ T*
+ [(attempting)-293 (to)-294 (lock)-293 (an)-294 (object)-293 (reads)-293 (the)-294 (object\325)55 (s)-293 (multi-use)-293 (w)10 (ord.)-294 (If)-294 (the)-293 (object\325)55 (s)-293 (lock)-293 (state)-294 (is)]TJ
+ /N95 1 Tf
+ 36.6 0 TD
+ (NEU-)Tj
+ -36.6 -1.1667 TD
+ (TRAL)Tj
+ /N92 1 Tf
+ 2.4 0 TD
+ [(,)-276 (then)-276 (an)-276 (\322e)16 (xtra)-277 (f)11 (ast\323)-276 (path)-276 (is)-276 (tried.)-275 (The)-277 (thread)-276 (copies)-276 (the)-275 (hash)-276 (and)-276 (age)-276 (bits)-276 (into)-276 (a)-276 (fresh)-276 (lock)]TJ
+ -2.4 -1.1667 TD
+ [(record)-233 (and)-233 (b)20 (uilds)-234 (a)-233 (n)0 (e)25 (w)-234 (multi-use)-233 (v)25 (alue)-233 (containing)-234 (the)-234 (lock)-234 (record)-233 (address)-233 (and)-233 (the)]TJ
+ /N95 1 Tf
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+ -3.0575 -1.1667 TD
+ [(not)-279 (changed)-279 (since)-280 (it)-280 (w)10 (a)0 (s)-280 (read.)-280 (If)-280 (the)]TJ
+ /N95 1 Tf
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+ -16.9433 -1.1667 TD
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+ T*
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+ T*
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+ 0 -1.75 TD
+ [(A)-287 (similar)-287 (e)15 (xtra)-287 (f)10 (ast)-286 (path)-287 (for)-287 (unlocking)-286 (is)-287 (slightly)-286 (more)-287 (complicated.)-287 (When)-287 (the)-287 (e)16 (xtra)-287 (f)11 (ast)-287 (locking)]TJ
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+ T*
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+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
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+ 0 Tc
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+ -19 56.4858 TD
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+ 0 -1.1667 TD
+ [(object)-363 (back)-362 (to)-363 (its)-362 (original)-362 (contents,)-363 (b)20 (u)0 (t)-363 (only)-362 (if)-362 (the)-363 (queue)-363 (\336eld)-362 (of)-363 (the)-362 (\336rst)-362 (lock)-363 (record)-363 (remains)]TJ
+ /N95 1 Tf
+ T*
+ (NULL)Tj
+ /N92 1 Tf
+ 2.4 0 TD
+ [(.)-258 (Unfortunately)65 (,)-259 (this)-258 (\322double-compare-and-sw)10 (ap\323)-258 (operation)-259 (is)-259 (not)-259 (supported)-258 (in)-259 (man)15 (y)-259 (archi-)]TJ
+ -2.4 -1.1667 TD
+ [(tectures)-266 (\(though)-265 (it)-266 (is)-265 (not)-265 (completely)-266 (unheard)-266 (of;)-265 (see)-265 ([10]\).)-266 (T)80 (o)-266 (get)-265 (around)-265 (this,)-265 (we)-266 (add)-265 (a)-266 (n)0 (e)25 (w)-265 (con-)]TJ
+ T*
+ [(straint)-322 (to)-322 (the)-322 (slo)25 (w)-322 (path.)-322 (W)80 (e)-323 (require)-322 (that)-322 (lock)-322 (records)-323 (be)-322 (allocated)-322 (with)-322 (eight-byte)-321 (alignment,)-322 (so)]TJ
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+ [(that)-229 (three)-229 (bits)-228 (are)-230 (zero)-229 (in)-229 (the)-230 (address)-228 (of)-229 (a)-228 (lock)-230 (record.)-228 (In)-229 (the)]TJ
+ /N95 1 Tf
+ 23.95 0 TD
+ (LOCKED)Tj
+ /N92 1 Tf
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+ -27.7792 -1.1667 TD
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+ T*
+ [(the)-307 (bit)-307 (is)-307 (0,)-307 (the)-307 (queue)-307 (\336eld)-307 (is)]TJ
+ /N95 1 Tf
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+ /N95 1 Tf
+ 15.7925 0 TD
+ (NULL)Tj
+ /N92 1 Tf
+ 2.4 0 TD
+ [(.)-307 (Thus,)-307 (the)-307 (\336rst)]TJ
+ -32.8 -1.1667 TD
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+ T*
+ [(meta-lock.)-247 (Once)-247 (this)-247 (in)40 (v)25 (ariant)-247 (may)-247 (be)-248 (assumed,)-247 (we)-247 (can)-248 (construct)-247 (an)-247 (e)15 (xtra)-247 (f)10 (ast)-247 (unlock)-247 (path:)-247 (check)]TJ
+ T*
+ [(the)-261 (locking)-262 (depth,)-261 (decrementing)-262 (it)-261 (and)-261 (returning)-262 (if)-261 (it)-261 (is)-261 (greater)-261 (than)-261 (one.)-262 (Otherwise,)-261 (construct)-262 (the)]TJ
+ T*
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+ [(clear)40 (,)]TJ
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+ (LOCKED)Tj
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+ [(state\),)-347 (and)-348 (the)-347 (desired)-348 (ne)25 (w)-347 (v)25 (alue)-347 (\(original)-347 (multi-use)-348 (bits,)]TJ
+ /N95 1 Tf
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+ (NEUTRAL)Tj
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+ -34.7925 -1.1667 TD
+ [(perform)-257 (a)]TJ
+ /N95 1 Tf
+ 4.1792 0 TD
+ (CAS)Tj
+ /N92 1 Tf
+ 2.0575 0 TD
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+ -6.2367 -1.1667 TD
+ [(no)-332 (other)-331 (thread)-332 (has)-331 (enqueued)-331 (a)-332 (lock)-331 (record,)-331 (then)-331 (the)]TJ
+ /N95 1 Tf
+ 21.9467 0 TD
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+ /N92 1 Tf
+ 2.1317 0 TD
+ [(succeeds)-331 (and)-332 (the)-331 (object)-331 (is)-331 (unlock)10 (ed;)]TJ
+ -24.0783 -1.1667 TD
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+ [(v)15 (ery)-231 (rare,)-231 (this)-232 (proposal)-231 (could)-231 (be)-231 (e)15 (xtended)-231 (to)-231 (also)-231 (summarize)-231 (the)-231 (lock)-231 (count)-231 (in)-231 (the)-231 (e)16 (xtra)-232 (bit,)-231 (so)-231 (that)]TJ
+ T*
+ [(a)-236 (zero)-236 (bit)-236 (observ)14 (ed)-236 (by)-236 (an)-235 (unlocking)-236 (thread)-236 (implied)-236 (both)-235 (a)]TJ
+ /N95 1 Tf
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+ (NULL)Tj
+ /N92 1 Tf
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+ [(queue)-236 (\336eld)-236 (and)-235 (a)-236 (lock)-236 (count)-235 (of)-236 (1,)]TJ
+ -25.7675 -1.1667 TD
+ 0 Tw
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+ 0 -1.75 TD
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+ 0 -1.1667 TD
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+ T*
+ [(unlocking,)-300 (b)20 (ut,)-299 (as)-299 (we)-300 (ha)20 (v)15 (e)-299 (discussed,)-299 (pays)-299 (for)-300 (that)-300 (lack)-300 (with)-299 (the)-300 (possibility)-299 (of)-299 (unbounded)-300 (b)20 (usy-)]TJ
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+ T*
+ (able.)Tj
+ /N91 1 Tf
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+ (6.3  Flexibility)Tj
+ /N92 1 Tf
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+ [(\337e)15 (xibility)-309 (results)-309 (from)-309 (the)-309 (f)10 (act)-309 (that)-309 (we)-309 (place)-309 (fe)25 (w)-310 (constraints)-308 (on)-309 (the)-310 (nature)-308 (of)-309 (the)-309 (data)-309 (structures)]TJ
+ T*
+ [(protected)-289 (by)-289 (the)-290 (meta-lock.)-288 (Speci\336cally)65 (,)-289 (i)0 (t)-289 (enables)-289 (separation)-289 (of)-289 (mechanism)-289 (and)-289 (polic)15 (y)65 (,)-289 (to)-289 (allo)25 (w)]TJ
+ T*
+ [(implementation of a v)26 (ariety of monitor semantics.)]TJ
+ 0 -1.75 TD
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+ 0 -1.1667 TD
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+ [(queues.)-232 (First,)-232 (consider)-233 (f)11 (airness.)-232 (Moti)25 (v)25 (ated)-232 (by)-232 (Buhr)]TJ
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+ -23 -1.1667 TD
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+ T*
+ [(ence)-263 (to)-262 (a)15 (w)9 (ak)11 (ened)-263 (w)9 (aiters)-262 (without)-262 (searching.)-263 (Similarly)65 (,)]TJ
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+ 22.3358 0 TD
+ (notify\(\))Tj
+ /N92 1 Tf
+ 5.0625 0 TD
+ [(can)-263 (e)15 (x)15 (ecute)-262 (in)-263 (constant)-262 (time,)]TJ
+ -27.3983 -1.1667 TD
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+ T*
+ [(tention.)-270 (T)79 (o)-271 (allo)25 (w)-270 (threads)-271 (to)-270 (append)-270 (lock)-271 (records)-270 (to)-271 (queues)-270 (without)-270 (ha)20 (ving)-271 (to)-270 (search)-271 (to)-270 (the)-271 (end)-270 (of)]TJ
+ T*
+ [(the)-272 (queue,)-273 (a)-272 (search)-273 (which)-272 (could)-272 (become)-272 (costly)-273 (if)-272 (queues)-272 (get)-272 (long,)-272 (we)-272 (k)10 (ept)-272 (head)-273 (and)-272 (tail)-272 (pointers)]TJ
+ T*
+ [(for)-367 (each)-367 (of)-368 (the)-367 (three)-367 (queues.)-368 (T)80 (ail)-367 (pointers)-367 (also)-367 (allo)25 (w)]TJ
+ /N95 1 Tf
+ 22.3133 0 TD
+ (notifyAll\(\))Tj
+ /N92 1 Tf
+ 6.9675 0 TD
+ [(to)-367 (run)-368 (in)-367 (constant)-367 (time,)]TJ
+ -29.2808 -1.1667 TD
+ [(re)15 (gardless)-305 (of)-304 (the)-305 (number)-305 (of)-304 (threads)-305 (w)10 (aiting,)-305 (via)-305 (list)-305 (concatenation.)-305 (While)-305 (this)-305 (alternati)26 (v)15 (e)-305 (imple-)]TJ
+ T*
+ [(mentation)-286 (w)9 (a)0 (s)-287 (straightforw)11 (ard,)-287 (performance)-287 (turned)-287 (out)-287 (to)-287 (be)-287 (inferior)-287 (to)-287 (our)-287 (single-queue)-286 (system)]TJ
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
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+ %%Page: 21 21
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+ PDFVars begin PDF begin PDFVars/InitAll get exec
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+ BT
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+ -19 56.4858 TD
+ [(because)-349 (greater)-349 (f)11 (airness)-350 (incurs)-348 (a)-349 (higher)-349 (conte)15 (xt)-349 (switch)-349 (rate)-349 (and)-348 (the)-350 (three-queue)-348 (data)-349 (structures)]TJ
+ 0 -1.1667 TD
+ 0 Tw
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+ /N91 1 Tf
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+ [(6.4  Hard)15 (war)18 (e without)]TJ
+ /N98 1 Tf
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+ /N91 1 Tf
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+ /N92 1 Tf
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+ [(The)-230 (meta-lock)-229 (algorithm)-230 (relies)-230 (on)-230 (tw)10 (o)-230 (\322)0 (e)16 (xotic\323)-230 (atomic)-230 (operations:)]TJ
+ /N95 1 Tf
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+ /N92 1 Tf
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+ /N95 1 Tf
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+ /N92 1 Tf
+ 1.8 0 TD
+ [(.)-230 (First,)-230 (note)-230 (that)]TJ
+ /N95 1 Tf
+ -32.7542 -1.1667 TD
+ (SWAP)Tj
+ /N92 1 Tf
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+ [(is)-248 (easily)-249 (simulated)-248 (using)]TJ
+ /N95 1 Tf
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+ /N92 1 Tf
+ 1.8 0 TD
+ [(:)-249 (repeatedly)-247 (read)-249 (the)-248 (memory)-248 (location)-249 (and)]TJ
+ /N95 1 Tf
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+ /N92 1 Tf
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+ -33.6683 -1.1667 TD
+ (The)Tj
+ /N95 1 Tf
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+ (CAS)Tj
+ /N92 1 Tf
+ 2.2142 0 TD
+ [(operation,)-414 (or)-414 (some)-414 (other)-414 (suf)25 (\336ciently)-413 (po)25 (werful)-414 (primiti)25 (v)15 (e)-414 (such)-414 (as)-414 (\322load-lock)10 (ed/store-)]TJ
+ -4.1833 -1.1667 TD
+ [(conditional,)70 (\323)-423 (seem)-422 (to)-423 (be)-422 (a)20 (v)25 (ailable)-423 (on)-422 (most)-422 (modern)-422 (architectures,)-422 (including)-422 (mainstream)-422 (Intel,)]TJ
+ T*
+ [(UltraSP)92 (ARC\252, Po)26 (werPC, and Alpha microprocessors.)]TJ
+ 0 -1.75 TD
+ [(The)-296 (JVM)-296 (in)-295 (which)-296 (we)-296 (implemented)-296 (our)-295 (synchronization)-296 (must)-296 (run)-295 (on)-296 (the)-296 (pre)25 (vious)-295 (generation)-295 (of)]TJ
+ 0 -1.1667 TD
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+ [(b)20 (u)0 (t)-314 (does)-314 (not)-314 (ha)20 (v)16 (e)]TJ
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+ /N92 1 Tf
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+ [(.)-314 (While)-314 (correctness)-313 (cannot)-314 (be)-314 (com-)]TJ
+ -24.5725 -1.1667 TD
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+ T*
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+ T*
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+ /N95 1 Tf
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+ /N92 1 Tf
+ 8.0633 0 TD
+ [(to)-263 (use)-264 (a)-263 (test-and-set)-263 (protocol)-263 (\(where)-263 (\322set\323)-263 (means)]TJ
+ -19.33 -1.1667 TD
+ [(sw)10 (apping)-311 (out)-311 (the)-311 (lock)10 (ed)-311 (v)25 (alue)-311 (1)-312 (and)-311 (\322test\323)-311 (means)-312 (obtaining)-311 (a)-311 (non-lock)10 (ed)-312 (v)25 (alue\).)-311 (When)-311 (the)-311 (test)]TJ
+ T*
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+ T*
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+ /N95 1 Tf
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+ /N92 1 Tf
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+ -14.4225 -1.1667 TD
+ [(course must be dif)25 (ferent from the lock)10 (ed v)25 (alue 1.)]TJ
+ /N91 1 Tf
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+ [(7  P)20 (erf)25 (ormance)]TJ
+ /N92 1 Tf
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+ T*
+ [(Since)-289 (dif)25 (ferent)-289 (systems)-289 (must)-288 (mak)10 (e)-289 (space/time)-288 (trade-of)25 (fs)-289 (dif)25 (ferently)65 (,)-289 (w)0 (e)-288 (shall)-289 (consider)-288 (space)-288 (and)]TJ
+ T*
+ [(time)-393 (costs)-393 (for)-392 (our)-393 (synchronization)-392 (algorithm)-393 (separately)66 (.)-393 (All)-393 (our)-393 (measurements)-393 (were)-393 (collected)]TJ
+ T*
+ [(using)-256 (a)-257 (near)20 (-FCS)-257 (v)15 (ersion)-257 (of)-256 (EVM)-257 (on)-257 (a)-256 (lightly)-257 (loaded)-256 (4-CPU)-257 (296)-257 (MHz)-257 (UltraSP)92 (ARC)-256 (system)-256 (with)]TJ
+ T*
+ [(2)-284 (gigabytes)-284 (of)-284 (RAM)-284 (and)-284 (the)-285 (Solaris\252)-284 (2.6)-284 (operating)-284 (system.)-283 (Some)-284 (measurements)-284 (were)-284 (obtained)]TJ
+ T*
+ [(by)-302 (adding)-300 (counters)-302 (to)-301 (the)-301 (code.)-301 (T)80 (o)-302 (minimize)-301 (the)-301 (disturbance)-301 (resulting)-301 (from)-301 (the)-301 (instrumentation,)]TJ
+ T*
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+ /N91 1 Tf
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+ (7.1  Benchmarks)Tj
+ /N92 1 Tf
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+ [(T)80 (able)-250 (1)-235 (sho)26 (ws)-235 (the)-234 (benchmarks)-234 (we)-234 (use)-234 (to)-234 (assess)-234 (the)-235 (performance)-234 (of)-234 (our)-234 (synchronization)-234 (code.)-234 (The)]TJ
+ T*
+ [(HelloW)80 (orld)-491 (program)-491 (sho)25 (ws)-491 (ho)25 (w)-490 (the)-490 (minimal)-491 (program)-491 (beha)21 (v)15 (es.)-491 (The)-490 (ne)15 (xt)-491 (se)26 (v)15 (e)0 (n)-491 (lines)-491 (sho)25 (w)]TJ
+ T*
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+ T*
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+ T*
+ [(The e)15 (x)15 (ecution times in the table are best of tw)11 (o runs.)]TJ
+ /N91 1 Tf
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+ [(7.2  Space perf)25 (ormance)]TJ
+ /N92 1 Tf
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+ [(W)80 (e)0 ( consider separately the space costs of)]TJ
+ /N94 1 Tf
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+ /N92 1 Tf
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+ ( and)Tj
+ /N94 1 Tf
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+ (unused)Tj
+ /N92 1 Tf
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+ [( synchronization capability)65 (.)]TJ
+ /N94 1 Tf
+ -23.3858 -1.75 TD
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+ /N92 1 Tf
+ 0 -1.1667 TD
+ [(From)-243 (the)-243 (description)-242 (of)-244 (our)-243 (algorithm,)-242 (it)-243 (follo)25 (ws)-243 (that)-242 (this)-243 (space)-243 (cost)-242 (is)-243 (proportional)-243 (to)-243 (the)-243 (number)]TJ
+ T*
+ [(of)-371 (lock)-371 (records)-370 (in)-371 (use)-371 (at)-371 (an)15 (y)-371 (point)-371 (in)-371 (time.)-371 (More)-371 (precisely)65 (,)-371 (since)-371 (threads)-371 (rec)15 (ycle)-371 (lock)-370 (records)]TJ
+ T*
+ [(locally)-240 (rather)-240 (than)-240 (globally)65 (,)-240 (w)0 (e)-240 (report)-240 (the)-240 (number)-240 (of)-239 (lock)-240 (records)-239 (allocated)-240 (by)-241 (the)-240 (global)-240 (allocator)]TJ
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
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+ BT
+ /N92 1 Tf
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+ 0 g
+ 0 Tc
+ (19)Tj
+ -19 20.0692 TD
+ [(during)-334 (the)-334 (e)15 (x)15 (ecution)-334 (of)-334 (each)-335 (benchmark.)-333 (This)-334 (higher)-334 (number)-334 (re\337ects)-334 (our)-334 (implementation)-334 (more)]TJ
+ 0 -1.1667 TD
+ [(accurately)65 (.)-314 (I)0 (n)-314 (the)-315 (w)10 (orst)-315 (case,)-314 (a)-315 (program)-314 (will)-314 (synchronize)-314 (on)-314 (e)25 (v)15 (ery)-315 (object)-314 (allocated)-315 (\(see)-314 (Section)]TJ
+ T*
+ [(2.2\),)-252 (making)-252 (the)-252 (w)10 (orst-case)-252 (space)-252 (cost)-251 (of)-252 (our)-252 (algorithm,)-252 (as)-252 (well)-251 (as)-252 (of)-252 (an)15 (y)-252 (other)-252 (algorithm)-252 (that)-252 (we)]TJ
+ T*
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+ T*
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+ T*
+ [(lock)-225 (records)-225 (allocated)-225 (is)-225 (v)15 (ery)-225 (small,)-225 (and)-225 (pales)-225 (in)-225 (comparison)-225 (with)-225 (the)-225 (total)-225 (number)-226 (of)-224 (objects)-225 (allo-)]TJ
+ T*
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+ T*
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+ /N94 1 Tf
+ 0 -1.75 TD
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+ /N92 1 Tf
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+ T*
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+ /N94 1 Tf
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+ /N92 1 Tf
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+ -19.2867 -1.1667 TD
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+ T*
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+ /N91 1 Tf
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+ -38.926 -2.9 TD
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+ (a)Tj
+ 10 0 0 10 415.81 658.33 Tm
+ [(#thr)18 (eads)]TJ
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+ -0.943 -1.2 TD
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+ 4.314 1.2 TD
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+ -0.249 -1.2 TD
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+ /N92 1 Tf
+ -42.822 -1.7 TD
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+ T*
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+ T*
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+ T*
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+ -41.197 -0.85 TD
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+ 0 -1.7 TD
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+ 0 -1.5 TD
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+ 1.079 -1.2 TD
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+ T*
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+ -6 -1.1667 TD
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+ [(without extra fast)-10388 (with extra fast)]TJ
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+ [(Benchmark)-3832 (# getMetaLock)-1246 (#getMetaLockSlo)10 (w)-1246 (#)0 ( getMetaLock)-1375 (#getMetaLockSlo)10 (w)]TJ
+ /N92 1 Tf
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+ [(Hello)-11647 (3,054)-8059 (0)-6309 (1,418)-8317 (0)]TJ
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+ T*
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+ T*
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+ T*
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+ T*
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+ T*
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+ 0 -1.1667 TD
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+ 0 -1.1667 TD
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+ /N94 1 Tf
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+ /N92 1 Tf
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+ -10.4842 -1.1667 TD
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+ T*
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+ T*
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+ T*
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+ /N92 1 Tf
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+ T*
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+ T*
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+ /N95 1 Tf
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+ (! getMetaLock)Tj
+ 0 -1.25 TD
+ (or      %i0, 3, %l0             ! %l0 = my busy value)Tj
+ T*
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+ T*
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+ T*
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+ T*
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+ (beq     slowGetMetaLockPath)Tj
+ T*
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+ 19.2 -1.25 TD
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+ T*
+ (! and synch operation gets lock)Tj
+ T*
+ (! record pointer or age&hash in %l0)Tj
+ -19.2 -1.25 TD
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+ T*
+ (! releaseMetaLock)Tj
+ T*
+ (or      %i0, 3, %l0             ! %l0 = my busy value)Tj
+ T*
+ (cas     [%l1], %l0, %l2         ! if [%l1] == %l0 then swap\([%l0],%l2\)\
+ )Tj
+ T*
+ (cmp     %l0, %l2                ! did we do the swap?)Tj
+ T*
+ (bne     slowReleaseMetaLockPath)Tj
+ T*
+ (! unfilled delay slot here)Tj
+ ET
+ PDFVars/TermAll get exec end end
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+ showpage
+ %%PageTrailer
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+ -19 56.4858 TD
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+ 0 -1.1667 TD
+ [(release)-454 (an)-454 (uncontended)-454 (meta-lock.)-454 (Each)-454 (of)-454 (those)-454 (paths)-454 (includes)-454 (a)-454 (single)-454 (atomic)-454 (instruction.)]TJ
+ T*
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+ [(b)20 (usy-w)10 (aiting, and only v)15 (ery rarely allocates from global memory)66 (.)]TJ
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+ T*
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+ 0 -1.75 TD
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+ 0 -1.1667 TD
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+ T*
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+ T*
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+ T*
+ [(Synthetic)-366 (benchmarks)-366 (designed)-366 (to)-366 (isolate)-366 (the)-366 (cost)-366 (of)-366 (synchronization)-366 (indicate)-366 (that)-366 (our)-366 (scheme)]TJ
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+ [(time services in a Ja)20 (v)25 (a)0 ( VM may be safely implemented using the Ja)22 (v)25 (a)0 ( programming language.)]TJ
+ 0 -1.9167 TD
+ [(Ross)-247 (Knippel)-247 (is)-247 (a)-247 (Senior)-247 (Staf)25 (f)-247 (Engineer)-247 (in)-247 (the)-247 (Ja)20 (v)25 (a)-247 (T)69 (echnology)-246 (Group)-247 (of)-247 (Solaris)-247 (Softw)10 (are.)-247 (Pre)25 (vi-)]TJ
+ 0 -1.1667 TD
+ [(ously)65 (,)-284 (h)0 (e)-284 (w)10 (ork)10 (ed)-283 (at)-285 (both)-284 (Cray)-284 (Research)-283 (and)-284 (Cray)-284 (Computer)40 (,)-283 (d)0 (e)25 (v)15 (eloping)-284 (compilers)-284 (for)-284 (the)-284 (XMP)111 (,)]TJ
+ T*
+ [(Cray3, and Cray4. He has a B.S. de)16 (gree in Computer Science from the Uni)26 (v)15 (ersity of Minnesota.)]TJ
+ 0 -1.9167 TD
+ [(Y)129 (.S.)-259 (Ramakrishna)-259 (is)-260 (a)-260 (Staf)25 (f)-259 (Engineer)-260 (with)-259 (the)-260 (Ja)21 (v)25 (a)-260 (T)70 (echnology)-260 (Group)-259 (at)-260 (Sun)-260 (Microsystems.)-259 (Pre-)]TJ
+ 0 -1.1667 TD
+ [(viously)65 (,)-302 (h)0 (e)-301 (w)10 (ork)11 (ed)-302 (at)-301 (TIFR,)-301 (Bombay)65 (,)-302 (and)-302 (at)-301 (SUNY)130 (,)-302 (Ston)15 (y)-302 (Brook,)-302 (on)-301 (the)-302 (use)-301 (of)-301 (temporal)-301 (logics)]TJ
+ T*
+ [(and)-228 (model-checking)-227 (for)-228 (the)-228 (v)15 (eri\336cation)-227 (of)-228 (concurrent)-228 (systems.)-228 (He)-227 (has)-228 (a)-228 (B.T)70 (ech.)-228 (from)-228 (IIT)-228 (Kanpur)40 (,)]TJ
+ T*
+ (and an M.S. and Ph.D. from UC Santa Barbara.)Tj
+ 0 -1.9167 TD
+ [(Derek)-262 (White)-262 (is)-261 (a)-262 (Staf)25 (f)-262 (Engineer)-261 (at)-262 (Sun)-261 (Microsystems)-261 (Laboratories)-262 (in)-262 (Burlington,)-262 (Massachusetts.)]TJ
+ 0 -1.1667 TD
+ [(He)-329 (is)-329 (a)-328 (member)-329 (of)-329 (the)-329 (Ja)21 (v)25 (a)-329 (T)80 (opics)-329 (Group,)-329 (which)-328 (has)-329 (de)25 (v)15 (eloped)-329 (a)-328 (JVM)-329 (as)-329 (an)-329 (infrastructure)-329 (for)]TJ
+ T*
+ [(de)25 (v)15 (eloping)-347 (soft)-347 (real-time)-347 (and)-348 (scalable)-347 (garbage)-347 (collection)-347 (for)-347 (the)-347 (Ja)20 (v)26 (a)-348 (language.)-347 (The)-347 (group)-347 (has)]TJ
+ T*
+ [(also)-229 (studied)-229 (and)-229 (optimized)-230 (JVM)-229 (performance)-228 (as)-229 (a)-229 (whole.)-229 (Other)-230 (interests)-228 (include)-229 (performance)-229 (and)]TJ
+ T*
+ [(heap)-444 (analysis)-444 (tools,)-444 (and)-444 (incremental)-445 (de)26 (v)15 (elopment)-444 (en)40 (vironments.)-444 (Prior)-445 (to)-444 (joining)-444 (Sun,)-444 (Derek)]TJ
+ T*
+ [(w)10 (ork)10 (ed)-301 (for)-301 (eight)-301 (years)-300 (at)-301 (Apple)-301 (Computer)40 (,)-300 (Inc.,)-301 (where)-300 (he)-301 (w)10 (a)0 (s)-301 (responsible)-301 (for)-301 (the)-300 (Object)-301 (P)15 (ascal)]TJ
+ T*
+ [(compiler)-388 (and)-388 (w)10 (ork)10 (ed)-388 (on)-388 (the)-389 (Dylan)-388 (programming)-388 (language)-388 (runtime)-388 (and)-388 (de)25 (v)15 (elopment)-388 (en)40 (viron-)]TJ
+ T*
+ (ment.)Tj
+ ET
+ PDFVars/TermAll get exec end end
+ userdict /pgsave get restore
+ showpage
+ %%PageTrailer
+ %%EndPage
+ %%Trailer
+ %%EOF


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CVSTrac 2.0.1