ossp-pkg/pth/pth_uctx.c
1.7
/*
** GNU Pth - The GNU Portable Threads
** Copyright (c) 1999-2007 Ralf S. Engelschall <rse@engelschall.com>
**
** This file is part of GNU Pth, a non-preemptive thread scheduling
** library which can be found at http://www.gnu.org/software/pth/.
**
** This library is free software; you can redistribute it and/or
** modify it under the terms of the GNU Lesser General Public
** License as published by the Free Software Foundation; either
** version 2.1 of the License, or (at your option) any later version.
**
** This library is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
** Lesser General Public License for more details.
**
** You should have received a copy of the GNU Lesser General Public
** License along with this library; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
** USA, or contact Ralf S. Engelschall <rse@engelschall.com>.
**
** pth_uctx.c: Pth user-space context handling (stand-alone sub-API)
*/
/* ``It worries me however, to realize
how tough an ass-hole I have had to
be, in order to get to stick to the
principle of doing things right,
rather than "just hack it in".''
-- Poul-Henning Kamp <phk@FreeBSD.org> */
#include "pth_p.h"
/* user-space context structure */
struct pth_uctx_st {
int uc_stack_own; /* whether stack were allocated by us */
char *uc_stack_ptr; /* pointer to start address of stack area */
size_t uc_stack_len; /* size of stack area */
int uc_mctx_set; /* whether uc_mctx is set */
pth_mctx_t uc_mctx; /* saved underlying machine context */
};
/* create user-space context structure */
int
pth_uctx_create(
pth_uctx_t *puctx)
{
pth_uctx_t uctx;
/* argument sanity checking */
if (puctx == NULL)
return pth_error(FALSE, EINVAL);
/* allocate the context structure */
if ((uctx = (pth_uctx_t)malloc(sizeof(struct pth_uctx_st))) == NULL)
return pth_error(FALSE, errno);
/* initialize the context structure */
uctx->uc_stack_own = FALSE;
uctx->uc_stack_ptr = NULL;
uctx->uc_stack_len = 0;
uctx->uc_mctx_set = FALSE;
memset((void *)&uctx->uc_mctx, 0, sizeof(pth_mctx_t));
/* pass result to caller */
*puctx = uctx;
return TRUE;
}
/* trampoline context */
typedef struct {
pth_mctx_t *mctx_parent;
pth_uctx_t uctx_this;
pth_uctx_t uctx_after;
void (*start_func)(void *);
void *start_arg;
} pth_uctx_trampoline_t;
pth_uctx_trampoline_t pth_uctx_trampoline_ctx;
/* trampoline function for pth_uctx_make() */
static void pth_uctx_trampoline(void)
{
volatile pth_uctx_trampoline_t ctx;
/* move context information from global to local storage */
ctx.mctx_parent = pth_uctx_trampoline_ctx.mctx_parent;
ctx.uctx_this = pth_uctx_trampoline_ctx.uctx_this;
ctx.uctx_after = pth_uctx_trampoline_ctx.uctx_after;
ctx.start_func = pth_uctx_trampoline_ctx.start_func;
ctx.start_arg = pth_uctx_trampoline_ctx.start_arg;
/* switch back to parent */
pth_mctx_switch(&(ctx.uctx_this->uc_mctx), ctx.mctx_parent);
/* enter start function */
(*ctx.start_func)(ctx.start_arg);
/* switch to successor user-space context */
if (ctx.uctx_after != NULL)
pth_mctx_restore(&(ctx.uctx_after->uc_mctx));
/* terminate process (the only reasonable thing to do here) */
exit(0);
/* NOTREACHED */
return;
}
/* make setup of user-space context structure */
int
pth_uctx_make(
pth_uctx_t uctx,
char *sk_addr, size_t sk_size,
const sigset_t *sigmask,
void (*start_func)(void *), void *start_arg,
pth_uctx_t uctx_after)
{
pth_mctx_t mctx_parent;
sigset_t ss;
/* argument sanity checking */
if (uctx == NULL || start_func == NULL || sk_size < 16*1024)
return pth_error(FALSE, EINVAL);
/* configure run-time stack */
if (sk_addr == NULL) {
if ((sk_addr = (char *)malloc(sk_size)) == NULL)
return pth_error(FALSE, errno);
uctx->uc_stack_own = TRUE;
}
else
uctx->uc_stack_own = FALSE;
uctx->uc_stack_ptr = sk_addr;
uctx->uc_stack_len = sk_size;
/* configure the underlying machine context */
if (!pth_mctx_set(&uctx->uc_mctx, pth_uctx_trampoline,
uctx->uc_stack_ptr, uctx->uc_stack_ptr+uctx->uc_stack_len))
return pth_error(FALSE, errno);
/* move context information into global storage for the trampoline jump */
pth_uctx_trampoline_ctx.mctx_parent = &mctx_parent;
pth_uctx_trampoline_ctx.uctx_this = uctx;
pth_uctx_trampoline_ctx.uctx_after = uctx_after;
pth_uctx_trampoline_ctx.start_func = start_func;
pth_uctx_trampoline_ctx.start_arg = start_arg;
/* optionally establish temporary signal mask */
if (sigmask != NULL)
sigprocmask(SIG_SETMASK, sigmask, &ss);
/* perform the trampoline step */
pth_mctx_switch(&mctx_parent, &(uctx->uc_mctx));
/* optionally restore original signal mask */
if (sigmask != NULL)
sigprocmask(SIG_SETMASK, &ss, NULL);
/* finally flag that the context is now configured */
uctx->uc_mctx_set = TRUE;
return TRUE;
}
/* switch from current to other user-space context */
int
pth_uctx_switch(
pth_uctx_t uctx_from,
pth_uctx_t uctx_to)
{
/* argument sanity checking */
if (uctx_from == NULL || uctx_to == NULL)
return pth_error(FALSE, EINVAL);
if (!(uctx_to->uc_mctx_set))
return pth_error(FALSE, EPERM);
/* switch underlying machine context */
uctx_from->uc_mctx_set = TRUE;
pth_mctx_switch(&(uctx_from->uc_mctx), &(uctx_to->uc_mctx));
return TRUE;
}
/* destroy user-space context structure */
int
pth_uctx_destroy(
pth_uctx_t uctx)
{
/* argument sanity checking */
if (uctx == NULL)
return pth_error(FALSE, EINVAL);
/* deallocate dynamically allocated stack */
if (uctx->uc_stack_own && uctx->uc_stack_ptr != NULL)
free(uctx->uc_stack_ptr);
/* deallocate context structure */
free(uctx);
return TRUE;
}
