ossp-pkg/pth/pth_ring.c
/*
** 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_ring.c: Pth ring data structure
*/
/* ``Unix was not designed to stop people
from doing stupid things, because that
would also stop them from doing clever
things.'' --Doug Gwyn */
/*
* This is a "ring" data structure, a special case of a list. It is
* implemented through double-chained nodes. The link structure is part
* of the nodes, i.e. no extra memory is required for the ring itself
* and the ring can contain as many nodes as fit into memory. The main
* advantage of using a ring instead of a plain list is to make the ring
* operations easier (less special cases!). The ring is usually used
* in Pth to represent a "set" of something. All operations are O(1),
* except for the check whether a node is part of the ring (which is
* O(N)).
*/
#include "pth_p.h"
/* initialize ring; O(1) */
intern void pth_ring_init(pth_ring_t *r)
{
if (r == NULL)
return;
r->r_hook = NULL;
r->r_nodes = 0;
return;
}
/* return number of nodes in ring; O(1) */
#if cpp
#define pth_ring_elements(r) \
((r) == NULL ? (-1) : (r)->r_nodes)
#endif
/* return first node in ring; O(1) */
#if cpp
#define pth_ring_first(r) \
((r) == NULL ? NULL : (r)->r_hook)
#endif
/* return last node in ring; O(1) */
#if cpp
#define pth_ring_last(r) \
((r) == NULL ? NULL : ((r)->r_hook == NULL ? NULL : (r)->r_hook->rn_prev))
#endif
/* walk to next node in ring; O(1) */
#if cpp
#define pth_ring_next(r, rn) \
(((r) == NULL || (rn) == NULL) ? NULL : ((rn)->rn_next == (r)->r_hook ? NULL : (rn)->rn_next))
#endif
/* walk to previous node in ring; O(1) */
#if cpp
#define pth_ring_prev(r, rn) \
(((r) == NULL || (rn) == NULL) ? NULL : ((rn)->rn_prev == (r)->r_hook->rn_prev ? NULL : (rn)->rn_prev))
#endif
/* insert node into ring; O(1) */
#if cpp
#define pth_ring_insert(r, rn) \
pth_ring_append((r), (rn))
#endif
/* insert node after a second node in ring; O(1) */
intern void pth_ring_insert_after(pth_ring_t *r, pth_ringnode_t *rn1, pth_ringnode_t *rn2)
{
if (r == NULL || rn1 == NULL || rn2 == NULL)
return;
rn2->rn_prev = rn1;
rn2->rn_next = rn1->rn_next;
rn2->rn_prev->rn_next = rn2;
rn2->rn_next->rn_prev = rn2;
r->r_nodes++;
return;
}
/* insert node before a second node in ring; O(1) */
intern void pth_ring_insert_before(pth_ring_t *r, pth_ringnode_t *rn1, pth_ringnode_t *rn2)
{
if (r == NULL || rn1 == NULL || rn2 == NULL)
return;
rn2->rn_next = rn1;
rn2->rn_prev = rn1->rn_prev;
rn2->rn_prev->rn_next = rn2;
rn2->rn_next->rn_prev = rn2;
r->r_nodes++;
return;
}
/* delete an node from ring; O(1) */
intern void pth_ring_delete(pth_ring_t *r, pth_ringnode_t *rn)
{
if (r == NULL || rn == NULL)
return;
if (r->r_hook == rn && rn->rn_prev == rn && rn->rn_next == rn)
r->r_hook = NULL;
else {
if (r->r_hook == rn)
r->r_hook = rn->rn_next;
rn->rn_prev->rn_next = rn->rn_next;
rn->rn_next->rn_prev = rn->rn_prev;
}
r->r_nodes--;
return;
}
/* prepend an node to ring; O(1) */
intern void pth_ring_prepend(pth_ring_t *r, pth_ringnode_t *rn)
{
if (r == NULL || rn == NULL)
return;
if (r->r_hook == NULL) {
r->r_hook = rn;
rn->rn_next = rn;
rn->rn_prev = rn;
}
else {
rn->rn_next = r->r_hook;
rn->rn_prev = r->r_hook->rn_prev;
rn->rn_next->rn_prev = rn;
rn->rn_prev->rn_next = rn;
r->r_hook = rn;
}
r->r_nodes++;
return;
}
/* append an node to ring; O(1) */
intern void pth_ring_append(pth_ring_t *r, pth_ringnode_t *rn)
{
if (r == NULL || rn == NULL)
return;
if (r->r_hook == NULL) {
r->r_hook = rn;
rn->rn_next = rn;
rn->rn_prev = rn;
}
else {
rn->rn_next = r->r_hook;
rn->rn_prev = r->r_hook->rn_prev;
rn->rn_next->rn_prev = rn;
rn->rn_prev->rn_next = rn;
}
r->r_nodes++;
return;
}
/* treat ring as stack: push node onto stack; O(1) */
#if cpp
#define pth_ring_push(r, rn) \
pth_ring_prepend((r), (rn))
#endif
/* treat ring as stack: pop node from stack; O(1) */
intern pth_ringnode_t *pth_ring_pop(pth_ring_t *r)
{
pth_ringnode_t *rn;
rn = pth_ring_first(r);
if (rn != NULL)
pth_ring_delete(r, rn);
return rn;
}
/* treat ring as queue: favorite a node in the ring; O(1) */
intern int pth_ring_favorite(pth_ring_t *r, pth_ringnode_t *rn)
{
if (r == NULL)
return FALSE;
if (r->r_hook == NULL)
return FALSE;
/* element is perhaps already at ring hook */
if (r->r_hook == rn)
return TRUE;
/* move to hook of ring */
pth_ring_delete(r, rn);
pth_ring_prepend(r, rn);
return TRUE;
}
/* treat ring as queue: enqueue node; O(1) */
#if cpp
#define pth_ring_enqueue(r, rn) \
pth_ring_prepend((r), (rn))
#endif
/* treat ring as queue: dequeue node; O(1) */
intern pth_ringnode_t *pth_ring_dequeue(pth_ring_t *r)
{
pth_ringnode_t *rn;
rn = pth_ring_last(r);
if (rn != NULL)
pth_ring_delete(r, rn);
return rn;
}
/* check whether node is contained in ring; O(n) */
intern int pth_ring_contains(pth_ring_t *r, pth_ringnode_t *rns)
{
pth_ringnode_t *rn;
int rc;
if (r == NULL || rns == NULL)
return pth_error(FALSE, EINVAL);
rc = FALSE;
rn = r->r_hook;
if (rn != NULL) {
do {
if (rn == rns) {
rc = TRUE;
break;
}
rn = rn->rn_next;
} while (rn != r->r_hook);
}
return rc;
}
