144 lines
3.4 KiB
C
144 lines
3.4 KiB
C
/*
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SDL - Simple DirectMedia Layer
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Copyright (C) 1997-2011 Sam Lantinga
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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Sam Lantinga
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slouken@libsdl.org
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*/
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#ifdef SAVE_RCSID
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static char rcsid =
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"@(#) $Id: SDL_sysmutex.c,v 1.2 2001/04/26 16:50:18 hercules Exp $";
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#endif
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/* An implementation of mutexes using semaphores */
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#include <stdio.h>
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#include <stdlib.h>
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#include "SDL_error.h"
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#include "SDL_thread.h"
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#include "SDL_systhread_c.h"
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struct SDL_mutex
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{
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int recursive;
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SDL_threadID owner;
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SDL_sem *sem;
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};
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/* Create a mutex */
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SDL_mutex *
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SDL_CreateMutex(void)
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{
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SDL_mutex *mutex;
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/* Allocate mutex memory */
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mutex = (SDL_mutex *) malloc(sizeof(*mutex));
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if (mutex) {
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/* Create the mutex semaphore, with initial value 1 */
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mutex->sem = SDL_CreateSemaphore(1);
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mutex->recursive = 0;
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mutex->owner = 0;
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if (!mutex->sem) {
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free(mutex);
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mutex = NULL;
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}
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} else {
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SDL_OutOfMemory();
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}
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return mutex;
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}
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/* Free the mutex */
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void
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SDL_DestroyMutex(SDL_mutex * mutex)
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{
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if (mutex) {
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if (mutex->sem) {
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SDL_DestroySemaphore(mutex->sem);
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}
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free(mutex);
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}
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}
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/* Lock the semaphore */
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int
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SDL_mutexP(SDL_mutex * mutex)
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{
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#ifdef DISABLE_THREADS
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return 0;
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#else
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SDL_threadID this_thread;
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if (mutex == NULL) {
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SDL_SetError("Passed a NULL mutex");
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return -1;
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}
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this_thread = SDL_ThreadID();
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if (mutex->owner == this_thread) {
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++mutex->recursive;
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} else {
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/* The order of operations is important.
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We set the locking thread id after we obtain the lock
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so unlocks from other threads will fail.
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*/
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SDL_SemWait(mutex->sem);
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mutex->owner = this_thread;
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mutex->recursive = 0;
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}
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return 0;
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#endif /* DISABLE_THREADS */
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}
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/* Unlock the mutex */
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int
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SDL_mutexV(SDL_mutex * mutex)
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{
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#ifdef DISABLE_THREADS
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return 0;
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#else
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if (mutex == NULL) {
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SDL_SetError("Passed a NULL mutex");
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return -1;
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}
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/* If we don't own the mutex, we can't unlock it */
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if (SDL_ThreadID() != mutex->owner) {
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SDL_SetError("mutex not owned by this thread");
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return -1;
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}
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if (mutex->recursive) {
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--mutex->recursive;
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} else {
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/* The order of operations is important.
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First reset the owner so another thread doesn't lock
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the mutex and set the ownership before we reset it,
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then release the lock semaphore.
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*/
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mutex->owner = 0;
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SDL_SemPost(mutex->sem);
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}
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return 0;
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#endif /* DISABLE_THREADS */
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}
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/* vi: set ts=4 sw=4 expandtab: */
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