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SDL_sysmutex.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,
but WITHOUT ANY WARRANTY; without even the implied warranty of
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
License along with this library; if not, write to the Free Software
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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*/
#ifdef SAVE_RCSID
static char rcsid =
"@(#) $Id: SDL_sysmutex.c,v 1.2 2001/04/26 16:50:18 hercules Exp $";
#endif
/* An implementation of mutexes using semaphores */
#include <stdio.h>
#include <stdlib.h>
#include "SDL_error.h"
#include "SDL_thread.h"
#include "SDL_systhread_c.h"
struct SDL_mutex
{
int recursive;
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SDL_threadID owner;
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SDL_sem *sem;
};
/* Create a mutex */
SDL_mutex *
SDL_CreateMutex(void)
{
SDL_mutex *mutex;
/* Allocate mutex memory */
mutex = (SDL_mutex *) malloc(sizeof(*mutex));
if (mutex) {
/* Create the mutex semaphore, with initial value 1 */
mutex->sem = SDL_CreateSemaphore(1);
mutex->recursive = 0;
mutex->owner = 0;
if (!mutex->sem) {
free(mutex);
mutex = NULL;
}
} else {
SDL_OutOfMemory();
}
return mutex;
}
/* Free the mutex */
void
SDL_DestroyMutex(SDL_mutex * mutex)
{
if (mutex) {
if (mutex->sem) {
SDL_DestroySemaphore(mutex->sem);
}
free(mutex);
}
}
/* Lock the semaphore */
int
SDL_mutexP(SDL_mutex * mutex)
{
#ifdef DISABLE_THREADS
return 0;
#else
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SDL_threadID this_thread;
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if (mutex == NULL) {
SDL_SetError("Passed a NULL mutex");
return -1;
}
this_thread = SDL_ThreadID();
if (mutex->owner == this_thread) {
++mutex->recursive;
} else {
/* The order of operations is important.
We set the locking thread id after we obtain the lock
so unlocks from other threads will fail.
*/
SDL_SemWait(mutex->sem);
mutex->owner = this_thread;
mutex->recursive = 0;
}
return 0;
#endif /* DISABLE_THREADS */
}
/* Unlock the mutex */
int
SDL_mutexV(SDL_mutex * mutex)
{
#ifdef DISABLE_THREADS
return 0;
#else
if (mutex == NULL) {
SDL_SetError("Passed a NULL mutex");
return -1;
}
/* If we don't own the mutex, we can't unlock it */
if (SDL_ThreadID() != mutex->owner) {
SDL_SetError("mutex not owned by this thread");
return -1;
}
if (mutex->recursive) {
--mutex->recursive;
} else {
/* The order of operations is important.
First reset the owner so another thread doesn't lock
the mutex and set the ownership before we reset it,
then release the lock semaphore.
*/
mutex->owner = 0;
SDL_SemPost(mutex->sem);
}
return 0;
#endif /* DISABLE_THREADS */
}