SDL_sysmutex.c
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/*
SDL - Simple DirectMedia Layer
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Copyright (C) 1997-2006 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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*/
/* An implementation of mutexes using semaphores */
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#include "SDL_stdlib.h"
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#include "SDL_error.h"
#include "SDL_thread.h"
#include "SDL_systhread_c.h"
struct SDL_mutex {
int recursive;
Uint32 owner;
SDL_sem *sem;
};
/* Create a mutex */
SDL_mutex *SDL_CreateMutex(void)
{
SDL_mutex *mutex;
/* Allocate mutex memory */
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mutex = (SDL_mutex *)SDL_malloc(sizeof(*mutex));
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if ( mutex ) {
/* Create the mutex semaphore, with initial value 1 */
mutex->sem = SDL_CreateSemaphore(1);
mutex->recursive = 0;
mutex->owner = 0;
if ( ! mutex->sem ) {
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SDL_free(mutex);
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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);
}
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SDL_free(mutex);
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}
}
/* Lock the semaphore */
int SDL_mutexP(SDL_mutex *mutex)
{
#ifdef DISABLE_THREADS
return 0;
#else
Uint32 this_thread;
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 */
}