SDL_sysmutex.c
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/*
Simple DirectMedia Layer
Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org>
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
*/
#include "SDL_config.h"
/* An implementation of mutexes using semaphores */
#include "SDL_thread.h"
#include "SDL_systhread_c.h"
struct SDL_mutex
{
int recursive;
SDL_threadID owner;
SDL_sem *sem;
};
/* Create a mutex */
SDL_mutex *
SDL_CreateMutex(void)
{
SDL_mutex *mutex;
/* Allocate mutex memory */
mutex = (SDL_mutex *) SDL_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) {
SDL_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);
}
SDL_free(mutex);
}
}
/* Lock the semaphore */
int
SDL_mutexP(SDL_mutex * mutex)
{
#if SDL_THREADS_DISABLED
return 0;
#else
SDL_threadID this_thread;
if (mutex == NULL) {
return SDL_SetError("Passed a NULL mutex");
}
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 /* SDL_THREADS_DISABLED */
}
/* Unlock the mutex */
int
SDL_mutexV(SDL_mutex * mutex)
{
#if SDL_THREADS_DISABLED
return 0;
#else
if (mutex == NULL) {
return SDL_SetError("Passed a NULL mutex");
}
/* If we don't own the mutex, we can't unlock it */
if (SDL_ThreadID() != mutex->owner) {
return SDL_SetError("mutex not owned by this thread");
}
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 /* SDL_THREADS_DISABLED */
}
/* vi: set ts=4 sw=4 expandtab: */