/*

    SDL - Simple DirectMedia Layer

    Copyright (C) 1997-2006 Sam Lantinga

    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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga

    slouken@libsdl.org

*/

#include "SDL_config.h"

/* An implementation of mutexes using semaphores */

#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 */

	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

	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 /* SDL_THREADS_DISABLED */

}

/* Unlock the mutex */

int SDL_mutexV(SDL_mutex *mutex)

{

#if SDL_THREADS_DISABLED

	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 /* SDL_THREADS_DISABLED */

}