/*

    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 semaphores using mutexes and condition variables */

#include "SDL_timer.h"

#include "SDL_thread.h"

#include "SDL_systhread_c.h"

#if SDL_THREADS_DISABLED

SDL_sem *SDL_CreateSemaphore(Uint32 initial_value)

{

	SDL_SetError("SDL not configured with thread support");

	return (SDL_sem *)0;

}

void SDL_DestroySemaphore(SDL_sem *sem)

{

	return;

}

int SDL_SemTryWait(SDL_sem *sem)

{

	SDL_SetError("SDL not configured with thread support");

	return -1;

}

int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)

{

	SDL_SetError("SDL not configured with thread support");

	return -1;

}

int SDL_SemWait(SDL_sem *sem)

{

	SDL_SetError("SDL not configured with thread support");

	return -1;

}

Uint32 SDL_SemValue(SDL_sem *sem)

{

	return 0;

}

int SDL_SemPost(SDL_sem *sem)

{

	SDL_SetError("SDL not configured with thread support");

	return -1;

}

#else

struct SDL_semaphore

{

	Uint32 count;

	Uint32 waiters_count;

	SDL_mutex *count_lock;

	SDL_cond *count_nonzero;

};

SDL_sem *SDL_CreateSemaphore(Uint32 initial_value)

{

	SDL_sem *sem;

	sem = (SDL_sem *)SDL_malloc(sizeof(*sem));

	if ( ! sem ) {

		SDL_OutOfMemory();

		return NULL;

	}

	sem->count = initial_value;

	sem->waiters_count = 0;

	sem->count_lock = SDL_CreateMutex();

	sem->count_nonzero = SDL_CreateCond();

	if ( ! sem->count_lock || ! sem->count_nonzero ) {

		SDL_DestroySemaphore(sem);

		return NULL;

	}

	return sem;

}

/* WARNING:

   You cannot call this function when another thread is using the semaphore.

*/

void SDL_DestroySemaphore(SDL_sem *sem)

{

	if ( sem ) {

		sem->count = 0xFFFFFFFF;

		while ( sem->waiters_count > 0) {

			SDL_CondSignal(sem->count_nonzero);

			SDL_Delay(10);

		}

		SDL_DestroyCond(sem->count_nonzero);

		if ( sem->count_lock ) {

			SDL_mutexP(sem->count_lock);

			SDL_mutexV(sem->count_lock);

			SDL_DestroyMutex(sem->count_lock);

		}

		SDL_free(sem);

	}

}

int SDL_SemTryWait(SDL_sem *sem)

{

	int retval;

	if ( ! sem ) {

		SDL_SetError("Passed a NULL semaphore");

		return -1;

	}

	retval = SDL_MUTEX_TIMEDOUT;

	SDL_LockMutex(sem->count_lock);

	if ( sem->count > 0 ) {

		--sem->count;

		retval = 0;

	}

	SDL_UnlockMutex(sem->count_lock);

	return retval;

}

int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)

{

	int retval;

	if ( ! sem ) {

		SDL_SetError("Passed a NULL semaphore");

		return -1;

	}

	/* A timeout of 0 is an easy case */

	if ( timeout == 0 ) {

		return SDL_SemTryWait(sem);

	}

	SDL_LockMutex(sem->count_lock);

	++sem->waiters_count;

	retval = 0;

	while ( (sem->count == 0) && (retval != SDL_MUTEX_TIMEDOUT) ) {

		retval = SDL_CondWaitTimeout(sem->count_nonzero,

		                             sem->count_lock, timeout);

	}

	--sem->waiters_count;

	--sem->count;

	SDL_UnlockMutex(sem->count_lock);

	return retval;

}

int SDL_SemWait(SDL_sem *sem)

{

	return SDL_SemWaitTimeout(sem, SDL_MUTEX_MAXWAIT);

}

Uint32 SDL_SemValue(SDL_sem *sem)

{

	Uint32 value;

	value = 0;

	if ( sem ) {

		SDL_LockMutex(sem->count_lock);

		value = sem->count;

		SDL_UnlockMutex(sem->count_lock);

	}

	return value;

}

int SDL_SemPost(SDL_sem *sem)

{

	if ( ! sem ) {

		SDL_SetError("Passed a NULL semaphore");

		return -1;

	}

	SDL_LockMutex(sem->count_lock);

	if ( sem->waiters_count > 0 ) {

		SDL_CondSignal(sem->count_nonzero);

	}

	++sem->count;

	SDL_UnlockMutex(sem->count_lock);

	return 0;

}

#endif /* SDL_THREADS_DISABLED */