SDL_syssem.c
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/*
SDL - Simple DirectMedia Layer
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Copyright (C) 1997-2009 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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*/
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#include "SDL_config.h"
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/* An implementation of semaphores using mutexes and condition variables */
#include "SDL_timer.h"
#include "SDL_thread.h"
#include "SDL_systhread_c.h"
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#if SDL_THREADS_DISABLED
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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;
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sem = (SDL_sem *)SDL_malloc(sizeof(*sem));
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if ( ! sem ) {
SDL_OutOfMemory();
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}
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);
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}
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}
/* 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);
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if ( sem->count_lock ) {
SDL_mutexP(sem->count_lock);
SDL_mutexV(sem->count_lock);
SDL_DestroyMutex(sem->count_lock);
}
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SDL_free(sem);
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}
}
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;
}
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#endif /* SDL_THREADS_DISABLED */