src/thread/generic/SDL_syssem.c

/*
    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 */
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