src/thread/pthread/SDL_syssem.c
author Sam Lantinga <slouken@libsdl.org>
Fri, 06 Sep 2013 20:45:08 -0700
changeset 7732 4c0e4274c3f8
parent 7722 ea5565d856a8
child 7857 6388f5229bb7
permissions -rw-r--r--
Fixed time comparison and explicitly delay 1 ms instead of an arbitrary scheduled time.

/*
  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"

#include <errno.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/time.h>

#include "SDL_thread.h"
#include "SDL_timer.h"

/* Wrapper around POSIX 1003.1b semaphores */

#if defined(__MACOSX__) || defined(__IPHONEOS__)
/* Mac OS X doesn't support sem_getvalue() as of version 10.4 */
#include "../generic/SDL_syssem.c"
#else

struct SDL_semaphore
{
    sem_t sem;
};

/* Create a semaphore, initialized with value */
SDL_sem *
SDL_CreateSemaphore(Uint32 initial_value)
{
    SDL_sem *sem = (SDL_sem *) SDL_malloc(sizeof(SDL_sem));
    if (sem) {
        if (sem_init(&sem->sem, 0, initial_value) < 0) {
            SDL_SetError("sem_init() failed");
            SDL_free(sem);
            sem = NULL;
        }
    } else {
        SDL_OutOfMemory();
    }
    return sem;
}

void
SDL_DestroySemaphore(SDL_sem * sem)
{
    if (sem) {
        sem_destroy(&sem->sem);
        SDL_free(sem);
    }
}

int
SDL_SemTryWait(SDL_sem * sem)
{
    int retval;

    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }
    retval = SDL_MUTEX_TIMEDOUT;
    if (sem_trywait(&sem->sem) == 0) {
        retval = 0;
    }
    return retval;
}

int
SDL_SemWait(SDL_sem * sem)
{
    int retval;

    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }

    retval = sem_wait(&sem->sem);
    if (retval < 0) {
        retval = SDL_SetError("sem_wait() failed");
    }
    return retval;
}

int
SDL_SemWaitTimeout(SDL_sem * sem, Uint32 timeout)
{
    int retval;
#ifdef HAVE_SEM_TIMEDWAIT
    struct timeval now;
    struct timespec ts_timeout;
#else
    Uint32 end;
#endif

    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }

    /* Try the easy cases first */
    if (timeout == 0) {
        return SDL_SemTryWait(sem);
    }
    if (timeout == SDL_MUTEX_MAXWAIT) {
        return SDL_SemWait(sem);
    }

#ifdef HAVE_SEM_TIMEDWAIT
    /* Setup the timeout. sem_timedwait doesn't wait for
    * a lapse of time, but until we reach a certain time.
    * This time is now plus the timeout.
    */
    gettimeofday(&now, NULL);

    /* Add our timeout to current time */
    now.tv_usec += (timeout % 1000) * 1000;
    now.tv_sec += timeout / 1000;

    /* Wrap the second if needed */
    if ( now.tv_usec >= 1000000 ) {
        now.tv_usec -= 1000000;
        now.tv_sec ++;
    }

    /* Convert to timespec */
    ts_timeout.tv_sec = now.tv_sec;
    ts_timeout.tv_nsec = now.tv_usec * 1000;

    /* Wait. */
    do {
        retval = sem_timedwait(&sem->sem, &ts_timeout);
    } while (retval < 0 && errno == EINTR);

    if (retval < 0) {
        if (errno == ETIMEDOUT) {
            retval = SDL_MUTEX_TIMEDOUT;
        } else {
            SDL_SetError(strerror(errno));
        }
    }
#else
    end = SDL_GetTicks() + timeout;
    while ((retval = SDL_SemTryWait(sem)) == SDL_MUTEX_TIMEDOUT) {
        if ((Sint32)(SDL_GetTicks() - end) >= 0) {
            break;
        }
        SDL_Delay(1);
    }
#endif /* HAVE_SEM_TIMEDWAIT */

    return retval;
}

Uint32
SDL_SemValue(SDL_sem * sem)
{
    int ret = 0;
    if (sem) {
        sem_getvalue(&sem->sem, &ret);
        if (ret < 0) {
            ret = 0;
        }
    }
    return (Uint32) ret;
}

int
SDL_SemPost(SDL_sem * sem)
{
    int retval;

    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }

    retval = sem_post(&sem->sem);
    if (retval < 0) {
        SDL_SetError("sem_post() failed");
    }
    return retval;
}

#endif /* __MACOSX__ */
/* vi: set ts=4 sw=4 expandtab: */