sem.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * David M. Lee, II <dlee@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*! \file
 *
 * \brief Asterisk semaphore support.
 */
 
#include "asterisk.h"
 
#include "asterisk/sem.h"
#include "asterisk/utils.h"
 
#ifndef HAS_WORKING_SEMAPHORE
 
/* DIY semaphores! */
 
int ast_sem_init(struct ast_sem *sem, int pshared, unsigned int value)
{
    if (pshared) {
        /* Don't need it... yet */
        errno = ENOSYS;
        return -1;
    }
 
    /* Since value is unsigned, this will also catch attempts to init with
     * a negative value */
    if (value > AST_SEM_VALUE_MAX) {
        errno = EINVAL;
        return -1;
    }
 
    sem->count = value;
    sem->waiters = 0;
    ast_mutex_init(&sem->mutex);
    ast_cond_init(&sem->cond, NULL);
    return 0;
}
 
int ast_sem_destroy(struct ast_sem *sem)
{
    ast_mutex_destroy(&sem->mutex);
    ast_cond_destroy(&sem->cond);
    return 0;
}
 
int ast_sem_post(struct ast_sem *sem)
{
    SCOPED_MUTEX(lock, &sem->mutex);
 
    ast_assert(sem->count >= 0);
 
    if (sem->count == AST_SEM_VALUE_MAX) {
        errno = EOVERFLOW;
        return -1;
    }
 
    /* Give it up! */
    ++sem->count;
 
    /* Release a waiter, if needed */
    if (sem->waiters) {
        ast_cond_signal(&sem->cond);
    }
 
    return 0;
}
 
int ast_sem_wait(struct ast_sem *sem)
{
    int res;
    SCOPED_MUTEX(lock, &sem->mutex);
 
    ast_assert(sem->count >= 0);
 
    /* Wait for a non-zero count */
    ++sem->waiters;
    while (sem->count == 0) {
        res = ast_cond_wait(&sem->cond, &sem->mutex);
        /* Give up on error */
        if (res != 0) {
            --sem->waiters;
            return res;
        }
    }
    --sem->waiters;
 
    /* Take it! */
    --sem->count;
 
    return 0;
}
 
int ast_sem_timedwait(struct ast_sem *sem, const struct timespec *abs_timeout)
{
    int res;
    SCOPED_MUTEX(lock, &sem->mutex);
 
    ast_assert(sem->count >= 0);
 
    /* Wait for a non-zero count */
    ++sem->waiters;
    while (sem->count == 0) {
        res = ast_cond_timedwait(&sem->cond, &sem->mutex, abs_timeout);
        /* Give up on error */
        if (res != 0) {
            --sem->waiters;
            return res;
        }
    }
    --sem->waiters;
 
    /* Take it! */
    --sem->count;
 
    return 0;
}
 
int ast_sem_getvalue(struct ast_sem *sem, int *sval)
{
    SCOPED_MUTEX(lock, &sem->mutex);
 
    ast_assert(sem->count >= 0);
 
    *sval = sem->count;
 
    return 0;
}
 
#endif