sem.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * David M. Lee, II <[email protected]>
 *
 * 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