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/*
* Authors: Martin Nagy <mnagy@redhat.com>
*
* Copyright (C) 2008 Red Hat
* see file 'COPYING' for use and warranty information
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; version 2 or later
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Note: This implementation doesn't prevent from starvation. This means that
* if a thread signals the semaphore and then waits for it, it may catch it's
* own signal. However, for our purposes, this shouldn't be needed.
*/
#include <isc/condition.h>
#include <isc/result.h>
#include <isc/util.h>
#include "semaphore.h"
/*
* Initialize a semaphore.
*
* sem - allocated semaphore that will be initialized
* value - number of times we can acquire the semaphore.
*/
isc_result_t
semaphore_init(semaphore_t *sem, int value)
{
isc_result_t result;
REQUIRE(sem != NULL);
REQUIRE(value > 0);
sem->value = value;
result = isc_mutex_init(&sem->mutex);
if (result != ISC_R_SUCCESS)
return result;
result = isc_condition_init(&sem->cond);
if (result != ISC_R_SUCCESS)
isc_mutex_destroy(&sem->mutex);
return result;
}
/*
* Destroy a semaphore.
*
* sem - semaphore to be destroyed.
*/
void
semaphore_destroy(semaphore_t *sem)
{
if (sem == NULL)
return;
RUNTIME_CHECK(isc_mutex_destroy(&sem->mutex) == ISC_R_SUCCESS);
RUNTIME_CHECK(isc_condition_destroy(&sem->cond) == ISC_R_SUCCESS);
}
/*
* Wait on semaphore. This operation will try to acquire a lock on the
* semaphore. If the semaphore is already acquired as many times at it allows,
* the function will block until someone releases the lock.
*/
void
semaphore_wait(semaphore_t *sem)
{
REQUIRE(sem != NULL);
LOCK(&sem->mutex);
sem->value--;
if (sem->value < 0)
WAIT(&sem->cond, &sem->mutex);
UNLOCK(&sem->mutex);
}
/*
* Release the semaphore. This will make sure that another thread (probably
* already waiting) will be able to acquire the semaphore.
*/
void
semaphore_signal(semaphore_t *sem)
{
REQUIRE(sem != NULL);
LOCK(&sem->mutex);
sem->value++;
if (sem->value >= 0)
SIGNAL(&sem->cond);
UNLOCK(&sem->mutex);
}
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