semaphore.h

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/*
 * Copyright (c) 2005 Zmanda, Inc.  All Rights Reserved.
 * 
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License version 2.1 as 
 * published by the Free Software Foundation.
 * 
 * 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA.
 * 
 * Contact information: Zmanda Inc., 505 N Mathlida Ave, Suite 120
 * Sunnyvale, CA 94085, USA, or: http://www.zmanda.com
 */

/* GLib does not provide semaphores, which are useful in queue.c.
   So, we implement it here. */

#include <glib.h>

#ifndef SEMAPHORE_H

typedef struct {
    int value;
    GMutex *mutex;
    GCond * decrement_cond;
    GCond * zero_cond;
} semaphore_t;

/* Create a new semaphore object with the given value.
 *
 * @param value: new value
 * @returns: newly allocated semaphore_t
 */
semaphore_t* semaphore_new_with_value(int value);

/* Shortcut to make a new semaphore with value 1.
 */
#define semaphore_new() semaphore_new_with_value(1)

/* Free a semaphore allocated by semaphore_with_new_value().  Be sure the
 * semaphore is no longer in use by any threads.
 *
 * @param sem: the semaphore to free
 */
void semaphore_free(semaphore_t *sem);

/* Increment the value of the semaphore by incr.  This corresponds to
 * Dijkstra's V(), or the typical semaphore's release().
 *
 * This function will not block, but may wake other threads waiting
 * on semaphore_decrement().
 *
 * @param sem: the semaphore
 * @param incr: added to the semaphore's value
 */
void semaphore_increment(semaphore_t *sem, unsigned int incr);

/* Shortcut to increment the semaphore by 1.
 */
#define semaphore_up(semaphore) semphore_increment(semaphore,1)

/* Decrement the value of the semaphore by incr.  If this operation
 * would make the semaphore zero or less, block until the semaphore
 * value is large enough, then perform the decerement operation. Threads
 * waiting on semaphore_wait_empty() may be awakened if the value
 * reaches 0.
 *
 * @param sem: the semaphore
 * @param decr: subtracted from the semaphore's value
 */
void semaphore_decrement(semaphore_t *sem, unsigned int decr);

/* Shortcut to decrement the semaphore by 1.
 */
#define semaphore_down(semaphore) semaphore_decrement(semaphore, 1)

/* Increment or decrement (with a negative incr) the value without
 * blocking.  Threads waiting on semaphore_decrement() or
 * semaphore_wait_empty() will be awakened if necessary.
 *
 * @param sem: the semaphore
 * @param incr: added to the semaphore's value
 */
void semaphore_force_adjust(semaphore_t *sem, int incr);

/* Set the semaphore to a given value without blocking.  Threads
 * waiting on semaphore_decrement() or semaphore_wait_empty()
 * will be awakened if necessary.
 *
 * @param sem: the semaphore
 * @param value: the new value
 */
void semaphore_force_set(semaphore_t *sem, int value);

/* Block until the semaphore's value is zero.
 *
 * @param sem: the semaphore
 */
void semaphore_wait_empty(semaphore_t *sem);

#endif /* SEMAPHORE_H */