barrier.c revision 297077 
1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License, Version 1.0 only
6 * (the "License").  You may not use this file except in compliance
7 * with the License.
8 *
9 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10 * or http://www.opensolaris.org/os/licensing.
11 * See the License for the specific language governing permissions
12 * and limitations under the License.
13 *
14 * When distributing Covered Code, include this CDDL HEADER in each
15 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16 * If applicable, add the following below this CDDL HEADER, with the
17 * fields enclosed by brackets "[]" replaced with your own identifying
18 * information: Portions Copyright [yyyy] [name of copyright owner]
19 *
20 * CDDL HEADER END
21 */
22/*
23 * Copyright 2002 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27#pragma ident	"%Z%%M%	%I%	%E% SMI"
28
29/*
30 * This file implements a barrier, a synchronization primitive designed to allow
31 * threads to wait for each other at given points.  Barriers are initialized
32 * with a given number of threads, n, using barrier_init().  When a thread calls
33 * barrier_wait(), that thread blocks until n - 1 other threads reach the
34 * barrier_wait() call using the same barrier_t.  When n threads have reached
35 * the barrier, they are all awakened and sent on their way.  One of the threads
36 * returns from barrier_wait() with a return code of 1; the remaining threads
37 * get a return code of 0.
38 */
39
40#include <pthread.h>
41#ifdef illumos
42#include <synch.h>
43#endif
44#include <stdio.h>
45
46#include "barrier.h"
47
48void
49barrier_init(barrier_t *bar, int nthreads)
50{
51	pthread_mutex_init(&bar->bar_lock, NULL);
52#ifdef illumos
53	sema_init(&bar->bar_sem, 0, USYNC_THREAD, NULL);
54#else
55	sem_init(&bar->bar_sem, 0, 0);
56#endif
57
58	bar->bar_numin = 0;
59	bar->bar_nthr = nthreads;
60}
61
62int
63barrier_wait(barrier_t *bar)
64{
65	pthread_mutex_lock(&bar->bar_lock);
66
67	if (++bar->bar_numin < bar->bar_nthr) {
68		pthread_mutex_unlock(&bar->bar_lock);
69#ifdef illumos
70		sema_wait(&bar->bar_sem);
71#else
72		sem_wait(&bar->bar_sem);
73#endif
74
75		return (0);
76
77	} else {
78		int i;
79
80		/* reset for next use */
81		bar->bar_numin = 0;
82		for (i = 1; i < bar->bar_nthr; i++)
83#ifdef illumos
84			sema_post(&bar->bar_sem);
85#else
86			sem_post(&bar->bar_sem);
87#endif
88		pthread_mutex_unlock(&bar->bar_lock);
89
90		return (1);
91	}
92}
93