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pthread_barrier.c revision 1.19 
      1 /*	$NetBSD: pthread_barrier.c,v 1.19 2009/01/29 21:19:35 ad Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2001, 2003, 2006, 2007, 2009 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Nathan J. Williams, by Jason R. Thorpe, and by Andrew Doran.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/cdefs.h>
     33 __RCSID("$NetBSD: pthread_barrier.c,v 1.19 2009/01/29 21:19:35 ad Exp $");
     34 
     35 #include <errno.h>
     36 
     37 #include "pthread.h"
     38 #include "pthread_int.h"
     39 
     40 int
     41 pthread_barrier_init(pthread_barrier_t *barrier,
     42 		     const pthread_barrierattr_t *attr, unsigned int count)
     43 {
     44 
     45 	if (attr != NULL && attr->ptba_magic != _PT_BARRIERATTR_MAGIC)
     46 		return EINVAL;
     47 	if (count == 0)
     48 		return EINVAL;
     49 
     50 	barrier->ptb_magic = _PT_BARRIER_MAGIC;
     51 	PTQ_INIT(&barrier->ptb_waiters);
     52 	barrier->ptb_initcount = count;
     53 	barrier->ptb_curcount = 0;
     54 	barrier->ptb_generation = 0;
     55 	return 0;
     56 }
     57 
     58 int
     59 pthread_barrier_destroy(pthread_barrier_t *barrier)
     60 {
     61 
     62 	if (barrier->ptb_magic != _PT_BARRIER_MAGIC)
     63 		return EINVAL;
     64 	if (barrier->ptb_curcount != 0)
     65 		return EBUSY;
     66 	return 0;
     67 }
     68 
     69 int
     70 pthread_barrier_wait(pthread_barrier_t *barrier)
     71 {
     72 	pthread_mutex_t *interlock;
     73 	pthread_t self;
     74 	unsigned int gen;
     75 
     76 	if (barrier->ptb_magic != _PT_BARRIER_MAGIC)
     77 		return EINVAL;
     78 
     79 	/*
     80 	 * A single arbitrary thread is supposed to return
     81 	 * PTHREAD_BARRIER_SERIAL_THREAD, and everone else
     82 	 * is supposed to return 0.  Since pthread_barrier_wait()
     83 	 * is not a cancellation point, this is trivial; we
     84 	 * simply elect that the thread that causes the barrier
     85 	 * to be satisfied gets the special return value.  Note
     86 	 * that this final thread does not actually need to block,
     87 	 * but instead is responsible for waking everyone else up.
     88 	 */
     89 	self = pthread__self();
     90 	interlock = pthread__hashlock(barrier);
     91 	pthread_mutex_lock(interlock);
     92 	if (barrier->ptb_curcount + 1 == barrier->ptb_initcount) {
     93 		barrier->ptb_generation++;
     94 		barrier->ptb_curcount = 0;
     95 		pthread__unpark_all(&barrier->ptb_waiters, self,
     96 		    interlock);
     97 		pthread_mutex_unlock(interlock);
     98 		return PTHREAD_BARRIER_SERIAL_THREAD;
     99 	}
    100 	barrier->ptb_curcount++;
    101 	gen = barrier->ptb_generation;
    102 	for (;;) {
    103 		PTQ_INSERT_TAIL(&barrier->ptb_waiters, self, pt_sleep);
    104 		self->pt_sleepobj = &barrier->ptb_waiters;
    105 		(void)pthread__park(self, interlock, &barrier->ptb_waiters,
    106 		    NULL, 0, __UNVOLATILE(&interlock->ptm_waiters));
    107 		if (__predict_true(gen != barrier->ptb_generation)) {
    108 			break;
    109 		}
    110 		pthread_mutex_lock(interlock);
    111 		if (gen != barrier->ptb_generation) {
    112 			pthread_mutex_unlock(interlock);
    113 			break;
    114 		}
    115 	}
    116 
    117 	return 0;
    118 }
    119 
    120 
    121 int
    122 pthread_barrierattr_init(pthread_barrierattr_t *attr)
    123 {
    124 
    125 	attr->ptba_magic = _PT_BARRIERATTR_MAGIC;
    126 	return 0;
    127 }
    128 
    129 int
    130 pthread_barrierattr_destroy(pthread_barrierattr_t *attr)
    131 {
    132 
    133 	if (attr->ptba_magic != _PT_BARRIERATTR_MAGIC)
    134 		return EINVAL;
    135 	attr->ptba_magic = _PT_BARRIERATTR_DEAD;
    136 	return 0;
    137 }
    138