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      1 /*	$NetBSD: pthread_barrier.c,v 1.23 2022/02/12 14:59:32 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2001, 2003, 2006, 2007, 2009, 2020 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 1.23 2022/02/12 14:59:32 riastradh Exp $");
     34 
     35 /* Need to use libc-private names for atomic operations. */
     36 #include "../../common/lib/libc/atomic/atomic_op_namespace.h"
     37 
     38 #include <errno.h>
     39 
     40 #include "pthread.h"
     41 #include "pthread_int.h"
     42 
     43 int
     44 pthread_barrier_init(pthread_barrier_t *barrier,
     45 		     const pthread_barrierattr_t *attr, unsigned int count)
     46 {
     47 
     48 	pthread__error(EINVAL, "Invalid barrier attribute",
     49 	    attr == NULL || attr->ptba_magic == _PT_BARRIERATTR_MAGIC);
     50 	if (count == 0)
     51 		return EINVAL;
     52 
     53 	barrier->ptb_magic = _PT_BARRIER_MAGIC;
     54 	PTQ_INIT(&barrier->ptb_waiters);
     55 	barrier->ptb_initcount = count;
     56 	barrier->ptb_curcount = 0;
     57 	barrier->ptb_generation = 0;
     58 	return 0;
     59 }
     60 
     61 int
     62 pthread_barrier_destroy(pthread_barrier_t *barrier)
     63 {
     64 
     65 	pthread__error(EINVAL, "Invalid barrier",
     66 	    barrier->ptb_magic == _PT_BARRIER_MAGIC);
     67 	if (barrier->ptb_curcount != 0)
     68 		return EBUSY;
     69 
     70 	barrier->ptb_magic = _PT_BARRIER_DEAD;
     71 
     72 	return 0;
     73 }
     74 
     75 int
     76 pthread_barrier_wait(pthread_barrier_t *barrier)
     77 {
     78 	pthread_mutex_t *interlock;
     79 	pthread_t self;
     80 	unsigned int gen;
     81 
     82 	pthread__error(EINVAL, "Invalid barrier",
     83 	    barrier->ptb_magic == _PT_BARRIER_MAGIC);
     84 
     85 	/*
     86 	 * A single arbitrary thread is supposed to return
     87 	 * PTHREAD_BARRIER_SERIAL_THREAD, and everone else
     88 	 * is supposed to return 0.  Since pthread_barrier_wait()
     89 	 * is not a cancellation point, this is trivial; we
     90 	 * simply elect that the thread that causes the barrier
     91 	 * to be satisfied gets the special return value.  Note
     92 	 * that this final thread does not actually need to block,
     93 	 * but instead is responsible for waking everyone else up.
     94 	 */
     95 	self = pthread__self();
     96 	interlock = pthread__hashlock(barrier);
     97 	pthread_mutex_lock(interlock);
     98 	if (barrier->ptb_curcount + 1 == barrier->ptb_initcount) {
     99 		barrier->ptb_generation++;
    100 		barrier->ptb_curcount = 0;
    101 		pthread__unpark_all(&barrier->ptb_waiters, self,
    102 		    interlock);
    103 		pthread_mutex_unlock(interlock);
    104 		return PTHREAD_BARRIER_SERIAL_THREAD;
    105 	}
    106 	barrier->ptb_curcount++;
    107 	gen = barrier->ptb_generation;
    108 	for (;;) {
    109 		PTQ_INSERT_TAIL(&barrier->ptb_waiters, self, pt_sleep);
    110 		self->pt_sleepobj = &barrier->ptb_waiters;
    111 		(void)pthread__park(self, interlock, &barrier->ptb_waiters,
    112 		    NULL, 0);
    113 		if (__predict_true(gen != barrier->ptb_generation)) {
    114 			break;
    115 		}
    116 		pthread_mutex_lock(interlock);
    117 		if (gen != barrier->ptb_generation) {
    118 			pthread_mutex_unlock(interlock);
    119 			break;
    120 		}
    121 	}
    122 
    123 	return 0;
    124 }
    125 
    126 #ifdef _PTHREAD_PSHARED
    127 int
    128 pthread_barrierattr_getpshared(const pthread_barrierattr_t * __restrict attr,
    129     int * __restrict pshared)
    130 {
    131 
    132 	pthread__error(EINVAL, "Invalid barrier attribute",
    133 	    attr->ptba_magic == _PT_BARRIERATTR_MAGIC);
    134 
    135 	*pshared = PTHREAD_PROCESS_PRIVATE;
    136 	return 0;
    137 }
    138 
    139 int
    140 pthread_barrierattr_setpshared(pthread_barrierattr_t *attr, int pshared)
    141 {
    142 
    143 	pthread__error(EINVAL, "Invalid barrier attribute",
    144 	    attr->ptba_magic == _PT_BARRIERATTR_MAGIC);
    145 
    146 	switch(pshared) {
    147 	case PTHREAD_PROCESS_PRIVATE:
    148 		return 0;
    149 	case PTHREAD_PROCESS_SHARED:
    150 		return ENOSYS;
    151 	}
    152 	return EINVAL;
    153 }
    154 #endif
    155 
    156 int
    157 pthread_barrierattr_init(pthread_barrierattr_t *attr)
    158 {
    159 
    160 	attr->ptba_magic = _PT_BARRIERATTR_MAGIC;
    161 	return 0;
    162 }
    163 
    164 int
    165 pthread_barrierattr_destroy(pthread_barrierattr_t *attr)
    166 {
    167 
    168 	pthread__error(EINVAL, "Invalid barrier attribute",
    169 	    attr->ptba_magic == _PT_BARRIERATTR_MAGIC);
    170 	attr->ptba_magic = _PT_BARRIERATTR_DEAD;
    171 	return 0;
    172 }
    173