pthread_barrier_wait.c

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/*-------------------------------------------------------------------------
 *
 * pthread_barrier_wait.c
 *    Implementation of pthread_barrier_t support for platforms lacking it.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/pthread_barrier_wait.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "c.h"
 
#include "port/pg_pthread.h"
 
int
pthread_barrier_init(pthread_barrier_t *barrier, const void *attr, int count)
{
    int         error;
 
    barrier->sense = false;
    barrier->count = count;
    barrier->arrived = 0;
    if ((error = pthread_cond_init(&barrier->cond, NULL)) != 0)
        return error;
    if ((error = pthread_mutex_init(&barrier->mutex, NULL)) != 0)
    {
        pthread_cond_destroy(&barrier->cond);
        return error;
    }
 
    return 0;
}
 
int
pthread_barrier_wait(pthread_barrier_t *barrier)
{
    bool        initial_sense;
 
    pthread_mutex_lock(&barrier->mutex);
 
    /* We have arrived at the barrier. */
    barrier->arrived++;
    Assert(barrier->arrived <= barrier->count);
 
    /* If we were the last to arrive, release the others and return. */
    if (barrier->arrived == barrier->count)
    {
        barrier->arrived = 0;
        barrier->sense = !barrier->sense;
        pthread_mutex_unlock(&barrier->mutex);
        pthread_cond_broadcast(&barrier->cond);
 
        return PTHREAD_BARRIER_SERIAL_THREAD;
    }
 
    /* Wait for someone else to flip the sense. */
    initial_sense = barrier->sense;
    do
    {
        pthread_cond_wait(&barrier->cond, &barrier->mutex);
    } while (barrier->sense == initial_sense);
 
    pthread_mutex_unlock(&barrier->mutex);
 
    return 0;
}
 
int
pthread_barrier_destroy(pthread_barrier_t *barrier)
{
    pthread_cond_destroy(&barrier->cond);
    pthread_mutex_destroy(&barrier->mutex);
    return 0;
}