src/port/pthread_barrier_wait.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pthread_barrier_wait.c
   4  *    Implementation of pthread_barrier_t support for platforms lacking it.
   5  *
   6  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   7  *
   8  * IDENTIFICATION
   9  *    src/port/pthread_barrier_wait.c
  10  *
  11  *-------------------------------------------------------------------------
  12  */
  13
  14 #include "c.h"
  15
  16 #include "port/pg_pthread.h"
  17
  18 int
  19 pthread_barrier_init(pthread_barrier_t *barrier, const void *attr, int count)
  20 {
  21         int                     error;
  22
  23         barrier->sense = false;
  24         barrier->count = count;
  25         barrier->arrived = 0;
  26         if ((error = pthread_cond_init(&barrier->cond, NULL)) != 0)
  27                 return error;
  28         if ((error = pthread_mutex_init(&barrier->mutex, NULL)) != 0)
  29         {
  30                 pthread_cond_destroy(&barrier->cond);
  31                 return error;
  32         }
  33
  34         return 0;
  35 }
  36
  37 int
  38 pthread_barrier_wait(pthread_barrier_t *barrier)
  39 {
  40         bool            initial_sense;
  41
  42         pthread_mutex_lock(&barrier->mutex);
  43
  44         /* We have arrived at the barrier. */
  45         barrier->arrived++;
  46         Assert(barrier->arrived <= barrier->count);
  47
  48         /* If we were the last to arrive, release the others and return. */
  49         if (barrier->arrived == barrier->count)
  50         {
  51                 barrier->arrived = 0;
  52                 barrier->sense = !barrier->sense;
  53                 pthread_mutex_unlock(&barrier->mutex);
  54                 pthread_cond_broadcast(&barrier->cond);
  55
  56                 return PTHREAD_BARRIER_SERIAL_THREAD;
  57         }
  58
  59         /* Wait for someone else to flip the sense. */
  60         initial_sense = barrier->sense;
  61         do
  62         {
  63                 pthread_cond_wait(&barrier->cond, &barrier->mutex);
  64         } while (barrier->sense == initial_sense);
  65
  66         pthread_mutex_unlock(&barrier->mutex);
  67
  68         return 0;
  69 }
  70
  71 int
  72 pthread_barrier_destroy(pthread_barrier_t *barrier)
  73 {
  74         pthread_cond_destroy(&barrier->cond);
  75         pthread_mutex_destroy(&barrier->mutex);
  76         return 0;
  77 }