linuxthreads/barrier.c

   1 /* POSIX barrier implementation for LinuxThreads.
   2    Copyright (C) 2000, 2003 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Kaz Kylheku <kaz@ashi.footprints.net>, 2000.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public License as
   8    published by the Free Software Foundation; either version 2.1 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <errno.h>
  22 #include "pthread.h"
  23 #include "internals.h"
  24 #include "spinlock.h"
  25 #include "queue.h"
  26 #include "restart.h"
  27
  28 int
  29 pthread_barrier_wait(pthread_barrier_t *barrier)
  30 {
  31   pthread_descr self = thread_self();
  32   pthread_descr temp_wake_queue, th;
  33   int result = 0;
  34
  35   __pthread_lock(&barrier->__ba_lock, self);
  36
  37   /* If the required number of threads have achieved rendezvous... */
  38   if (barrier->__ba_present >= barrier->__ba_required - 1)
  39     {
  40       /* ... then this last caller shall be the serial thread */
  41       result = PTHREAD_BARRIER_SERIAL_THREAD;
  42       /* Copy and clear wait queue and reset barrier. */
  43       temp_wake_queue = barrier->__ba_waiting;
  44       barrier->__ba_waiting = NULL;
  45       barrier->__ba_present = 0;
  46     }
  47   else
  48     {
  49       result = 0;
  50       barrier->__ba_present++;
  51       enqueue(&barrier->__ba_waiting, self);
  52     }
  53
  54   __pthread_unlock(&barrier->__ba_lock);
  55
  56   if (result == 0)
  57     {
  58       /* Non-serial threads have to suspend */
  59       suspend(self);
  60       /* We don't bother dealing with cancellation because the POSIX
  61          spec for barriers doesn't mention that pthread_barrier_wait
  62          is a cancellation point. */
  63     }
  64   else
  65     {
  66       /* Serial thread wakes up all others. */
  67       while ((th = dequeue(&temp_wake_queue)) != NULL)
  68         restart(th);
  69     }
  70
  71   return result;
  72 }
  73
  74 int
  75 pthread_barrier_init(pthread_barrier_t *barrier,
  76                                 const pthread_barrierattr_t *attr,
  77                                 unsigned int count)
  78 {
  79   if (count == 0)
  80      return EINVAL;
  81
  82   __pthread_init_lock(&barrier->__ba_lock);
  83   barrier->__ba_required = count;
  84   barrier->__ba_present = 0;
  85   barrier->__ba_waiting = NULL;
  86   return 0;
  87 }
  88
  89 int
  90 pthread_barrier_destroy(pthread_barrier_t *barrier)
  91 {
  92   if (barrier->__ba_waiting != NULL) return EBUSY;
  93   return 0;
  94 }
  95
  96 int
  97 pthread_barrierattr_init(pthread_barrierattr_t *attr)
  98 {
  99   attr->__pshared = PTHREAD_PROCESS_PRIVATE;
 100   return 0;
 101 }
 102
 103 int
 104 pthread_barrierattr_destroy(pthread_barrierattr_t *attr)
 105 {
 106   return 0;
 107 }
 108
 109 int
 110 __pthread_barrierattr_getpshared(const pthread_barrierattr_t *attr,
 111                                  int *pshared)
 112 {
 113   *pshared = PTHREAD_PROCESS_PRIVATE;
 114   return 0;
 115 }
 116
 117 int
 118 pthread_barrierattr_setpshared(pthread_barrierattr_t *attr, int pshared)
 119 {
 120   if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED)
 121     return EINVAL;
 122
 123   /* For now it is not possible to shared a conditional variable.  */
 124   if (pshared != PTHREAD_PROCESS_PRIVATE)
 125     return ENOSYS;
 126
 127   return 0;
 128 }