nptl/pthread_barrier_wait.c

   1 /* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <sysdep.h>
  22 #include <lowlevellock.h>
  23 #include <pthreadP.h>
  24
  25
  26 /* Wait on barrier.  */
  27 int
  28 pthread_barrier_wait (barrier)
  29      pthread_barrier_t *barrier;
  30 {
  31   struct pthread_barrier *ibarrier = (struct pthread_barrier *) barrier;
  32   int result = 0;
  33
  34   /* Make sure we are alone.  */
  35   lll_lock (ibarrier->lock, ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  36
  37   /* One more arrival.  */
  38   --ibarrier->left;
  39
  40   /* Are these all?  */
  41   if (ibarrier->left == 0)
  42     {
  43       /* Yes. Increment the event counter to avoid invalid wake-ups and
  44          tell the current waiters that it is their turn.  */
  45       ++ibarrier->curr_event;
  46
  47       /* Wake up everybody.  */
  48       lll_futex_wake (&ibarrier->curr_event, INT_MAX,
  49                       ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  50
  51       /* This is the thread which finished the serialization.  */
  52       result = PTHREAD_BARRIER_SERIAL_THREAD;
  53     }
  54   else
  55     {
  56       /* The number of the event we are waiting for.  The barrier's event
  57          number must be bumped before we continue.  */
  58       unsigned int event = ibarrier->curr_event;
  59
  60       /* Before suspending, make the barrier available to others.  */
  61       lll_unlock (ibarrier->lock, ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  62
  63       /* Wait for the event counter of the barrier to change.  */
  64       do
  65         lll_futex_wait (&ibarrier->curr_event, event,
  66                         ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  67       while (event == ibarrier->curr_event);
  68     }
  69
  70   /* Make sure the init_count is stored locally or in a register.  */
  71   unsigned int init_count = ibarrier->init_count;
  72
  73   /* If this was the last woken thread, unlock.  */
  74   if (atomic_increment_val (&ibarrier->left) == init_count)
  75     /* We are done.  */
  76     lll_unlock (ibarrier->lock, ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  77
  78   return result;
  79 }