fbtl/pthread_barrier_wait.c

   1 /* Copyright (C) 2003-2013 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <sysdep.h>
  21 #include <lowlevellock.h>
  22 #include <pthreadP.h>
  23
  24
  25 /* Wait on barrier.  */
  26 int
  27 pthread_barrier_wait (pthread_barrier_t *barrier)
  28 {
  29   struct pthread_barrier *ibarrier = (struct pthread_barrier *) barrier;
  30   int result = 0;
  31
  32   /* Make sure we are alone.  */
  33   lll_lock (ibarrier->lock, ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  34
  35   /* One more arrival.  */
  36   --ibarrier->left;
  37
  38   /* Are these all?  */
  39   if (ibarrier->left == 0)
  40     {
  41       /* Yes. Increment the event counter to avoid invalid wake-ups and
  42          tell the current waiters that it is their turn.  */
  43       ++ibarrier->curr_event;
  44
  45       /* Wake up everybody.  */
  46       lll_futex_wake (&ibarrier->curr_event, INT_MAX,
  47                       ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  48
  49       /* This is the thread which finished the serialization.  */
  50       result = PTHREAD_BARRIER_SERIAL_THREAD;
  51     }
  52   else
  53     {
  54       /* The number of the event we are waiting for.  The barrier's event
  55          number must be bumped before we continue.  */
  56       unsigned int event = ibarrier->curr_event;
  57
  58       /* Before suspending, make the barrier available to others.  */
  59       lll_unlock (ibarrier->lock, ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  60
  61       /* Wait for the event counter of the barrier to change.  */
  62       do
  63         lll_futex_wait (&ibarrier->curr_event, event,
  64                         ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  65       while (event == ibarrier->curr_event);
  66     }
  67
  68   /* Make sure the init_count is stored locally or in a register.  */
  69   unsigned int init_count = ibarrier->init_count;
  70
  71   /* If this was the last woken thread, unlock.  */
  72   if (atomic_increment_val (&ibarrier->left) == init_count)
  73     /* We are done.  */
  74     lll_unlock (ibarrier->lock, ibarrier->private ^ FUTEX_PRIVATE_FLAG);
  75
  76   return result;
  77 }