nptl/pthread_barrier_wait.c

   1 /* Copyright (C) 2003-2015 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 <futex-internal.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   int lll_private = ibarrier->private ^ FUTEX_PRIVATE_FLAG;
  34   int futex_private = (lll_private == LLL_PRIVATE
  35                        ? FUTEX_PRIVATE : FUTEX_SHARED);
  36
  37   /* Make sure we are alone.  */
  38   lll_lock (ibarrier->lock, lll_private);
  39
  40   /* One more arrival.  */
  41   --ibarrier->left;
  42
  43   /* Are these all?  */
  44   if (ibarrier->left == 0)
  45     {
  46       /* Yes. Increment the event counter to avoid invalid wake-ups and
  47          tell the current waiters that it is their turn.  */
  48       ++ibarrier->curr_event;
  49
  50       /* Wake up everybody.  */
  51       futex_wake (&ibarrier->curr_event, INT_MAX, futex_private);
  52
  53       /* This is the thread which finished the serialization.  */
  54       result = PTHREAD_BARRIER_SERIAL_THREAD;
  55     }
  56   else
  57     {
  58       /* The number of the event we are waiting for.  The barrier's event
  59          number must be bumped before we continue.  */
  60       unsigned int event = ibarrier->curr_event;
  61
  62       /* Before suspending, make the barrier available to others.  */
  63       lll_unlock (ibarrier->lock, lll_private);
  64
  65       /* Wait for the event counter of the barrier to change.  */
  66       do
  67         futex_wait_simple (&ibarrier->curr_event, event, futex_private);
  68       while (event == ibarrier->curr_event);
  69     }
  70
  71   /* Make sure the init_count is stored locally or in a register.  */
  72   unsigned int init_count = ibarrier->init_count;
  73
  74   /* If this was the last woken thread, unlock.  */
  75   if (atomic_increment_val (&ibarrier->left) == init_count)
  76     /* We are done.  */
  77     lll_unlock (ibarrier->lock, lll_private);
  78
  79   return result;
  80 }
  81 weak_alias (__pthread_barrier_wait, pthread_barrier_wait)