config/linux/sem.c

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/* Copyright (C) 2005, 2008, 2009 Free Software Foundation, Inc.
   Contributed by Richard Henderson <rth@redhat.com>.

   This file is part of the GNU OpenMP Library (libgomp).

   Libgomp is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   more details.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

/* This is a Linux specific implementation of a semaphore synchronization
   mechanism for libgomp.  This type is private to the library.  This 
   implementation uses atomic instructions and the futex syscall.  */

#include "wait.h"


void
gomp_sem_wait_slow (gomp_sem_t *sem)
{
  while (1)
    {
      int val = __sync_val_compare_and_swap (sem, 0, -1);
      if (val > 0)
    {
      if (__sync_bool_compare_and_swap (sem, val, val - 1))
        return;
    }
      do_wait (sem, -1);
    }
}

void
gomp_sem_post_slow (gomp_sem_t *sem)
{
  int old, tmp = *sem, wake;

  do
    {
      old = tmp;
      wake = old > 0 ? old + 1 : 1;
      tmp = __sync_val_compare_and_swap (sem, old, wake);
    }
  while (old != tmp);

  futex_wake (sem, wake);
}

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