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/* Copyright (C) 2005, 2008, 2009, 2011 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 mutex synchronization

   mechanism for libgomp.  This type is private to the library.  This

   implementation uses atomic instructions and the futex syscall.  */

#include "wait.h"

long int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG;

long int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG;

void

gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval)

{

  /* First loop spins a while.  */

  while (oldval == 1)

    {

      if (do_spin (mutex, 1))

        {

          /* Spin timeout, nothing changed.  Set waiting flag.  */

          oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE);

          if (oldval == 0)

            return;

          futex_wait (mutex, -1);

          break;

        }

      else

        {

          /* Something changed.  If now unlocked, we're good to go.  */

          oldval = 0;

          if (__atomic_compare_exchange_n (mutex, &oldval, 1, false,

                                           MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))

            return;

        }

    }

  /* Second loop waits until mutex is unlocked.  We always exit this

     loop with wait flag set, so next unlock will awaken a thread.  */

  while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE)))

    do_wait (mutex, -1);

}

void

gomp_mutex_unlock_slow (gomp_mutex_t *mutex)

{

  futex_wake (mutex, 1);

}