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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 barrier synchronization

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

   implementation uses atomic instructions and the futex syscall.  */

#include <limits.h>

#include "wait.h"

void

gomp_barrier_wait_end (gomp_barrier_t *bar, gomp_barrier_state_t state)

{

  if (__builtin_expect ((state & 1) != 0, 0))

    {

      /* Next time we'll be awaiting TOTAL threads again.  */

      bar->awaited = bar->total;

      __atomic_store_n (&bar->generation, bar->generation + 4,

                        MEMMODEL_RELEASE);

      futex_wake ((int *) &bar->generation, INT_MAX);

    }

  else

    {

      do

        do_wait ((int *) &bar->generation, state);

      while (__atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE) == state);

    }

}

void

gomp_barrier_wait (gomp_barrier_t *bar)

{

  gomp_barrier_wait_end (bar, gomp_barrier_wait_start (bar));

}

/* Like gomp_barrier_wait, except that if the encountering thread

   is not the last one to hit the barrier, it returns immediately.

   The intended usage is that a thread which intends to gomp_barrier_destroy

   this barrier calls gomp_barrier_wait, while all other threads

   call gomp_barrier_wait_last.  When gomp_barrier_wait returns,

   the barrier can be safely destroyed.  */

void

gomp_barrier_wait_last (gomp_barrier_t *bar)

{

  gomp_barrier_state_t state = gomp_barrier_wait_start (bar);

  if (state & 1)

    gomp_barrier_wait_end (bar, state);

}

void

gomp_team_barrier_wake (gomp_barrier_t *bar, int count)

{

  futex_wake ((int *) &bar->generation, count == 0 ? INT_MAX : count);

}

void

gomp_team_barrier_wait_end (gomp_barrier_t *bar, gomp_barrier_state_t state)

{

  unsigned int generation, gen;

  if (__builtin_expect ((state & 1) != 0, 0))

    {

      /* Next time we'll be awaiting TOTAL threads again.  */

      struct gomp_thread *thr = gomp_thread ();

      struct gomp_team *team = thr->ts.team;

      bar->awaited = bar->total;

      if (__builtin_expect (team->task_count, 0))

        {

          gomp_barrier_handle_tasks (state);

          state &= ~1;

        }

      else

        {

          __atomic_store_n (&bar->generation, state + 3, MEMMODEL_RELEASE);

          futex_wake ((int *) &bar->generation, INT_MAX);

          return;

        }

    }

  generation = state;

  do

    {

      do_wait ((int *) &bar->generation, generation);

      gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);

      if (__builtin_expect (gen & 1, 0))

        {

          gomp_barrier_handle_tasks (state);

          gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);

        }

      if ((gen & 2) != 0)

        generation |= 2;

    }

  while (gen != state + 4);

}

void

gomp_team_barrier_wait (gomp_barrier_t *bar)

{

  gomp_team_barrier_wait_end (bar, gomp_barrier_wait_start (bar));

}