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/* Copyright (C) 2005-2014 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 & BAR_WAS_LAST, 0))
{
/* Next time we'll be awaiting TOTAL threads again. */
bar->awaited = bar->total;
__atomic_store_n (&bar->generation, bar->generation + BAR_INCR,
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 & BAR_WAS_LAST)
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 & BAR_WAS_LAST, 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;
team->work_share_cancelled = 0;
if (__builtin_expect (team->task_count, 0))
{
gomp_barrier_handle_tasks (state);
state &= ~BAR_WAS_LAST;
}
else
{
state &= ~BAR_CANCELLED;
state += BAR_INCR - BAR_WAS_LAST;
__atomic_store_n (&bar->generation, state, MEMMODEL_RELEASE);
futex_wake ((int *) &bar->generation, INT_MAX);
return;
}
}
generation = state;
state &= ~BAR_CANCELLED;
do
{
do_wait ((int *) &bar->generation, generation);
gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
if (__builtin_expect (gen & BAR_TASK_PENDING, 0))
{
gomp_barrier_handle_tasks (state);
gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
}
generation |= gen & BAR_WAITING_FOR_TASK;
}
while (gen != state + BAR_INCR);
}
void
gomp_team_barrier_wait (gomp_barrier_t *bar)
{
gomp_team_barrier_wait_end (bar, gomp_barrier_wait_start (bar));
}
void
gomp_team_barrier_wait_final (gomp_barrier_t *bar)
{
gomp_barrier_state_t state = gomp_barrier_wait_final_start (bar);
if (__builtin_expect (state & BAR_WAS_LAST, 0))
bar->awaited_final = bar->total;
gomp_team_barrier_wait_end (bar, state);
}
bool
gomp_team_barrier_wait_cancel_end (gomp_barrier_t *bar,
gomp_barrier_state_t state)
{
unsigned int generation, gen;
if (__builtin_expect (state & BAR_WAS_LAST, 0))
{
/* Next time we'll be awaiting TOTAL threads again. */
/* BAR_CANCELLED should never be set in state here, because
cancellation means that at least one of the threads has been
cancelled, thus on a cancellable barrier we should never see
all threads to arrive. */
struct gomp_thread *thr = gomp_thread ();
struct gomp_team *team = thr->ts.team;
bar->awaited = bar->total;
team->work_share_cancelled = 0;
if (__builtin_expect (team->task_count, 0))
{
gomp_barrier_handle_tasks (state);
state &= ~BAR_WAS_LAST;
}
else
{
state += BAR_INCR - BAR_WAS_LAST;
__atomic_store_n (&bar->generation, state, MEMMODEL_RELEASE);
futex_wake ((int *) &bar->generation, INT_MAX);
return false;
}
}
if (__builtin_expect (state & BAR_CANCELLED, 0))
return true;
generation = state;
do
{
do_wait ((int *) &bar->generation, generation);
gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
if (__builtin_expect (gen & BAR_CANCELLED, 0))
return true;
if (__builtin_expect (gen & BAR_TASK_PENDING, 0))
{
gomp_barrier_handle_tasks (state);
gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
}
generation |= gen & BAR_WAITING_FOR_TASK;
}
while (gen != state + BAR_INCR);
return false;
}
bool
gomp_team_barrier_wait_cancel (gomp_barrier_t *bar)
{
return gomp_team_barrier_wait_cancel_end (bar, gomp_barrier_wait_start (bar));
}
void
gomp_team_barrier_cancel (struct gomp_team *team)
{
gomp_mutex_lock (&team->task_lock);
if (team->barrier.generation & BAR_CANCELLED)
{
gomp_mutex_unlock (&team->task_lock);
return;
}
team->barrier.generation |= BAR_CANCELLED;
gomp_mutex_unlock (&team->task_lock);
futex_wake ((int *) &team->barrier.generation, INT_MAX);
}
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