252 lines
8.2 KiB
C
252 lines
8.2 KiB
C
/* Copyright (C) 2005-2014 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU OpenMP Library (libgomp).
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Libgomp is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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/* This file handles the ORDERED construct. */
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#include "libgomp.h"
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/* This function is called when first allocating an iteration block. That
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is, the thread is not currently on the queue. The work-share lock must
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be held on entry. */
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void
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gomp_ordered_first (void)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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struct gomp_work_share *ws = thr->ts.work_share;
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unsigned index;
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/* Work share constructs can be orphaned. */
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if (team == NULL || team->nthreads == 1)
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return;
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index = ws->ordered_cur + ws->ordered_num_used;
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if (index >= team->nthreads)
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index -= team->nthreads;
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ws->ordered_team_ids[index] = thr->ts.team_id;
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/* If this is the first and only thread in the queue, then there is
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no one to release us when we get to our ordered section. Post to
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our own release queue now so that we won't block later. */
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if (ws->ordered_num_used++ == 0)
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gomp_sem_post (team->ordered_release[thr->ts.team_id]);
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}
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/* This function is called when completing the last iteration block. That
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is, there are no more iterations to perform and so the thread should be
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removed from the queue entirely. Because of the way ORDERED blocks are
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managed, it follows that we currently own access to the ORDERED block,
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and should now pass it on to the next thread. The work-share lock must
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be held on entry. */
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void
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gomp_ordered_last (void)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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struct gomp_work_share *ws = thr->ts.work_share;
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unsigned next_id;
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/* Work share constructs can be orphaned. */
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if (team == NULL || team->nthreads == 1)
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return;
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/* We're no longer the owner. */
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ws->ordered_owner = -1;
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/* If we're not the last thread in the queue, then wake the next. */
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if (--ws->ordered_num_used > 0)
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{
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unsigned next = ws->ordered_cur + 1;
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if (next == team->nthreads)
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next = 0;
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ws->ordered_cur = next;
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next_id = ws->ordered_team_ids[next];
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gomp_sem_post (team->ordered_release[next_id]);
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}
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}
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/* This function is called when allocating a subsequent allocation block.
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That is, we're done with the current iteration block and we're allocating
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another. This is the logical combination of a call to gomp_ordered_last
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followed by a call to gomp_ordered_first. The work-share lock must be
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held on entry. */
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void
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gomp_ordered_next (void)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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struct gomp_work_share *ws = thr->ts.work_share;
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unsigned index, next_id;
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/* Work share constructs can be orphaned. */
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if (team == NULL || team->nthreads == 1)
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return;
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/* We're no longer the owner. */
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ws->ordered_owner = -1;
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/* If there's only one thread in the queue, that must be us. */
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if (ws->ordered_num_used == 1)
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{
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/* We have a similar situation as in gomp_ordered_first
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where we need to post to our own release semaphore. */
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gomp_sem_post (team->ordered_release[thr->ts.team_id]);
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return;
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}
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/* If the queue is entirely full, then we move ourself to the end of
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the queue merely by incrementing ordered_cur. Only if it's not
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full do we have to write our id. */
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if (ws->ordered_num_used < team->nthreads)
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{
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index = ws->ordered_cur + ws->ordered_num_used;
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if (index >= team->nthreads)
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index -= team->nthreads;
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ws->ordered_team_ids[index] = thr->ts.team_id;
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}
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index = ws->ordered_cur + 1;
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if (index == team->nthreads)
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index = 0;
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ws->ordered_cur = index;
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next_id = ws->ordered_team_ids[index];
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gomp_sem_post (team->ordered_release[next_id]);
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}
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/* This function is called when a statically scheduled loop is first
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being created. */
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void
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gomp_ordered_static_init (void)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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if (team == NULL || team->nthreads == 1)
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return;
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gomp_sem_post (team->ordered_release[0]);
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}
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/* This function is called when a statically scheduled loop is moving to
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the next allocation block. Static schedules are not first come first
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served like the others, so we're to move to the numerically next thread,
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not the next thread on a list. The work-share lock should *not* be held
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on entry. */
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void
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gomp_ordered_static_next (void)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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struct gomp_work_share *ws = thr->ts.work_share;
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unsigned id = thr->ts.team_id;
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if (team == NULL || team->nthreads == 1)
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return;
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ws->ordered_owner = -1;
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/* This thread currently owns the lock. Increment the owner. */
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if (++id == team->nthreads)
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id = 0;
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ws->ordered_team_ids[0] = id;
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gomp_sem_post (team->ordered_release[id]);
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}
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/* This function is called when we need to assert that the thread owns the
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ordered section. Due to the problem of posted-but-not-waited semaphores,
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this needs to happen before completing a loop iteration. */
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void
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gomp_ordered_sync (void)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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struct gomp_work_share *ws = thr->ts.work_share;
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/* Work share constructs can be orphaned. But this clearly means that
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we are the only thread, and so we automatically own the section. */
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if (team == NULL || team->nthreads == 1)
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return;
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/* ??? I believe it to be safe to access this data without taking the
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ws->lock. The only presumed race condition is with the previous
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thread on the queue incrementing ordered_cur such that it points
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to us, concurrently with our check below. But our team_id is
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already present in the queue, and the other thread will always
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post to our release semaphore. So the two cases are that we will
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either win the race an momentarily block on the semaphore, or lose
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the race and find the semaphore already unlocked and so not block.
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Either way we get correct results.
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However, there is an implicit flush on entry to an ordered region,
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so we do need to have a barrier here. If we were taking a lock
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this could be MEMMODEL_RELEASE since the acquire would be coverd
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by the lock. */
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__atomic_thread_fence (MEMMODEL_ACQ_REL);
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if (ws->ordered_owner != thr->ts.team_id)
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{
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gomp_sem_wait (team->ordered_release[thr->ts.team_id]);
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ws->ordered_owner = thr->ts.team_id;
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}
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}
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/* This function is called by user code when encountering the start of an
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ORDERED block. We must check to see if the current thread is at the
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head of the queue, and if not, block. */
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#ifdef HAVE_ATTRIBUTE_ALIAS
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extern void GOMP_ordered_start (void)
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__attribute__((alias ("gomp_ordered_sync")));
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#else
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void
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GOMP_ordered_start (void)
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{
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gomp_ordered_sync ();
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}
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#endif
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/* This function is called by user code when encountering the end of an
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ORDERED block. With the current ORDERED implementation there's nothing
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for us to do.
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However, the current implementation has a flaw in that it does not allow
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the next thread into the ORDERED section immediately after the current
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thread exits the ORDERED section in its last iteration. The existance
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of this function allows the implementation to change. */
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void
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GOMP_ordered_end (void)
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{
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}
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