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62 lines
2.5 KiB
C
62 lines
2.5 KiB
C
/* Copyright (C) 2002-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include "pthreadP.h"
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#include <atomic.h>
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#include <futex-internal.h>
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int
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pthread_barrier_destroy (pthread_barrier_t *barrier)
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{
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struct pthread_barrier *bar = (struct pthread_barrier *) barrier;
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/* Destroying a barrier is only allowed if no thread is blocked on it.
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Thus, there is no unfinished round, and all modifications to IN will
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have happened before us (either because the calling thread took part
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in the most recent round and thus synchronized-with all other threads
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entering, or the program ensured this through other synchronization).
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We must wait until all threads that entered so far have confirmed that
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they have exited as well. To get the notification, pretend that we have
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reached the reset threshold. */
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unsigned int count = bar->count;
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unsigned int max_in_before_reset = BARRIER_IN_THRESHOLD
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- BARRIER_IN_THRESHOLD % count;
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/* Relaxed MO sufficient because the program must have ensured that all
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modifications happen-before this load (see above). */
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unsigned int in = atomic_load_relaxed (&bar->in);
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/* Trigger reset. The required acquire MO is below. */
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if (atomic_fetch_add_relaxed (&bar->out, max_in_before_reset - in) < in)
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{
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/* Not all threads confirmed yet that they have exited, so another
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thread will perform a reset. Wait until that has happened. */
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while (in != 0)
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{
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futex_wait_simple (&bar->in, in, bar->shared);
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in = atomic_load_relaxed (&bar->in);
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}
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}
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/* We must ensure that memory reuse happens after all prior use of the
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barrier (specifically, synchronize-with the reset of the barrier or the
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confirmation of threads leaving the barrier). */
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atomic_thread_fence_acquire ();
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return 0;
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}
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