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04277e02d7
* All files with FSF copyright notices: Update copyright dates using scripts/update-copyrights. * locale/programs/charmap-kw.h: Regenerated. * locale/programs/locfile-kw.h: Likewise.
45 lines
1.8 KiB
C
45 lines
1.8 KiB
C
/* Copyright (C) 2005-2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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 "pthreadP.h"
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int
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pthread_spin_unlock (pthread_spinlock_t *lock)
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{
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/* CONCURRENCTY NOTES:
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The atomic_exchange_rel synchronizes-with the atomic_exhange_acq in
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pthread_spin_lock.
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On hppa we must not use a plain `stw` to reset the guard lock. This
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has to do with the kernel compare-and-swap helper that is used to
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implement all of the atomic operations.
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The kernel CAS helper uses its own internal locks and that means that
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to create a true happens-before relationship between any two threads,
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the second thread must observe the internal lock having a value of 0
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(it must attempt to take the lock with ldcw). This creates the
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ordering required for a second thread to observe the effects of the
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RMW of the kernel CAS helper in any other thread.
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Therefore if a variable is used in an atomic macro it must always be
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manipulated with atomic macros in order for memory ordering rules to
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be preserved. */
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atomic_exchange_rel (lock, 0);
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return 0;
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}
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