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74 lines
2.2 KiB
C
74 lines
2.2 KiB
C
/* Copyright (C) 2002-2017 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 <lowlevellock.h>
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#include <futex-internal.h>
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#include <elide.h>
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#include <stdbool.h>
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int
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__pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
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{
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int result = EBUSY;
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bool wake = false;
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int futex_shared =
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rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
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if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
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rwlock->__data.__lock == 0
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&& rwlock->__data.__nr_readers == 0
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&& rwlock->__data.__writer, 0))
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return 0;
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lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
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if (rwlock->__data.__writer == 0
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&& (rwlock->__data.__nr_writers_queued == 0
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|| PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
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{
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if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
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{
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--rwlock->__data.__nr_readers;
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result = EAGAIN;
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}
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else
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{
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result = 0;
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/* See pthread_rwlock_rdlock. */
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if (rwlock->__data.__nr_readers == 1
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&& rwlock->__data.__nr_readers_queued > 0
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&& rwlock->__data.__nr_writers_queued > 0)
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{
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++rwlock->__data.__readers_wakeup;
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wake = true;
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}
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}
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}
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lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
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if (wake)
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futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
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return result;
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}
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strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)
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