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/* Copyright (C) 2002-2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <errno.h>
#include "pthreadP.h"
#include <lowlevellock.h>
#include <futex-internal.h>
#include <elide.h>
#include <stdbool.h>
int
__pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
int result = EBUSY;
bool wake = false;
int futex_shared =
rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
rwlock->__data.__lock == 0
&& rwlock->__data.__nr_readers == 0
&& rwlock->__data.__writer, 0))
return 0;
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
if (rwlock->__data.__writer == 0
&& (rwlock->__data.__nr_writers_queued == 0
|| PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
{
if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
{
--rwlock->__data.__nr_readers;
result = EAGAIN;
}
else
{
result = 0;
/* See pthread_rwlock_rdlock. */
if (rwlock->__data.__nr_readers == 1
&& rwlock->__data.__nr_readers_queued > 0
&& rwlock->__data.__nr_writers_queued > 0)
{
++rwlock->__data.__readers_wakeup;
wake = true;
}
}
}
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
if (wake)
futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
return result;
}
strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)
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