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/* Copyright (C) 2003-2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
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 <sysdep.h>
#include <lowlevellock.h>
#include <futex-internal.h>
#include <pthread.h>
#include <pthreadP.h>
#include <stap-probe.h>
#include <elide.h>
/* Unlock RWLOCK. */
int
__pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
int futex_shared =
rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
LIBC_PROBE (rwlock_unlock, 1, rwlock);
/* Trying to elide an unlocked lock may crash the process. This
is expected and is compatible with POSIX.1-2008: "results are
undefined if the read-write lock rwlock is not held by the
calling thread". */
if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
&& rwlock->__data.__nr_readers == 0))
return 0;
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
if (rwlock->__data.__writer)
rwlock->__data.__writer = 0;
else
--rwlock->__data.__nr_readers;
/* If there are still readers present, we do not yet need to wake writers
nor are responsible to wake any readers. */
if (rwlock->__data.__nr_readers == 0)
{
/* Note that if there is a blocked writer, we effectively make it
responsible for waking any readers because we don't wake readers in
this case. */
if (rwlock->__data.__nr_writers_queued)
{
++rwlock->__data.__writer_wakeup;
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
return 0;
}
else if (rwlock->__data.__nr_readers_queued)
{
++rwlock->__data.__readers_wakeup;
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
futex_shared);
return 0;
}
}
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
return 0;
}
weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
hidden_def (__pthread_rwlock_unlock)
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