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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>
/* Acquire write lock for RWLOCK. */
static int __attribute__((noinline))
__pthread_rwlock_wrlock_slow (pthread_rwlock_t *rwlock)
{
int result = 0;
int futex_shared =
rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
/* Caller has taken the lock. */
while (1)
{
/* Make sure we are not holding the rwlock as a writer. This is
a deadlock situation we recognize and report. */
if (__builtin_expect (rwlock->__data.__writer
== THREAD_GETMEM (THREAD_SELF, tid), 0))
{
result = EDEADLK;
break;
}
/* Remember that we are a writer. */
if (++rwlock->__data.__nr_writers_queued == 0)
{
/* Overflow on number of queued writers. */
--rwlock->__data.__nr_writers_queued;
result = EAGAIN;
break;
}
int waitval = rwlock->__data.__writer_wakeup;
/* Free the lock. */
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
/* Wait for the writer or reader(s) to finish. We do not check the
return value because we decide how to continue based on the state of
the rwlock. */
futex_wait_simple (&rwlock->__data.__writer_wakeup, waitval,
futex_shared);
/* Get the lock. */
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
/* To start over again, remove the thread from the writer list. */
--rwlock->__data.__nr_writers_queued;
/* Get the rwlock if there is no writer and no reader. */
if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
{
/* Mark self as writer. */
rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
break;
}
}
/* We are done, free the lock. */
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
return result;
}
/* Fast path of acquiring write lock for RWLOCK. */
int
__pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
{
LIBC_PROBE (wrlock_entry, 1, rwlock);
if (ELIDE_LOCK (rwlock->__data.__rwelision,
rwlock->__data.__lock == 0
&& rwlock->__data.__writer == 0
&& rwlock->__data.__nr_readers == 0))
return 0;
/* Make sure we are alone. */
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
/* Get the rwlock if there is no writer and no reader. */
if (__glibc_likely((rwlock->__data.__writer |
rwlock->__data.__nr_readers) == 0))
{
/* Mark self as writer. */
rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
/* We are done, free the lock. */
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
return 0;
}
return __pthread_rwlock_wrlock_slow (rwlock);
}
weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
hidden_def (__pthread_rwlock_wrlock)
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