mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-22 19:00:07 +00:00
96 lines
2.9 KiB
C
96 lines
2.9 KiB
C
/* Copyright (C) 2003,2004,2007,2011 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 <pthread.h>
|
|
#include <pthreadP.h>
|
|
|
|
|
|
/* Acquire read lock for RWLOCK. */
|
|
int
|
|
__pthread_rwlock_rdlock (rwlock)
|
|
pthread_rwlock_t *rwlock;
|
|
{
|
|
int result = 0;
|
|
|
|
/* Make sure we are alone. */
|
|
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
while (1)
|
|
{
|
|
/* Get the rwlock if there is no writer... */
|
|
if (rwlock->__data.__writer == 0
|
|
/* ...and if either no writer is waiting or we prefer readers. */
|
|
&& (!rwlock->__data.__nr_writers_queued
|
|
|| PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
|
|
{
|
|
/* Increment the reader counter. Avoid overflow. */
|
|
if (__builtin_expect (++rwlock->__data.__nr_readers == 0, 0))
|
|
{
|
|
/* Overflow on number of readers. */
|
|
--rwlock->__data.__nr_readers;
|
|
result = EAGAIN;
|
|
}
|
|
|
|
break;
|
|
}
|
|
|
|
/* 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 reader. */
|
|
if (__builtin_expect (++rwlock->__data.__nr_readers_queued == 0, 0))
|
|
{
|
|
/* Overflow on number of queued readers. */
|
|
--rwlock->__data.__nr_readers_queued;
|
|
result = EAGAIN;
|
|
break;
|
|
}
|
|
|
|
int waitval = rwlock->__data.__readers_wakeup;
|
|
|
|
/* Free the lock. */
|
|
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
/* Wait for the writer to finish. */
|
|
lll_futex_wait (&rwlock->__data.__readers_wakeup, waitval,
|
|
rwlock->__data.__shared);
|
|
|
|
/* Get the lock. */
|
|
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
--rwlock->__data.__nr_readers_queued;
|
|
}
|
|
|
|
/* We are done, free the lock. */
|
|
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
return result;
|
|
}
|
|
|
|
weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock)
|
|
strong_alias (__pthread_rwlock_rdlock, __pthread_rwlock_rdlock_internal)
|