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- /* Copyright (C) 2003, 2004, 2007 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
- attribute_protected
- __pthread_rwlock_rdlock (
- pthread_rwlock_t *rwlock)
- {
- int result = 0;
- /* Make sure we are along. */
- 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)
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