101 lines
2.9 KiB
C
101 lines
2.9 KiB
C
/* Copyright (C) 2003-2014 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <sysdep.h>
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#include <lowlevellock.h>
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#include <pthread.h>
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#include <pthreadP.h>
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#include <stap-probe.h>
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/* Acquire read lock for RWLOCK. */
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int
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__pthread_rwlock_rdlock (rwlock)
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pthread_rwlock_t *rwlock;
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{
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int result = 0;
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LIBC_PROBE (rdlock_entry, 1, rwlock);
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/* Make sure we are alone. */
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lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
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while (1)
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{
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/* Get the rwlock if there is no writer... */
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if (rwlock->__data.__writer == 0
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/* ...and if either no writer is waiting or we prefer readers. */
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&& (!rwlock->__data.__nr_writers_queued
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|| PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
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{
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/* Increment the reader counter. Avoid overflow. */
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if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
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{
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/* Overflow on number of readers. */
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--rwlock->__data.__nr_readers;
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result = EAGAIN;
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}
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else
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LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
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break;
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}
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/* Make sure we are not holding the rwlock as a writer. This is
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a deadlock situation we recognize and report. */
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if (__builtin_expect (rwlock->__data.__writer
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== THREAD_GETMEM (THREAD_SELF, tid), 0))
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{
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result = EDEADLK;
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break;
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}
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/* Remember that we are a reader. */
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if (__glibc_unlikely (++rwlock->__data.__nr_readers_queued == 0))
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{
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/* Overflow on number of queued readers. */
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--rwlock->__data.__nr_readers_queued;
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result = EAGAIN;
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break;
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}
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int waitval = rwlock->__data.__readers_wakeup;
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/* Free the lock. */
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lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
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/* Wait for the writer to finish. */
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lll_futex_wait (&rwlock->__data.__readers_wakeup, waitval,
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rwlock->__data.__shared);
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/* Get the lock. */
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lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
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--rwlock->__data.__nr_readers_queued;
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}
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/* We are done, free the lock. */
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lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
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return result;
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}
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weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock)
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hidden_def (__pthread_rwlock_rdlock)
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