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130 lines
3.8 KiB
C
130 lines
3.8 KiB
C
/* Copyright (C) 2003-2016 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 <futex-internal.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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#include <elide.h>
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/* Acquire write lock for RWLOCK. */
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static int __attribute__((noinline))
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__pthread_rwlock_wrlock_slow (pthread_rwlock_t *rwlock)
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{
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int result = 0;
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int futex_shared =
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rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
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/* Caller has taken the lock. */
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while (1)
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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 writer. */
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if (++rwlock->__data.__nr_writers_queued == 0)
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{
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/* Overflow on number of queued writers. */
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--rwlock->__data.__nr_writers_queued;
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result = EAGAIN;
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break;
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}
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int waitval = rwlock->__data.__writer_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 or reader(s) to finish. We do not check the
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return value because we decide how to continue based on the state of
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the rwlock. */
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futex_wait_simple (&rwlock->__data.__writer_wakeup, waitval,
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futex_shared);
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/* Get the lock. */
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lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
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/* To start over again, remove the thread from the writer list. */
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--rwlock->__data.__nr_writers_queued;
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/* Get the rwlock if there is no writer and no reader. */
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if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
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{
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/* Mark self as writer. */
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rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
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LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
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break;
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}
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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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/* Fast path of acquiring write lock for RWLOCK. */
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int
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__pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
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{
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LIBC_PROBE (wrlock_entry, 1, rwlock);
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if (ELIDE_LOCK (rwlock->__data.__rwelision,
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rwlock->__data.__lock == 0
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&& rwlock->__data.__writer == 0
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&& rwlock->__data.__nr_readers == 0))
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return 0;
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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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/* Get the rwlock if there is no writer and no reader. */
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if (__glibc_likely((rwlock->__data.__writer |
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rwlock->__data.__nr_readers) == 0))
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{
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/* Mark self as writer. */
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rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
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LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
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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 0;
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}
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return __pthread_rwlock_wrlock_slow (rwlock);
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}
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weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
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hidden_def (__pthread_rwlock_wrlock)
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