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8491ed6d70
This patch relies on the C version of the rwlocks posted earlier. With C rwlocks it is very straight forward to do adaptive elision using TSX. It is based on the infrastructure added earlier for mutexes, but uses its own elision macros. The macros are fairly general purpose and could be used for other elision purposes too. This version is much cleaner than the earlier assembler based version, and in particular implements adaptation which makes it safer. I changed the behavior slightly to not require any changes in the test suite and fully conform to all expected behaviors (generally at the cost of not eliding in various situations). In particular this means the timedlock variants are not elided. Nested trylock aborts.
142 lines
4.0 KiB
C
142 lines
4.0 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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#include <elide.h>
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/* Acquire read lock for RWLOCK. Slow path. */
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static int __attribute__((noinline))
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__pthread_rwlock_rdlock_slow (pthread_rwlock_t *rwlock)
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{
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int result = 0;
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/* Lock is taken in caller. */
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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 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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/* 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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}
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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 read lock on RWLOCK. */
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int
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__pthread_rwlock_rdlock (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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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... */
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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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/* 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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return __pthread_rwlock_rdlock_slow (rwlock);
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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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