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a2f0363f81
This adds new functions for futex operations, starting with wait, abstimed_wait, reltimed_wait, wake. They add documentation and error checking according to the current draft of the Linux kernel futex manpage. Waiting with absolute or relative timeouts is split into separate functions. This allows for removing a few cases of code duplication in pthreads code, which uses absolute timeouts; also, it allows us to put platform-specific code to go from an absolute to a relative timeout into the platform-specific futex abstractions.. Futex operations that can be canceled are also split out into separate functions suffixed by "_cancelable". There are separate versions for both Linux and NaCl; while they currently differ only slightly, my expectation is that the separate versions of lowlevellock-futex.h will eventually be merged into futex-internal.h when we get to move the lll_ functions over to the new futex API.
130 lines
3.8 KiB
C
130 lines
3.8 KiB
C
/* Copyright (C) 2003-2015 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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