ac49cedc7e
pthread's and semaphore's default behavior is to use CLOCK_REALTIME,
however this behavior is essentially never intended, as that clock is
prone to change discontinuously.
What users really intend is to use CLOCK_MONOTONIC, however only
pthread_cond_timedwait() provides this as an option and even there, a
large amount of existing code does not opt into CLOCK_MONOTONIC.
We have seen numerous bugs directly attributable to this difference.
Therefore, we provide this general workaround to always use
CLOCK_MONOTONIC for waiting, regardless of what the input timespec
is.
Specifically this impacts the below APIs:
pthread_mutex_timedlock()
pthread_cond_timedwait()
pthread_rwlock_timedrdlock()
pthread_rwlock_timedwrlock()
sem_timedwait()
Test: boot bullhead, boot sailfish
Test: bionic pthread/semaphore unit tests
Test: check that pthread_cond_timedwait() timeouts are uneffected by
CLOCK_REALTIME time changes
Bug: 64694413
Bug: 64623895
Bug: 35756266
Bug: 35678943
Change-Id: Ibba98f5d88be1c306d14e9b9366302ecbef6d534
59 lines
2.7 KiB
C++
59 lines
2.7 KiB
C++
/*
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* Copyright (C) 2017 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "private/bionic_futex.h"
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#include <time.h>
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#include "private/bionic_time_conversions.h"
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int __futex_wait_ex(volatile void* ftx, bool shared, int value, bool use_realtime_clock,
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const timespec* abs_timeout) {
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const timespec* futex_abs_timeout = abs_timeout;
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// pthread's and semaphore's default behavior is to use CLOCK_REALTIME, however this behavior is
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// essentially never intended, as that clock is prone to change discontinuously.
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//
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// What users really intend is to use CLOCK_MONOTONIC, however only pthread_cond_timedwait()
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// provides this as an option and even there, a large amount of existing code does not opt into
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// CLOCK_MONOTONIC.
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//
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// We have seen numerous bugs directly attributable to this difference. Therefore, we provide
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// this general workaround to always use CLOCK_MONOTONIC for waiting, regardless of what the input
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// timespec is.
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timespec converted_monotonic_abs_timeout;
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if (abs_timeout && use_realtime_clock) {
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monotonic_time_from_realtime_time(converted_monotonic_abs_timeout, *abs_timeout);
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if (converted_monotonic_abs_timeout.tv_sec < 0) {
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return -ETIMEDOUT;
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}
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futex_abs_timeout = &converted_monotonic_abs_timeout;
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}
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return __futex(ftx, (shared ? FUTEX_WAIT_BITSET : FUTEX_WAIT_BITSET_PRIVATE), value,
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futex_abs_timeout, FUTEX_BITSET_MATCH_ANY);
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}
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