c6b5bcd182
As a follow up to Ibba98f5d88be1c306d14e9b9366302ecbef6d534, where we added a work around to convert the CLOCK_REALTIME timeouts to CLOCK_MONOTONIC for pthread and semaphore timed wait functions, we're introducing a set of _monotonic_np versions of each of these functions that wait on CLOCK_MONOTONIC directly. The primary motivation here is that while the above work around helps for 3rd party code, it creates a dilemma when implementing new code that would use these functions: either one implements code with these functions knowing there is a race condition possible or one avoids these functions and reinvent their own waiting/signaling mechanisms. Neither are satisfactory, so we create a third option to use these Android specific _monotonic_np functions that completely remove the race condition while keeping the rest of the interface. Specifically this adds the below functions: pthread_mutex_timedlock_monotonic_np() pthread_cond_timedwait_monotonic_np() pthread_rwlock_timedrdlock_monotonic_np() pthread_rwlock_timedwrlock_monotonic_np() sem_timedwait_monotonic_np() Note that pthread_cond_timedwait_monotonic_np() previously existed and was removed since it's possible to initialize a condition variable to use CLOCK_MONOTONIC. It is added back for a mix of reasons, 1) Symmetry with the rest of the functions we're adding 2) libc++ cannot easily take advantage of the new initializer, but will be able to use this function in order to wait on std::steady_clock 3) Frankly, it's a better API to specify the clock in the waiter function than to specify the clock when the condition variable is initialized. Bug: 73951740 Test: new unit tests Change-Id: I23aa5c204e36a194237d41e064c5c8ccaa4204e3
69 lines
2.5 KiB
C
69 lines
2.5 KiB
C
/*
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* Copyright (C) 2008 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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#ifndef _SEMAPHORE_H
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#define _SEMAPHORE_H
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#include <sys/cdefs.h>
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__BEGIN_DECLS
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struct timespec;
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typedef struct {
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unsigned int count;
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#ifdef __LP64__
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int __reserved[3];
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#endif
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} sem_t;
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#define SEM_FAILED __BIONIC_CAST(reinterpret_cast, sem_t*, 0)
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int sem_destroy(sem_t* __sem);
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int sem_getvalue(sem_t* __sem, int* __value);
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int sem_init(sem_t* __sem, int __shared, unsigned int __value);
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int sem_post(sem_t* __sem);
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int sem_timedwait(sem_t* __sem, const struct timespec* __ts);
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/*
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* POSIX only supports using sem_timedwait() with CLOCK_REALTIME, however that is typically
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* inappropriate, since that clock can change dramatically, causing the timeout to either
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* expire earlier or much later than intended. This function is added to use a timespec based
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* on CLOCK_MONOTONIC that does not suffer from this issue.
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*/
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int sem_timedwait_monotonic_np(sem_t* __sem, const struct timespec* __ts) __INTRODUCED_IN(28);
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int sem_trywait(sem_t* __sem);
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int sem_wait(sem_t* __sem);
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/* These aren't actually implemented. */
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sem_t* sem_open(const char* __name, int _flags, ...);
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int sem_close(sem_t* __sem);
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int sem_unlink(const char* __name);
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__END_DECLS
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#endif
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