47 lines
1.7 KiB
C
47 lines
1.7 KiB
C
/*
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* Copyright (c) 2013, 2014, 2021, 2022 Jonas 'Sortie' Termansen.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* pthread/pthread_mutex_unlock.c
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* Unlocks a mutex.
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*/
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#include <sys/futex.h>
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#include <limits.h>
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#include <pthread.h>
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#include <stdbool.h>
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static const int UNLOCKED = 0;
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static const int CONTENDED = 2;
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int pthread_mutex_unlock(pthread_mutex_t* mutex)
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{
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if ( mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->recursion )
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{
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mutex->recursion--;
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return 0;
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}
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mutex->owner = 0;
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// TODO: Multiple threads could have caused the contention and this wakes
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// only one such thread, but then the mutex returns to normal and the
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// subsequent unlocks doesn't wake the other contended threads. Work
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// around this bug by waking all of them instead, but it's better to
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// instead count the number of waiting threads.
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if ( __atomic_exchange_n(&mutex->lock, UNLOCKED,
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__ATOMIC_SEQ_CST) == CONTENDED )
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futex(&mutex->lock, FUTEX_WAKE, INT_MAX, NULL);
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return 0;
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}
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