53 lines
1.8 KiB
C
53 lines
1.8 KiB
C
/*
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* Copyright (c) 2014, 2021 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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* semaphore/sem_timedwait.c
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* Lock a semaphore with a timeout.
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*/
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#include <sys/futex.h>
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#include <errno.h>
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#include <semaphore.h>
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#include <stdbool.h>
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#include <time.h>
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int sem_timedwait(sem_t* restrict sem, const struct timespec* restrict abstime)
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{
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while ( true )
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{
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int old = __atomic_load_n(&sem->value, __ATOMIC_SEQ_CST);
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int new = old != -1 ? old - 1 : -1;
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bool waiting = new == -1;
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if ( waiting )
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__atomic_add_fetch(&sem->waiters, 1, __ATOMIC_SEQ_CST);
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if ( old != new &&
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!__atomic_compare_exchange_n(&sem->value, &old, new, false,
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__ATOMIC_SEQ_CST, __ATOMIC_RELAXED) )
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{
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if ( waiting )
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__atomic_sub_fetch(&sem->waiters, 1, __ATOMIC_SEQ_CST);
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continue;
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}
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if ( !waiting )
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return 0;
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int op = FUTEX_WAIT | FUTEX_ABSOLUTE | FUTEX_CLOCK(CLOCK_REALTIME);
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int ret = futex(&sem->value, op, -1, abstime);
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__atomic_sub_fetch(&sem->waiters, 1, __ATOMIC_SEQ_CST);
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if ( ret < 0 && errno != EAGAIN )
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return -1;
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}
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}
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