35 lines
1.2 KiB
C
35 lines
1.2 KiB
C
/*
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* Copyright (c) 2014 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_trywait.c
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* Lock a semaphore.
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*/
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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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int sem_trywait(sem_t* sem)
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{
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int old_value = __atomic_load_n(&sem->value, __ATOMIC_SEQ_CST);
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if ( old_value <= 0 )
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return errno = EAGAIN, -1;
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int new_value = old_value - 1;
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if ( !__atomic_compare_exchange_n(&sem->value, &old_value, new_value, false,
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__ATOMIC_SEQ_CST, __ATOMIC_RELAXED) )
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return errno = EAGAIN, -1;
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return 0;
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}
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