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39 lines
1.4 KiB
C++
39 lines
1.4 KiB
C++
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/*******************************************************************************
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Copyright(C) Jonas 'Sortie' Termansen 2014.
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This file is part of Sortix libpthread.
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Sortix libpthread is free software: you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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Sortix libpthread is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with Sortix libpthread. If not, see <http://www.gnu.org/licenses/>.
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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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extern "C" 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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