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/*
* -------------------------------------------------------------
*
* Module: sem_trywait.c
*
* Purpose:
* Semaphores aren't actually part of the PThreads standard.
* They are defined by the POSIX Standard:
*
* POSIX 1003.1b-1993 (POSIX.1b)
*
* -------------------------------------------------------------
*
* --------------------------------------------------------------------------
*
* Pthreads4w - POSIX Threads Library for Win32
* Copyright(C) 1998 John E. Bossom
* Copyright(C) 1999-2018, Pthreads4w contributors
*
* Homepage: https://sourceforge.net/projects/pthreads4w/
*
* The current list of contributors is contained
* in the file CONTRIBUTORS included with the source
* code distribution. The list can also be seen at the
* following World Wide Web location:
* https://sourceforge.net/p/pthreads4w/wiki/Contributors/
*
* This file is part of Pthreads4w.
*
* Pthreads4w is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Pthreads4w is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Pthreads4w. If not, see <http://www.gnu.org/licenses/>. *
*/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include "pthread.h"
#include "semaphore.h"
#include "implement.h"
int
sem_trywait (sem_t * sem)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function tries to wait on a semaphore.
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
* DESCRIPTION
* This function tries to wait on a semaphore. If the
* semaphore value is greater than zero, it decreases
* its value by one. If the semaphore value is zero, then
* this function returns immediately with the error EAGAIN
*
* RESULTS
* 0 successfully decreased semaphore,
* -1 failed, error in errno
* ERRNO
* EAGAIN the semaphore was already locked,
* EINVAL 'sem' is not a valid semaphore,
* ENOTSUP sem_trywait is not supported,
* EINTR the function was interrupted by a signal,
* EDEADLK a deadlock condition was detected.
*
* ------------------------------------------------------
*/
{
int result = 0;
sem_t s = *sem;
ptw32_mcs_local_node_t node;
ptw32_mcs_lock_acquire(&s->lock, &node);
if (s->value > 0)
{
s->value--;
}
else
{
result = EAGAIN;
}
ptw32_mcs_lock_release(&node);
if (result != 0)
{
PTW32_SET_ERRNO(result);
return -1;
}
return 0;
} /* sem_trywait */
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