/*
* -------------------------------------------------------------
*
* 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)
*
* -------------------------------------------------------------
*
* --------------------------------------------------------------------------
*
* Pthreads-win32 - POSIX Threads Library for Win32
* Copyright(C) 1998 John E. Bossom
* Copyright(C) 1999,2005 Pthreads-win32 contributors
*
* Contact Email: rpj@callisto.canberra.edu.au
*
* 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:
* http://sources.redhat.com/pthreads-win32/contributors.html
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library in the file COPYING.LIB;
* if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#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;
if (s == NULL)
{
result = EINVAL;
}
else if ((result = pthread_mutex_lock (&s->lock)) == 0)
{
/* See sem_destroy.c
*/
if (*sem == NULL)
{
(void) pthread_mutex_unlock (&s->lock);
errno = EINVAL;
return -1;
}
if (s->value > 0)
{
s->value--;
}
else
{
result = EAGAIN;
}
(void) pthread_mutex_unlock (&s->lock);
}
if (result != 0)
{
errno = result;
return -1;
}
return 0;
} /* sem_trywait */