118 lines
3.5 KiB
C
118 lines
3.5 KiB
C
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/*
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* -------------------------------------------------------------
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*
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* Module: sem_trywait.c
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*
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* Purpose:
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* Semaphores aren't actually part of the PThreads standard.
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* They are defined by the POSIX Standard:
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*
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* POSIX 1003.1b-1993 (POSIX.1b)
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*
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* -------------------------------------------------------------
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*
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* --------------------------------------------------------------------------
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*
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* Pthreads-win32 - POSIX Threads Library for Win32
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* Copyright(C) 1998 John E. Bossom
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* Copyright(C) 1999,2005 Pthreads-win32 contributors
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*
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* Contact Email: rpj@callisto.canberra.edu.au
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*
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* The current list of contributors is contained
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* in the file CONTRIBUTORS included with the source
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* code distribution. The list can also be seen at the
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* following World Wide Web location:
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* http://sources.redhat.com/pthreads-win32/contributors.html
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library in the file COPYING.LIB;
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* if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
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*/
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#include "pthread.h"
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#include "semaphore.h"
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#include "implement.h"
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int
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sem_trywait (sem_t * sem)
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/*
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* ------------------------------------------------------
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* DOCPUBLIC
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* This function tries to wait on a semaphore.
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*
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* PARAMETERS
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* sem
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* pointer to an instance of sem_t
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*
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* DESCRIPTION
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* This function tries to wait on a semaphore. If the
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* semaphore value is greater than zero, it decreases
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* its value by one. If the semaphore value is zero, then
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* this function returns immediately with the error EAGAIN
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*
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* RESULTS
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* 0 successfully decreased semaphore,
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* -1 failed, error in errno
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* ERRNO
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* EAGAIN the semaphore was already locked,
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* EINVAL 'sem' is not a valid semaphore,
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* ENOTSUP sem_trywait is not supported,
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* EINTR the function was interrupted by a signal,
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* EDEADLK a deadlock condition was detected.
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*
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* ------------------------------------------------------
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*/
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{
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int result = 0;
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sem_t s = *sem;
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if (s == NULL)
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{
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result = EINVAL;
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}
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else if ((result = pthread_mutex_lock (&s->lock)) == 0)
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{
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/* See sem_destroy.c
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*/
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if (*sem == NULL)
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{
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(void) pthread_mutex_unlock (&s->lock);
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errno = EINVAL;
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return -1;
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}
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if (s->value > 0)
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{
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s->value--;
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}
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else
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{
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result = EAGAIN;
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}
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(void) pthread_mutex_unlock (&s->lock);
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}
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if (result != 0)
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{
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errno = result;
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return -1;
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}
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return 0;
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} /* sem_trywait */
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