posix/src/semtrywait.c

0001 /* SPDX-License-Identifier: BSD-2-Clause */
0002
0003 /**
0004  *  @file
0005  *
0006  *  @brief Lock a Semaphore
0007  *  @ingroup POSIX_SEMAPHORE
0008  */
0009
0010 /*
0011  *  COPYRIGHT (c) 1989-2008.
0012  *  On-Line Applications Research Corporation (OAR).
0013  *
0014  * Redistribution and use in source and binary forms, with or without
0015  * modification, are permitted provided that the following conditions
0016  * are met:
0017  * 1. Redistributions of source code must retain the above copyright
0018  *    notice, this list of conditions and the following disclaimer.
0019  * 2. Redistributions in binary form must reproduce the above copyright
0020  *    notice, this list of conditions and the following disclaimer in the
0021  *    documentation and/or other materials provided with the distribution.
0022  *
0023  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
0024  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
0025  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
0026  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
0027  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
0028  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
0029  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
0030  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
0031  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
0032  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
0033  * POSSIBILITY OF SUCH DAMAGE.
0034  */
0035
0036 #ifdef HAVE_CONFIG_H
0037 #include "config.h"
0038 #endif
0039
0040 #include <rtems/posix/semaphoreimpl.h>
0041
0042 int sem_trywait( sem_t *_sem )
0043 {
0044   Sem_Control          *sem;
0045   Thread_queue_Context  queue_context;
0046   ISR_Level             level;
0047   unsigned int          count;
0048
0049   POSIX_SEMAPHORE_VALIDATE_OBJECT( _sem );
0050
0051   sem = _Sem_Get( &_sem->_Semaphore );
0052   _Thread_queue_Context_initialize( &queue_context );
0053   _Thread_queue_Context_ISR_disable( &queue_context, level );
0054   _Sem_Queue_acquire_critical( sem, &queue_context );
0055
0056   count = sem->count;
0057   if ( RTEMS_PREDICT_TRUE( count > 0 ) ) {
0058     sem->count = count - 1;
0059     _Sem_Queue_release( sem, level, &queue_context );
0060     return 0;
0061   } else {
0062     _Sem_Queue_release( sem, level, &queue_context );
0063     rtems_set_errno_and_return_minus_one( EAGAIN );
0064   }
0065 }