score/src/corerwlockobtainread.c

0001 /* SPDX-License-Identifier: BSD-2-Clause */
0002
0003 /**
0004  * @file
0005  *
0006  * @ingroup RTEMSScoreRWLock
0007  *
0008  * @brief This source file contains the implementation of
0009  *   _CORE_RWLock_Seize_for_reading().
0010  */
0011
0012 /*
0013  *  COPYRIGHT (c) 1989-2006.
0014  *  On-Line Applications Research Corporation (OAR).
0015  *
0016  * Redistribution and use in source and binary forms, with or without
0017  * modification, are permitted provided that the following conditions
0018  * are met:
0019  * 1. Redistributions of source code must retain the above copyright
0020  *    notice, this list of conditions and the following disclaimer.
0021  * 2. Redistributions in binary form must reproduce the above copyright
0022  *    notice, this list of conditions and the following disclaimer in the
0023  *    documentation and/or other materials provided with the distribution.
0024  *
0025  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
0026  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
0027  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
0028  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
0029  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
0030  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
0031  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
0032  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
0033  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
0034  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
0035  * POSSIBILITY OF SUCH DAMAGE.
0036  */
0037
0038 #ifdef HAVE_CONFIG_H
0039 #include "config.h"
0040 #endif
0041
0042 #include <rtems/score/corerwlockimpl.h>
0043 #include <rtems/score/threadimpl.h>
0044 #include <rtems/score/threadqimpl.h>
0045 #include <rtems/score/statesimpl.h>
0046 #include <rtems/score/watchdog.h>
0047
0048 Status_Control _CORE_RWLock_Seize_for_reading(
0049   CORE_RWLock_Control  *the_rwlock,
0050   bool                  wait,
0051   Thread_queue_Context *queue_context
0052 )
0053 {
0054   Thread_Control *executing;
0055
0056   /*
0057    *  If unlocked, then OK to read.
0058    *  If locked for reading and no waiters, then OK to read.
0059    *  If any thread is waiting, then we wait.
0060    */
0061
0062   executing = _CORE_RWLock_Acquire( the_rwlock, queue_context );
0063
0064   switch ( the_rwlock->current_state ) {
0065     case CORE_RWLOCK_UNLOCKED:
0066       the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING;
0067       the_rwlock->number_of_readers += 1;
0068       _CORE_RWLock_Release( the_rwlock, queue_context );
0069       return STATUS_SUCCESSFUL;
0070
0071     case CORE_RWLOCK_LOCKED_FOR_READING:
0072       if ( _Thread_queue_Is_empty( &the_rwlock->Queue.Queue ) ) {
0073         the_rwlock->number_of_readers += 1;
0074         _CORE_RWLock_Release( the_rwlock, queue_context );
0075         return STATUS_SUCCESSFUL;
0076       }
0077       break;
0078     case CORE_RWLOCK_LOCKED_FOR_WRITING:
0079       break;
0080   }
0081
0082   /*
0083    *  If the thread is not willing to wait, then return immediately.
0084    */
0085
0086   if ( !wait ) {
0087     _CORE_RWLock_Release( the_rwlock, queue_context );
0088     return STATUS_UNAVAILABLE;
0089   }
0090
0091   /*
0092    *  We need to wait to enter this critical section
0093    */
0094
0095   executing->Wait.option = CORE_RWLOCK_THREAD_WAITING_FOR_READ;
0096
0097   _Thread_queue_Context_set_thread_state(
0098     queue_context,
0099    STATES_WAITING_FOR_RWLOCK
0100   );
0101   _Thread_queue_Enqueue(
0102      &the_rwlock->Queue.Queue,
0103      CORE_RWLOCK_TQ_OPERATIONS,
0104      executing,
0105      queue_context
0106   );
0107   return _Thread_Wait_get_status( executing );
0108 }