score/src/corerwlockrelease.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_Surrender().
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/assert.h>
0044
0045 static bool _CORE_RWLock_Is_waiting_for_reading(
0046   const Thread_Control *the_thread
0047 )
0048 {
0049   if ( the_thread->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_READ ) {
0050     return true;
0051   } else {
0052     _Assert( the_thread->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_WRITE );
0053     return false;
0054   }
0055 }
0056
0057 static Thread_Control *_CORE_RWLock_Flush_filter(
0058   Thread_Control       *the_thread,
0059   Thread_queue_Queue   *queue,
0060   Thread_queue_Context *queue_context
0061 )
0062 {
0063   CORE_RWLock_Control *the_rwlock;
0064
0065   the_rwlock = RTEMS_CONTAINER_OF(
0066     queue,
0067     CORE_RWLock_Control,
0068     Queue.Queue
0069   );
0070
0071   switch ( the_rwlock->current_state ) {
0072     case CORE_RWLOCK_LOCKED_FOR_READING:
0073       if ( _CORE_RWLock_Is_waiting_for_reading( the_thread ) ) {
0074         the_rwlock->number_of_readers += 1;
0075       } else {
0076         the_thread = NULL;
0077       }
0078       break;
0079     case CORE_RWLOCK_LOCKED_FOR_WRITING:
0080       the_thread = NULL;
0081       break;
0082     default:
0083       _Assert( the_rwlock->current_state == CORE_RWLOCK_UNLOCKED );
0084       if ( _CORE_RWLock_Is_waiting_for_reading( the_thread ) ) {
0085         the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING;
0086         the_rwlock->number_of_readers = 1;
0087       } else {
0088         the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_WRITING;
0089       }
0090       break;
0091   }
0092
0093   return the_thread;
0094 }
0095
0096 Status_Control _CORE_RWLock_Surrender( CORE_RWLock_Control *the_rwlock )
0097 {
0098   Thread_queue_Context queue_context;
0099
0100   /*
0101    *  If unlocked, then OK to read.
0102    *  Otherwise, we have to block.
0103    *  If locked for reading and no waiters, then OK to read.
0104    *  If any thread is waiting, then we wait.
0105    */
0106
0107   _Thread_queue_Context_initialize( &queue_context );
0108   _CORE_RWLock_Acquire( the_rwlock, &queue_context );
0109
0110   if ( the_rwlock->current_state == CORE_RWLOCK_UNLOCKED){
0111     /* This is an error at the caller site */
0112     _CORE_RWLock_Release( the_rwlock, &queue_context );
0113     return STATUS_SUCCESSFUL;
0114   }
0115
0116   if ( the_rwlock->current_state == CORE_RWLOCK_LOCKED_FOR_READING ) {
0117     the_rwlock->number_of_readers -= 1;
0118
0119     if ( the_rwlock->number_of_readers != 0 ) {
0120       /* must be unlocked again */
0121       _CORE_RWLock_Release( the_rwlock, &queue_context );
0122       return STATUS_SUCCESSFUL;
0123     }
0124   }
0125
0126   _Assert(
0127     the_rwlock->current_state == CORE_RWLOCK_LOCKED_FOR_WRITING
0128       || ( the_rwlock->current_state == CORE_RWLOCK_LOCKED_FOR_READING
0129         && the_rwlock->number_of_readers == 0 )
0130   );
0131
0132   /*
0133    * Implicitly transition to "unlocked" and find another thread interested
0134    * in obtaining this rwlock.
0135    */
0136   the_rwlock->current_state = CORE_RWLOCK_UNLOCKED;
0137
0138   _Thread_queue_Flush_critical(
0139     &the_rwlock->Queue.Queue,
0140     CORE_RWLOCK_TQ_OPERATIONS,
0141     _CORE_RWLock_Flush_filter,
0142     &queue_context
0143   );
0144   return STATUS_SUCCESSFUL;
0145 }