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/**
* @file
*
* @brief Releases the RWLock
*
* @ingroup RTEMSScoreRWLock
*/
/*
* COPYRIGHT (c) 1989-2006.
* On-Line Applications Research Corporation (OAR).
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
#if HAVE_CONFIG_H
#include "config.h"
#endif
#include <rtems/score/corerwlockimpl.h>
#include <rtems/score/assert.h>
static bool _CORE_RWLock_Is_waiting_for_reading(
const Thread_Control *the_thread
)
{
if ( the_thread->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_READ ) {
return true;
} else {
_Assert( the_thread->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_WRITE );
return false;
}
}
static Thread_Control *_CORE_RWLock_Flush_filter(
Thread_Control *the_thread,
Thread_queue_Queue *queue,
Thread_queue_Context *queue_context
)
{
CORE_RWLock_Control *the_rwlock;
the_rwlock = RTEMS_CONTAINER_OF(
queue,
CORE_RWLock_Control,
Queue.Queue
);
switch ( the_rwlock->current_state ) {
case CORE_RWLOCK_LOCKED_FOR_READING:
if ( _CORE_RWLock_Is_waiting_for_reading( the_thread ) ) {
the_rwlock->number_of_readers += 1;
} else {
the_thread = NULL;
}
break;
case CORE_RWLOCK_LOCKED_FOR_WRITING:
the_thread = NULL;
break;
default:
_Assert( the_rwlock->current_state == CORE_RWLOCK_UNLOCKED );
if ( _CORE_RWLock_Is_waiting_for_reading( the_thread ) ) {
the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING;
the_rwlock->number_of_readers = 1;
} else {
the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_WRITING;
}
break;
}
return the_thread;
}
Status_Control _CORE_RWLock_Surrender( CORE_RWLock_Control *the_rwlock )
{
Thread_queue_Context queue_context;
/*
* If unlocked, then OK to read.
* Otherwise, we have to block.
* If locked for reading and no waiters, then OK to read.
* If any thread is waiting, then we wait.
*/
_Thread_queue_Context_initialize( &queue_context );
_CORE_RWLock_Acquire( the_rwlock, &queue_context );
if ( the_rwlock->current_state == CORE_RWLOCK_UNLOCKED){
/* This is an error at the caller site */
_CORE_RWLock_Release( the_rwlock, &queue_context );
return STATUS_SUCCESSFUL;
}
if ( the_rwlock->current_state == CORE_RWLOCK_LOCKED_FOR_READING ) {
the_rwlock->number_of_readers -= 1;
if ( the_rwlock->number_of_readers != 0 ) {
/* must be unlocked again */
_CORE_RWLock_Release( the_rwlock, &queue_context );
return STATUS_SUCCESSFUL;
}
}
_Assert(
the_rwlock->current_state == CORE_RWLOCK_LOCKED_FOR_WRITING
|| ( the_rwlock->current_state == CORE_RWLOCK_LOCKED_FOR_READING
&& the_rwlock->number_of_readers == 0 )
);
/*
* Implicitly transition to "unlocked" and find another thread interested
* in obtaining this rwlock.
*/
the_rwlock->current_state = CORE_RWLOCK_UNLOCKED;
_Thread_queue_Flush_critical(
&the_rwlock->Queue.Queue,
CORE_RWLOCK_TQ_OPERATIONS,
_CORE_RWLock_Flush_filter,
&queue_context
);
return STATUS_SUCCESSFUL;
}
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