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/**
* @file
*
* @brief Releases the RWLock
*
* @ingroup ScoreRWLock
*/
/*
* 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/system.h>
#include <rtems/score/corerwlockimpl.h>
#include <rtems/score/threadqimpl.h>
#include <rtems/score/watchdog.h>
CORE_RWLock_Status _CORE_RWLock_Release(
CORE_RWLock_Control *the_rwlock,
Thread_Control *executing
)
{
ISR_Level level;
Thread_Control *next;
/*
* 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.
*/
_ISR_Disable( level );
if ( the_rwlock->current_state == CORE_RWLOCK_UNLOCKED){
_ISR_Enable( level );
executing->Wait.return_code = CORE_RWLOCK_UNAVAILABLE;
return CORE_RWLOCK_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 */
_ISR_Enable( level );
return CORE_RWLOCK_SUCCESSFUL;
}
}
/* CORE_RWLOCK_LOCKED_FOR_WRITING or READING with readers */
executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
/*
* Implicitly transition to "unlocked" and find another thread interested
* in obtaining this rwlock.
*/
the_rwlock->current_state = CORE_RWLOCK_UNLOCKED;
_ISR_Enable( level );
next = _Thread_queue_Dequeue( &the_rwlock->Wait_queue );
if ( next ) {
if ( next->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_WRITE ) {
the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_WRITING;
return CORE_RWLOCK_SUCCESSFUL;
}
/*
* Must be CORE_RWLOCK_THREAD_WAITING_FOR_READING
*/
the_rwlock->number_of_readers += 1;
the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING;
/*
* Now see if more readers can be let go.
*/
while ( 1 ) {
next = _Thread_queue_First( &the_rwlock->Wait_queue );
if ( !next ||
next->Wait.option == CORE_RWLOCK_THREAD_WAITING_FOR_WRITE )
return CORE_RWLOCK_SUCCESSFUL;
the_rwlock->number_of_readers += 1;
_Thread_queue_Extract( &the_rwlock->Wait_queue, next );
}
}
/* indentation is to match _ISR_Disable at top */
return CORE_RWLOCK_SUCCESSFUL;
}
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