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/*
* SuperCore RWLock Handler -- Obtain RWLock for reading
*
* 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.com/license/LICENSE.
*
* $Id$
*/
#if HAVE_CONFIG_H
#include "config.h"
#endif
#include <rtems/system.h>
#include <rtems/score/corerwlock.h>
#include <rtems/score/states.h>
#include <rtems/score/thread.h>
#include <rtems/score/watchdog.h>
/*PAGE
*
* _CORE_rwlock_Obtain_for_reading
*
* This function waits for the rwlock to become available. Optionally,
* a limit may be placed on the duration of the spin.
*
* Input parameters:
* the_rwlock - the rwlock control block to initialize
* timeout_allowed - true if timeout allowed
* timeout - the maximum number of ticks to spin
*
* Output parameters: NONE
*/
void _CORE_RWLock_Obtain_for_reading(
CORE_RWLock_Control *the_rwlock,
Objects_Id id,
bool wait,
Watchdog_Interval timeout,
CORE_RWLock_API_mp_support_callout api_rwlock_mp_support
)
{
ISR_Level level;
Thread_Control *executing = _Thread_Executing;
/*
* If unlocked, then OK to read.
* If locked for reading and no waiters, then OK to read.
* If any thread is waiting, then we wait.
*/
_ISR_Disable( level );
switch ( the_rwlock->current_state ) {
case CORE_RWLOCK_UNLOCKED:
the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING;
the_rwlock->number_of_readers += 1;
_ISR_Enable( level );
executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
return;
case CORE_RWLOCK_LOCKED_FOR_READING: {
Thread_Control *waiter;
waiter = _Thread_queue_First( &the_rwlock->Wait_queue );
if ( !waiter ) {
the_rwlock->number_of_readers += 1;
_ISR_Enable( level );
executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
return;
}
break;
}
case CORE_RWLOCK_LOCKED_FOR_WRITING:
break;
}
/*
* If the thread is not willing to wait, then return immediately.
*/
if ( !wait ) {
_ISR_Enable( level );
executing->Wait.return_code = CORE_RWLOCK_UNAVAILABLE;
return;
}
/*
* We need to wait to enter this critical section
*/
_Thread_queue_Enter_critical_section( &the_rwlock->Wait_queue );
executing->Wait.queue = &the_rwlock->Wait_queue;
executing->Wait.id = id;
executing->Wait.option = CORE_RWLOCK_THREAD_WAITING_FOR_READ;
executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
_ISR_Enable( level );
_Thread_queue_Enqueue_with_handler(
&the_rwlock->Wait_queue,
timeout,
_CORE_RWLock_Timeout
);
/* return to API level so it can dispatch and we block */
}
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