path: root/cpukit/score/src/corerwlockobtainread.c

/**
 * @file 
 * 
 * @brief Obtain RWLock for reading
 * @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/score/corerwlockimpl.h>
#include <rtems/score/threadqimpl.h>
#include <rtems/score/statesimpl.h>
#include <rtems/score/watchdog.h>

void _CORE_RWLock_Obtain_for_reading(
  CORE_RWLock_Control                 *the_rwlock,
  Thread_Control                      *executing,
  Objects_Id                           id,
  bool                                 wait,
  Watchdog_Interval                    timeout,
  CORE_RWLock_API_mp_support_callout   api_rwlock_mp_support
)
{
  ISR_lock_Context lock_context;

  /*
   *  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.
   */

  _Thread_queue_Acquire( &the_rwlock->Wait_queue, &lock_context );
    switch ( the_rwlock->current_state ) {
      case CORE_RWLOCK_UNLOCKED:
	the_rwlock->current_state = CORE_RWLOCK_LOCKED_FOR_READING;
	the_rwlock->number_of_readers += 1;
	_Thread_queue_Release( &the_rwlock->Wait_queue, &lock_context );
	executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
	return;

      case CORE_RWLOCK_LOCKED_FOR_READING: {
        Thread_Control *waiter;
        waiter = _Thread_queue_First_locked( &the_rwlock->Wait_queue );
        if ( !waiter ) {
	  the_rwlock->number_of_readers += 1;
	  _Thread_queue_Release( &the_rwlock->Wait_queue, &lock_context );
	  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 ) {
      _Thread_queue_Release( &the_rwlock->Wait_queue, &lock_context );
      executing->Wait.return_code = CORE_RWLOCK_UNAVAILABLE;
      return;
    }

    /*
     *  We need to wait to enter this critical section
     */

    executing->Wait.id          = id;
    executing->Wait.option      = CORE_RWLOCK_THREAD_WAITING_FOR_READ;
    executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;

    _Thread_queue_Enqueue_critical(
       &the_rwlock->Wait_queue.Queue,
       the_rwlock->Wait_queue.operations,
       executing,
       STATES_WAITING_FOR_RWLOCK,
       timeout,
       CORE_RWLOCK_TIMEOUT,
       &lock_context
    );

    /* return to API level so it can dispatch and we block */
}