source: rtems/cpukit/score/src/corerwlockrelease.c @ bd029d87

/*
 *  SuperCore RWLock Handler -- Release a RWLock
 *
 *  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_Release
 *
 *  This function releases the rwlock.
 *
 *  Input parameters:
 *    the_rwlock    - the rwlock control block to initialize
 *
 *  Output parameters:  NONE
 */

CORE_RWLock_Status _CORE_RWLock_Release(
  CORE_RWLock_Control  *the_rwlock
)
{
  ISR_Level       level;
  Thread_Control *executing = _Thread_Executing;
  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 );
    switch ( the_rwlock->current_state ) {
      case CORE_RWLOCK_UNLOCKED:
        _ISR_Enable( level );
        executing->Wait.return_code = CORE_RWLOCK_UNAVAILABLE;
        return CORE_RWLOCK_SUCCESSFUL;

      case 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;
        }
        executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
        break;
      case CORE_RWLOCK_LOCKED_FOR_WRITING:
        executing->Wait.return_code = CORE_RWLOCK_SUCCESSFUL;
        break;
    }

    /*
     * 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;
}