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/*

 *  CORE Message Queue Handler

 *

 *  DESCRIPTION:

 *

 *  This package is the implementation of the CORE Message Queue Handler.

 *  This core object provides task synchronization and communication functions

 *  via messages passed to queue objects.

 *

 *  COPYRIGHT (c) 1989-1999.

 *  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.OARcorp.com/rtems/license.html.

 *

 *  $Id: coremsgflushsupp.c,v 1.2 2001-09-27 11:59:34 chris Exp $

 */

#include <rtems/system.h>

#include <rtems/score/chain.h>

#include <rtems/score/isr.h>

#include <rtems/score/object.h>

#include <rtems/score/coremsg.h>

#include <rtems/score/states.h>

#include <rtems/score/thread.h>

#include <rtems/score/wkspace.h>

#if defined(RTEMS_MULTIPROCESSING)

#include <rtems/score/mpci.h>

#endif

/*PAGE

 *

 *  _CORE_message_queue_Flush_support

 *

 *  This message handler routine removes all messages from a message queue

 *  and returns them to the inactive message pool.  The number of messages

 *  flushed from the queue is returned

 *

 *  Input parameters:

 *    the_message_queue - pointer to message queue

 *

 *  Output parameters:

 *    returns - number of messages placed on inactive chain

 *

 *  INTERRUPT LATENCY:

 *    only case

 */

unsigned32 _CORE_message_queue_Flush_support(

  CORE_message_queue_Control *the_message_queue

)

{

  ISR_Level   level;

  Chain_Node *inactive_first;

  Chain_Node *message_queue_first;

  Chain_Node *message_queue_last;

  unsigned32  count;

  /*

   *  Currently, RTEMS supports no API that has both flush and blocking

   *  sends.  Thus, this routine assumes that there are no senders

   *  blocked waiting to send messages.  In the event, that an API is

   *  added that can flush a message queue when threads are blocked

   *  waiting to send, there are two basic behaviors envisioned:

   *

   *  (1) The thread queue of pending senders is a logical extension

   *  of the pending message queue.  In this case, it should be

   *  flushed using the _Thread_queue_Flush() service with a status

   *  such as CORE_MESSAGE_QUEUE_SENDER_FLUSHED (which currently does

   *  not exist).  This can be implemented without changing the "big-O"

   *  of the message flushing part of the routine.

   *

   *  (2) Only the actual messages queued should be purged.  In this case,

   *  the blocked sender threads must be allowed to send their messages.

   *  In this case, the implementation will be forced to individually

   *  dequeue the senders and queue their messages.  This will force

   *  this routine to have "big O(n)" where n is the number of blocked

   *  senders.  If there are more messages pending than senders blocked,

   *  then the existing flush code can be used to dispose of the remaining

   *  pending messages.

   *

   *  For now, though, we are very happy to have a small routine with

   *  fixed execution time that only deals with pending messages.

   */

  _ISR_Disable( level );

    inactive_first      = the_message_queue->Inactive_messages.first;

    message_queue_first = the_message_queue->Pending_messages.first;

    message_queue_last  = the_message_queue->Pending_messages.last;

    the_message_queue->Inactive_messages.first = message_queue_first;

    message_queue_last->next = inactive_first;

    inactive_first->previous = message_queue_last;

    message_queue_first->previous          =

               _Chain_Head( &the_message_queue->Inactive_messages );

    _Chain_Initialize_empty( &the_message_queue->Pending_messages );

    count = the_message_queue->number_of_pending_messages;

    the_message_queue->number_of_pending_messages = 0;

  _ISR_Enable( level );

  return count;

}