source: rtems/cpukit/score/src/coremsgflushsupp.c @ a85d8ec

4.104.114.84.95
Last change on this file since a85d8ec was 9c1c778d, checked in by Jennifer Averett <Jennifer.Averett@…>, on 01/13/00 at 18:32:38

+ Added comments

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File size: 3.6 KB
Line 
1/*
2 *  CORE Message Queue Handler
3 *
4 *  DESCRIPTION:
5 *
6 *  This package is the implementation of the CORE Message Queue Handler.
7 *  This core object provides task synchronization and communication functions
8 *  via messages passed to queue objects.
9 *
10 *  COPYRIGHT (c) 1989-1999.
11 *  On-Line Applications Research Corporation (OAR).
12 *
13 *  The license and distribution terms for this file may be
14 *  found in the file LICENSE in this distribution or at
15 *  http://www.OARcorp.com/rtems/license.html.
16 *
17 *  $Id$
18 */
19
20#include <rtems/system.h>
21#include <rtems/score/chain.h>
22#include <rtems/score/isr.h>
23#include <rtems/score/object.h>
24#include <rtems/score/coremsg.h>
25#include <rtems/score/states.h>
26#include <rtems/score/thread.h>
27#include <rtems/score/wkspace.h>
28#if defined(RTEMS_MULTIPROCESSING)
29#include <rtems/score/mpci.h>
30#endif
31
32/*PAGE
33 *
34 *  _CORE_message_queue_Flush_support
35 *
36 *  This message handler routine removes all messages from a message queue
37 *  and returns them to the inactive message pool.  The number of messages
38 *  flushed from the queue is returned
39 *
40 *  Input parameters:
41 *    the_message_queue - pointer to message queue
42 *
43 *  Output parameters:
44 *    returns - number of messages placed on inactive chain
45 *
46 *  INTERRUPT LATENCY:
47 *    only case
48 */
49
50unsigned32 _CORE_message_queue_Flush_support(
51  CORE_message_queue_Control *the_message_queue
52)
53{
54  ISR_Level   level;
55  Chain_Node *inactive_first;
56  Chain_Node *message_queue_first;
57  Chain_Node *message_queue_last;
58  unsigned32  count;
59
60  /*
61   *  Currently, RTEMS supports no API that has both flush and blocking
62   *  sends.  Thus, this routine assumes that there are no senders
63   *  blocked waiting to send messages.  In the event, that an API is
64   *  added that can flush a message queue when threads are blocked
65   *  waiting to send, there are two basic behaviors envisioned:
66   *
67   *  (1) The thread queue of pending senders is a logical extension
68   *  of the pending message queue.  In this case, it should be
69   *  flushed using the _Thread_queue_Flush() service with a status
70   *  such as CORE_MESSAGE_QUEUE_SENDER_FLUSHED (which currently does
71   *  not exist).  This can be implemented without changing the "big-O"
72   *  of the message flushing part of the routine.
73   *
74   *  (2) Only the actual messages queued should be purged.  In this case,
75   *  the blocked sender threads must be allowed to send their messages.
76   *  In this case, the implementation will be forced to individually
77   *  dequeue the senders and queue their messages.  This will force
78   *  this routine to have "big O(n)" where n is the number of blocked
79   *  senders.  If there are more messages pending than senders blocked,
80   *  then the existing flush code can be used to dispose of the remaining
81   *  pending messages.
82   *
83   *  For now, though, we are very happy to have a small routine with
84   *  fixed execution time that only deals with pending messages.
85   */
86
87  _ISR_Disable( level );
88    inactive_first      = the_message_queue->Inactive_messages.first;
89    message_queue_first = the_message_queue->Pending_messages.first;
90    message_queue_last  = the_message_queue->Pending_messages.last;
91
92    the_message_queue->Inactive_messages.first = message_queue_first;
93    message_queue_last->next = inactive_first;
94    inactive_first->previous = message_queue_last;
95    message_queue_first->previous          =
96               _Chain_Head( &the_message_queue->Inactive_messages );
97
98    _Chain_Initialize_empty( &the_message_queue->Pending_messages );
99
100    count = the_message_queue->number_of_pending_messages;
101    the_message_queue->number_of_pending_messages = 0;
102  _ISR_Enable( level );
103  return count;
104}
105
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