score: Delete _CORE_message_queue_Flush_support()

Check the number of pending messages in _CORE_message_queue_Flush() to
avoid race conditions.

1 files changed, 60 insertions, 12 deletions

diff --git a/cpukit/score/src/coremsgflush.c b/cpukit/score/src/coremsgflush.c
index 51f6c8db98..05683f0327 100644
--- a/cpukit/score/src/coremsgflush.c
+++ b/cpukit/score/src/coremsgflush.c
@@ -1,8 +1,9 @@
 /**
- *  @file
+ * @file
  *
- *  @brief Flush Pending Messages
- *  @ingroup ScoreMessageQueue
+ * @brief Flush Messages Routine
+ *
+ * @ingroup ScoreMessageQueue
  */
 
 /*
@@ -18,19 +19,66 @@
 #include "config.h"
 #endif
 
-#include <rtems/system.h>
-#include <rtems/score/chain.h>
-#include <rtems/score/isr.h>
 #include <rtems/score/coremsgimpl.h>
-#include <rtems/score/thread.h>
-#include <rtems/score/wkspace.h>
+#include <rtems/score/isr.h>
 
 uint32_t   _CORE_message_queue_Flush(
   CORE_message_queue_Control *the_message_queue
 )
 {
-  if ( the_message_queue->number_of_pending_messages != 0 )
-    return _CORE_message_queue_Flush_support( the_message_queue );
-  else
-    return 0;
+  ISR_Level   level;
+  Chain_Node *inactive_head;
+  Chain_Node *inactive_first;
+  Chain_Node *message_queue_first;
+  Chain_Node *message_queue_last;
+  uint32_t    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 );
+
+  count = the_message_queue->number_of_pending_messages;
+  if ( count != 0 ) {
+    the_message_queue->number_of_pending_messages = 0;
+
+    inactive_head = _Chain_Head( &the_message_queue->Inactive_messages );
+    inactive_first = inactive_head->next;
+    message_queue_first = _Chain_First( &the_message_queue->Pending_messages );
+    message_queue_last = _Chain_Last( &the_message_queue->Pending_messages );
+
+    inactive_head->next = message_queue_first;
+    message_queue_last->next = inactive_first;
+    inactive_first->previous = message_queue_last;
+    message_queue_first->previous = inactive_head;
+
+    _Chain_Initialize_empty( &the_message_queue->Pending_messages );
+  }
+
+  _ISR_Enable( level );
+  return count;
 }