From c654b52517c2d255aa98eed347edeba60dc854d0 Mon Sep 17 00:00:00 2001 From: Sebastian Huber Date: Thu, 30 Apr 2015 13:18:45 +0200 Subject: score: Delete _CORE_message_queue_Flush_support() Check the number of pending messages in _CORE_message_queue_Flush() to avoid race conditions. --- cpukit/score/src/coremsgflush.c | 72 ++++++++++++++++++++++++++++++++++------- 1 file changed, 60 insertions(+), 12 deletions(-) (limited to 'cpukit/score/src/coremsgflush.c') 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 -#include -#include #include -#include -#include +#include 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; } -- cgit v1.2.3