Remove possibility of delivery race conditions ---------------------------------------------- Key: JBMESSAGING-355 URL: http://jira.jboss.com/jira/browse/JBMESSAGING-355 Project: JBoss Messaging Issue Type: Task Reporter: Tim Fox Assigned To: Tim Fox Fix For: 1.0.2.CR1 Attachments: race-condition.log Original Estimate: 3 days Remaining Estimate: 3 days Currently race conditions can occur on message delivery where the delivery is acknowledged or cancelled before the call to handle has returned. In ChannelState we defensively program against this by synchronizing on the returned delivery and by dealing with the situation where the delivery does not exist in the channel state and ignoring. See ChannelSupport::deliver() and ChannelState.cancelDelivery. This approach has the following problems: Complexity of code to maintain and understand. Where acks return quickly we are likely to get contention on the lock in ChannelSupport::deliver, thus reducing throughput. A much simpler solution enables us to remove the possibility of such race conditions and remove the corresponding lock contention. This can be done by adding a confirm() method on Delivery. When the receiver receives the message in it's handle() call, before dispatching the message it calls Delivery::confirm. This results in the channel adding the delivery to the channel state. Thus we can be assured that the delivery exists before any acknowledgment or cancellation comes in. This is a very simple change.