[jboss-jira] [JBoss JIRA] Closed: (JBAS-5228) Race condition maintaining acknowledgements when pushing messages to the client

Race condition maintaining acknowledgements when pushing messages to the client ------------------------------------------------------------------------------- Key: JBAS-5228 URL: http://jira.jboss.com/jira/browse/JBAS-5228 Project: JBoss Application Server Issue Type: Bug Security Level: Public(Everyone can see) Components: JMS service Affects Versions: JBossAS-4.2.2.GA Reporter: Adrian Brock Assigned To: Adrian Brock Fix For: JBossAS-5.0.0.CR1, JBossAS-4.2.3.GA There is a race condition when maintaining/checking message acknowledgements for a subscription when messages are pushed to the client. i.e. when the client asks for a message and there are none, the client is registered as wanting a message and when a message arrives, the message is sent to the client. This involves maintaining a "list" of unacknowledged messages for that client/subscription which must be checked before we allow removal of the the subscription during close. However, for pushing the maintenance of the unacknowledged messages can race with the close of the subscription because they are not maintained in the same synchronized block as deciding the client wants the message. BasicQueue::internalAddMessage() try { Subscription found = null; // In this synchronized block we decide that a client wants the message synchronized (receivers) { if (receivers.size() != 0) { for (Iterator it = receivers.iterator(); it.hasNext();) { Subscription sub = (Subscription) it.next(); if (sub.accepts(message.getHeaders())) { it.remove(); found = sub; break; } } } ... But only later outside this block do we maintain the unacknowledged messages // Queue to the receiver if (found != null) queueMessageForSending(found, message); This means that during the ... above a close of the subscription which leads to an invocation of hasUnackedMessages() could decide there are no unacknoweldged messages.