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From "Alessandro Monguzzi (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMQ-3760) Deadlock on Java Client when onMessage executes a synchronized method.
Date Thu, 08 Mar 2012 08:56:58 GMT

    [ https://issues.apache.org/jira/browse/AMQ-3760?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13225093#comment-13225093
] 

Alessandro Monguzzi commented on AMQ-3760:
------------------------------------------

In the unit test above I used a dedicated session for the producer. Only the consumers share
a session. 

So is it not possible to add a new Consumer to an already running session? Can't I change
the messageListener for a running consumer? 

If so, I think that the MessageConsumer.setMessageListener() should throw an Exception, not
stopping and restarting the session.
                
> Deadlock on Java Client when onMessage executes a synchronized method.
> ----------------------------------------------------------------------
>
>                 Key: AMQ-3760
>                 URL: https://issues.apache.org/jira/browse/AMQ-3760
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: JMS client
>    Affects Versions: 5.5.1
>         Environment: java version "1.6.0_30"
> Java(TM) SE Runtime Environment (build 1.6.0_30-b12)
> Java HotSpot(TM) Server VM (build 20.5-b03, mixed mode)
> OS: SunOs 10/06
>            Reporter: Alessandro Monguzzi
>              Labels: features
>         Attachments: ActiveMQDeadlock.zip
>
>
> Create a class with two synchronized methods synchMethod1 and synchMethod2. 
> syncMethod1 is invoked inside a messageListener object and only prints a message on stdout.
> syncMethod2 creates a new MessageConsumer with a new instance of MessageListener. All
the MessageConsumers created by synchMethod2 share the same session.
> All the consumers listen on the same Topic named "myDest".
> Create an infinite cycle that: 
> 1) send a message on Topic "myDest"
> 2) invoke syncMethod2
> 3) waits 10ms
> In attach the unit test source.
> As result, a deadlock is created between the "ActiveMQ Session Task" thread entering
in syncMethod1 having the ActiveMessageConsumer's mutex and my other thread executing the
syncMethod2 when the SimplePriorityMessageDispatchChannel.stop() method is invoked.
> This means that it's not possible to create or change MessageListeners on a running session,
even if the code seems to handle this case stopping and restarting the session.

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