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From "Sergiy Barlabanov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMQ-4166) RedeliveryPlugin causes a deadlock with JobSchedulerImpl
Date Tue, 13 Nov 2012 14:52:13 GMT

    [ https://issues.apache.org/jira/browse/AMQ-4166?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13496233#comment-13496233
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Sergiy Barlabanov commented on AMQ-4166:
----------------------------------------

I will try 5.8-SNAPSHOT the next days and write the feedback.
                
> RedeliveryPlugin causes a deadlock with JobSchedulerImpl
> --------------------------------------------------------
>
>                 Key: AMQ-4166
>                 URL: https://issues.apache.org/jira/browse/AMQ-4166
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.7.0
>         Environment: Reproduced on Windows 8, Windows Vista, MacOS X
> with Oracle jdk 1.7.0_07. ActiveMQ is started embedded using RAR inside Glassfish 3.1.2.2.
>            Reporter: Sergiy Barlabanov
>         Attachments: broker-config.xml, stack-trace-1.txt, stack-trace-2.txt
>
>
> Originates from the forum discussion http://activemq.2283324.n4.nabble.com/RedeliveryPlugin-causes-a-deadlock-with-JobSchedulerImpl-in-ActiveMQ-5-7-0-tt4659019.html
> we have RedeliveryPlugin causing thread deadlock together with JobSchedulerImpl. ActiveMQ
version is 5.7.0. We activated RedeliveryPlugin in our broker config xml (see below). There
two stacktraces below as well. One is from ActiveMQ VMTransport thread, which tries to send
a message to a dead letter queue using RedeliveryPlugin. RedeliveryPlugin just tries to reschedule
the message for redelivery and for that it calls JobSchedulerImpl and blocks on its synchronized
method "schedule". On the way "consumersLock" is locked. 
> Another stack trace is from JobScheduler:JMS thread, which fires a job to redeliver some
message and tries to send it using the same queue used by the VMTransport thread. And it blocks
on that consumersLock locked by the VMTransport thread. And this occurs in JobSchedulerImpl#mainLoop
method inside synchronized {} block causing a deadlock, since the VMTransport thread tries
to call another synchronized method of JobSchedulerImpl. The art how RedeliveryPlugin and
JobSchedulerImpl are programmed seems to be quite dangerous, since they both access the queues
and try to acquire queue locks. And additionally synchronized methods of JobSchedulerImpl
are called directly from RedeliveryPlugin making that to a nice source of thread deadlocks.
And I see no measures taken in the code to avoid these deadlocks.
> We can reproduce it quite often if we start ActiveMQ with empty stores (kahadb and scheduler
stores are deleted manually from the file system before startup). But looking at the code,
I would say that the problem may occur in any situation in any deployment scenario (standalone
or embedded in a JEE container). It is just enough to have some Transport thread redelivering
a message and the JobScheduler thread trying to fire a job at the same moment on the same
queue.
> And another strange thing, which is may be has nothing to do with the deadlock but is
still strange, is that according to the stack trace RedeliveryPlugin tries to redeliver an
expired message.
> broker config and the stack traces are attached to the issue.

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