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https://issues.apache.org/jira/browse/IMAP-372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13633893#comment-13633893
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Andrzej Rusin commented on IMAP-372:
------------------------------------

Eric,

It's the jstack tool from standard Sun/Oracle JDK. It identifies and shows the 
deadlock (probably depending on command line arguments) when it exists.

I believe it can be done manually too, by looking at what threads obtained any 
locks and what threads are waiting for them. If there is a loop in the graph 
constructed from these dependencies, then there is a deadlock.
                
> Deadlock in AbstractDelegatingMailboxListener under load
> --------------------------------------------------------
>
>                 Key: IMAP-372
>                 URL: https://issues.apache.org/jira/browse/IMAP-372
>             Project: James Imap
>          Issue Type: Bug
>          Components: Mailbox
>            Reporter: Andrzej Rusin
>            Assignee: Eric Charles
>         Attachments: James Listener Deadlock.txt
>
>
> In AbstractDelegatingMailboxListener::event, firing the events inside the 
> synchronized blocks causes a deadlock involving:
> lock on HashMapDelegatingMailboxListener::listeners
> (synchronized methods) lock on SelectedMailboxImpl
> In my example, these 3 methods got interlocked:
> AbstractDelegatingMailboxListener.addListener
> SelectedMailboxImpl.msn
> AbstractDelegatingMailboxListener.removeListener
> My idea to fix it is basically to take the for loop on mListeners outside the 
> synchronized block in 
> org.apache.james.mailbox.store.AbstractDelegatingMailboxListener.event(Event).
>  That will not make the propagated event processing in SelectedMailboxImpl 
> hit the synchronized lock on listeners.

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