[jira] [Resolved] (FELIX-3055) Event Admin deadlocks when sendEvent is called from within a handleEvent method

["Carsten Ziegeler (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FELIX-3055?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Carsten Ziegeler resolved FELIX-3055.
-------------------------------------

       Resolution: Fixed
    Fix Version/s: eventadmin-1.2.14

Many thanks for reporting this, Matt!

Actually we had two problems: one of the this deadlock, but after fixing this I ran into starvation problems if more threads than the pool offers send cascading events. While the whole pool is processing the "outer" events, inner event sending is blocked as the pool has no free thread.

I've fixed both in revision 1151755 and ran some new tests on this version including
the tck. I couldn't detect any problems.

Would be great, Matt, if you could run your tests as well to verify.

Thanks!

> Event Admin deadlocks when sendEvent is called from within a handleEvent method
> -------------------------------------------------------------------------------
>
>                 Key: FELIX-3055
>                 URL: https://issues.apache.org/jira/browse/FELIX-3055
>             Project: Felix
>          Issue Type: Bug
>          Components: Event Admin
>    Affects Versions: eventadmin-1.2.12
>         Environment: Win2K8 R2, Java 1.6.0_17
>            Reporter: Matt Banner
>            Assignee: Carsten Ziegeler
>             Fix For: eventadmin-1.2.14
>
>         Attachments: TestClass.java, threaddump.txt
>
>
> The Felix Event Admin service doesn't correctly handle the case where EventAdmin.sendEvent(Event) is called from within an EventHandler.handleEvent(Event) implementation.  This happens whether the original event (the one being handled by the EventHandler, not the one it is dispatching) was dispatched using EventAdmin.sendEvent(Event) or EventAdmin.postEvent(Event).
> I have attached some sample code which should make this easy to reproduce.  Every time you invoke the "dispatch foo" command from the GoGo shell, it will post a "foo" event.  The handler for this event then attempts to send a new "bar" event.  Every time this happens, a thread in the event admin pool will become deadlocked.  If you run the dispatch command more times than the minimum number of threads in the pool (I think 20, by default), they will all be deadlocked and the event admin service will stop invoking event handlers (it seemed strange to me that this happens when you hit the minimum number of thread in the pool rather than the maximum, but I haven't had time to investigate that).
> Also attached is a thread dump from when all 20 threads have become deadlocked.  Note that they are all stuck on line 240 of SyncDeliverTasks.java waiting on a rendezvous with the timer barrier (line numbers refer to the current revision on trunk, r1074155).  I suspect that this is because the attempt to rendezvous on line 266 is met by the attempt on line 208 in the case where the event handler recursively calls sendEvent, leaving line 240 with no corresponding call to meet.

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