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From "Matt Banner (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FELIX-3055) Event Admin deadlocks when sendEvent is called from within a handleEvent method
Date Tue, 26 Jul 2011 18:17:09 GMT
Event Admin deadlocks when sendEvent is called from within a handleEvent method
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                 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
            Reporter: Matt Banner


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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