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From "James Strachan" <>
Subject Re: ConcurrentModificationException
Date Mon, 03 Apr 2006 18:54:39 GMT
Hi Kevin

On 4/3/06, Kevin Kessler <> wrote:
> I'm checking out ActiveMQ embedded in JBoss by firing as many messages as I
> can on a Topic to an MDB that just counts and logs the messages.  After
> sending a few thousand messages, the server would blow up with a
> ConcurrentModificationException because of a LinkedList in the
> class, in the
> dispatchMatched() method.  This would totally hose the server so bad I would
> have to kill -9 JBoss to get it to shutdown.
> I put a synchronized(matched){} (matched is the name of the LinkList) around
> the entire loop that iterated through the LinkedList in the
> dispatchMatched() method, and the exception went away.  It's something you
> guys might want to look at.

Just out of interest - which version of the code were you using?  I've
just looked at the code in SVN HEAD and every access of the matched
LinkedList in TopicSubscription is wrapped in a synchronized block.

> BTW, I'm getting about 4000 messages per second now in my simple test; very
> impressive.

FWIW we've had way faster than that (I've seen a single thread do
20,000 message/second on dual opteron boxes); it could be the JBoss
part slowing us down :)



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