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https://issues.apache.org/activemq/browse/AMQ-1251?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_40016
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David Sitsky commented on AMQ-1251:
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Hi Vadim,
I can't use the receive call, since my application uses the async
MessageListener interface. I posted on the activemq-user mailing list more
detail on my application, with a unit test which demonstrates the issue.
http://www.nabble.com/Large-PendingQueueSize-values-for-subscriptions-on-a-queue-with-one-message-tf4316080s2354.html.
I've attached a unit test which demonstrates the problem. I tried to make the
code as small as possible.
In this situation, the issue (program hangs) seems to happen when
QUEUE_PREFETCH_SIZE == 1 and NUM_WORKERS = 2 (90% of the time).
Changing NUM_WORKERS to 1 seems to make it work.
Increasing the QUEUE_PREFETCH_SIZE also seems to make things work.
> Broker stops delivering messages to some consumers
> --------------------------------------------------
>
> Key: AMQ-1251
> URL: https://issues.apache.org/activemq/browse/AMQ-1251
> Project: ActiveMQ
> Issue Type: Bug
> Components: Broker
> Affects Versions: 4.1.0
> Environment: WinXP
> Reporter: Vadim Pesochinskiy
> Assignee: Rob Davies
> Fix For: 5.0.0
>
>
> I have around 40 consumers taking messages from a single queue. After awhile
> 1 or 2 consumers stop receiveing any messages. Going to JMX and stopping
> corresponding connection causes re-connect and messages are delivered again.
> I reproduced it twice in QA enviroment and now it happened in production. I
> tried to instrument the code and set the log in debug, but that changed
> timing and I failed to reproduce it after the changes.
> I suspect that runtime association b/w Queue and Consumer objects is lost on
> the Broker side.
> One of the suspects is the empty catch block in the RoundRobinDispatchPolicy
> (line 64) class. It is possible that the CopyOnWrite array list is messed up
> and it fails when removed consumer is added back.
> BTW CopyOnWrite list is good when you mostly read, but not so good when you
> write for every message delivery and empty catch blocks are bad in any case.
> if (firstMatchingConsumer != null) {
> // Rotate the consumer list.
> try {
> consumers.remove(firstMatchingConsumer);
> consumers.add(firstMatchingConsumer);
> } catch (Throwable bestEffort) {
> }
> }
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