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From "David Sitsky (JIRA)" <j...@apache.org>
Subject [jira] Updated: (AMQ-1251) Broker stops delivering messages to some consumers
Date Wed, 05 Sep 2007 02:00:24 GMT

     [ https://issues.apache.org/activemq/browse/AMQ-1251?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

David Sitsky updated AMQ-1251:
------------------------------

    Attachment: TestActiveMQSyncReceive.java

Similar unit test to TestActiveMQ, except it has been rewritten to use synchronous receives,
which is how my main application works now.

I still get the unit test hanging about 50% of the time when the number of worker threads
is 2 or more, and interestingly when the prefetch size is 0.  If the prefetch is set to 1
or more, then the program _seems_ to work.

Whatever the problem is, both with this test and the previous one, there is some sort of race
condition, since the program doesn't always hang.

Whenever the program hangs, it seems the PendingQueueSize values for the queue subscriptions
are very large, in fact when I add the values up from all worker queue subscriptions, it seems
to equal the total number of messages which have been sent to the queue.

When the program works, as expected, the PendingQueueSize on the subscriptions is 0.

Any ideas what is wrong?  This is with checkout 572492 and built using mvn -Dmaven.test.skip=true
clean install.



> 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
>
>         Attachments: TestActiveMQ.java, TestActiveMQSyncReceive.java
>
>
> 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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