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From "Michael Pilone (JIRA)" <>
Subject [jira] [Commented] (CAMEL-5683) JMS connection leak with request/reply producer on temporary queues
Date Fri, 05 Oct 2012 14:12:03 GMT


Michael Pilone commented on CAMEL-5683:

Raul, I agree. I need to refresh my page before commenting :)

The more I think about it the trickier the problem gets. Using the ReferenceQueue on the SoftReferences
would help cleanup producers in the GC case, but you would need to make sure the cache also
handles the case where the LRU item is evicted when the capacity is reached. In the eviction
case, there is no ReferenceQueue to hold the item for later cleanup.

It might make sense to remove the SoftReference support and just keep the LRU/capacity behavior.
Then add a listener interface or "evicted queue" to the LRU hashmap to collect items (i.e.
producers) that have been evicted and are pending cleanup. It seems like the use of SoftReferences
undermines the LRU concept because the GC is deciding when to collect it rather than letting
the map track the last used time. In theory the GC is supposed to be bias against SoftRef
collection but it seems pretty aggressive from my simple tests. 

Something like java.util.LinkedHashMap gives you a removeEldestEntry method which would be
a nice place to hook in producer shutdown code and avoids these problems.
> JMS connection leak with request/reply producer on temporary queues
> -------------------------------------------------------------------
>                 Key: CAMEL-5683
>                 URL:
>             Project: Camel
>          Issue Type: Bug
>          Components: camel-jms
>    Affects Versions: 2.10.0
>         Environment: Apache Camel 2.10.0
> ActiveMQ 5.6.0
> Spring 3.2.1.RELEASE
> Java 1.6.0_27
> SunOS HOST 5.10 Generic_144488-09 sun4v sparc SUNW,SPARC-Enterprise-T5220
>            Reporter: Michael Pilone
>            Assignee: Claus Ibsen
>             Fix For: 2.9.4, 2.11.0, 2.10.2
>         Attachments:,,
Consumer List.txt, MAT Snapshot.png, Route Configuration.txt
> Over time I see the number of temporary queues in ActiveMQ slowly climb. Using JMX information
and memory dumps in MAT, I believe the cause is a connection leak in Apache Camel.
> My environment contains 2 ActiveMQ brokers in a network of brokers configuration. There
are about 15 separate applications which use Apache Camel to connect to the broker using the
ActiveMQ/JMS component. The various applications have different load profiles and route configurations.
> In the more active client applications, I found that ActiveMQ was listing 300+ consumers
when, based on my configuration, I would expect no more than 75. The vast majority of the
consumers are sitting on a temporary queue. Over time, the 300 number increments by one or
two over about a 4 hour period.
> I did a memory dump on one of the more active client applications and found about 275
DefaultMessageListenerContainers. Using MAT, I can see that some of the containers are referenced
by JmsProducers in the ProducerCache; however I can also see a large number of listener containers
that are no longer being referenced at all. I was also able to match up a soft-references
producer/listener endpoint with an unreferenced listener which means a second producer was
created at some point.
> Looking through the ProducerCache code, it looks like the LRU cache uses soft-references
to producers, in my case a JmsProducer. This seems problematic for two reasons:
> - If memory gets constrained and the GC cleans up a producer, it is never properly stopped.
> - If the cache gets full and the map removes the LRU producer, it is never properly stopped.
> What I believe is happening, is that my application is sending a few request/reply messages
to a JmsProducer. The producer creates a TemporaryReplyManager which creates a DefaultMessageListenerContainer.
At some point, the JmsProducer is claimed by the GC (either via the soft-reference or because
the cache is full) and the reply manager is never stopped. This causes the listener container
to continue to listen on the temporary queue, consuming local resources and more importantly,
consuming resources on the JMS broker.
> I haven't had a chance to write an application to reproduce this behavior, but I will
attach one of my route configurations and a screenshot of the MAT analysis looking at DefaultMessageListenerContainers.
If needed, I could provide the entire memory dump for analysis (although I rather not post
it publicly). The leak depends on memory usage or producer count in the client application
because the ProducerCache must have some churn. Like I said, in our production system we see
about 12 temporary queues abandoned per client per day.
> Unless I'm missing something, it looks like the producer cache would need to be much
smarter to support stopping a producer when the soft-reference is reclaimed or a member of
the cache is ejected from the LRU list.

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