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https://issues.apache.org/jira/browse/CAMEL-5683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13470346#comment-13470346
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Michael Pilone commented on CAMEL-5683:
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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: https://issues.apache.org/jira/browse/CAMEL-5683
> 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: CamelConnectionLeak-ProducerTemplate.zip,
> CamelConnectionLeak.zip, 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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