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https://issues.apache.org/jira/browse/AMQ-3506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109338#comment-13109338
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Torsten Mielke commented on AMQ-3506:
-------------------------------------
Claudio's suggestion should also work (using newPool.close() to discard the
pool). I tested it against the JUnit tests of activemq-pool and against a Camel
route that consumes from JMS.
It has the advantage that once the cache contains a pool object, there is no
additional overhead. All overhead is only in the case when the cache does not
yet contain the key.
In my solution there is a synchronized call for every createSession()
invocation.
> Access to ConnectionPool.createSession needs to be synchronized
> ----------------------------------------------------------------
>
> Key: AMQ-3506
> URL: https://issues.apache.org/jira/browse/AMQ-3506
> Project: ActiveMQ
> Issue Type: Bug
> Components: Broker
> Affects Versions: 5.5.0
> Environment: activemq-pool, PooledConnectionFactory with
> maximumActive=1 and blockIfSessionPoolIsFull=true (default behavior)
> Reporter: Torsten Mielke
> Labels: activemq-pool, maximumActive, sessionPool
> Fix For: 5.6.0
>
> Attachments: AMQ-3506.patch
>
> Original Estimate: 3h
> Remaining Estimate: 3h
>
> When configuring a PooledConnectionFactory with maximumActive=1 and
> blockIfSessionPoolIsFull=true (default behavior for latter config) it is
> possible that multiple threads that concurrently try to use the same JMS
> connection to create a new session might create more sessions than the
> configured maximumActive limit.
> That's because the call to ConnectionPool.createSession() is not synchronized
> and if multiple threads try to call this method concurrently (on the same
> underlying JMS connection) then the if-condition in
> {code:java}
> SessionKey key = new SessionKey(transacted, ackMode);
> SessionPool pool = cache.get(key);
> if (pool == null) {
> pool = createSessionPool(key);
> cache.put(key, pool);
> }
> {code}
> will evaluate to true for *all* threads and they all end up creating their
> own sessionPool using the same SessionKey properties.
> Access to the if-condition needs to be synchronized so that only one session
> pool gets created. That will ensure that not more than the configured
> maximumActive number of sessions can get created.
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