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From "Torsten Mielke (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMQ-3506) Access to ConnectionPool.createSession needs to be synchronized
Date Wed, 21 Sep 2011 08:31:09 GMT

    [ https://issues.apache.org/jira/browse/AMQ-3506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109338#comment-13109338
] 

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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