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https://issues.apache.org/jira/browse/AMQ-3506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13108855#comment-13108855
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Claudio Corsi edited comment on AMQ-3506 at 9/20/11 5:49 PM:
-------------------------------------------------------------
We might consider redefining the cache field from Map to ConcurrentMap and
change the code somewhat.
{code:java}
public Session createSession(boolean transacted, int ackMode) throws
JMSException {
SessionKey key = new SessionKey(transacted, ackMode);
SessionPool pool = null;
pool = cache.get(key);
if (pool == null) {
SessionPool newPool = createSessionPool(key);
SessionPool prevPool = cache.putIfAbsent(key, newPool);
if (prevPool != null && prevPool != newPool) {
// newPool was not the first one to be associated with this
key... close created session pool
newPool.destroy(); // don't remember the method call
}
pool = cache.get(key); // this will return a non-null value...
}
PooledSession session = pool.borrowSession();
return session;
}
{code}
was (Author: ccorsi):
We might consider redefining the cache field from Map to ConcurrentMap and
change the code somewhat.
<code:java>
public Session createSession(boolean transacted, int ackMode) throws
JMSException {
SessionKey key = new SessionKey(transacted, ackMode);
SessionPool pool = null;
pool = cache.get(key);
if (pool == null) {
SessionPool newPool = createSessionPool(key);
SessionPool prevPool = cache.putIfAbsent(key, newPool);
if (prevPool != null && prevPool != newPool) {
// newPool was not the first one to be associated with this
key... close created session pool
newPool.destroy(); // don't remember the method call
}
pool = cache.get(key); // this will return a non-null value...
}
PooledSession session = pool.borrowSession();
return session;
}
</code>
> 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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