Threads Blocked On ActiveMQConnection.ensureConnectionInfoSent

Multiple threads get blocked trying to gain entrance to ActiveMQConnection.ensureConnectionInfoSent(). The one thread that gained access is blocking all other threads whilst waiting for a response from broker.

This issue is very similar to old one at https://issues.jboss.org/browse/PROD-1330 and seems related to https://issues.apache.org/jira/browse/AMQ-2798

The attached thread dump is also very similar to :

https://issues.jboss.org/secure/attachment/12377901/threaddump_03052012_632pm.log

Broker topology is a master-slave cluster.

In this case, the blockage does not occur when using a failover transport with just two broker URLs - only happens when a third broker URL is added or may just take longer when using a 2-broker URL. The blockage doesn’t occur right away, and seems to occur when master becomes quite busy. The thread holding the mutex seems to wait indefinitely.