fix for: https://issues.apache.org/jira/browse/AMQ-3319 Concurrent read / write to the list is not protected, instead a read lock around both access points is used. Switch to using a ConcurrentLinkQueue instead and remove the read lock around that code.
activemq/trunk/activemq-core/src/main/java/org/apache/activemq/broker/region/Queue.java