Need to manipulate the thread order to exercise the race condition so I needed to use a DEBUGGER. 1) Set a (* thread only *) breakpoint at line number 268 - "onConnectionOpen();" if (protonConnection.getLocalState() == EndpointState.UNINITIALIZED && protonConnection.getRemoteState() != EndpointState.UNINITIALIZED) { onConnectionOpen(); } 2) Run the attached unit test in DEBUG mode. The unit test creates a subscriber. 3)The unit test triggers the breakpoint (from point 1). After a few seconds it tears down the connection between client and broker. In the console output is 15-05-10 11:05:20,510 | INFO | Thread -2 | About to close PROXY... 2015-05-10 11:05:20,510 | INFO | Thread -2 | close, numConnections=1 2015-05-10 11:05:20,511 | INFO | Thread -2 | PROXY closed. 4) Release the breakpoint. 5) The test remains running for 5 minutes. You can see the CPU usage for the process rise and see error message similar to following logged ~~~~ 2015-05-10 11:05:58,974 | WARN | ActiveMQ Transport: tcp:///127.0.0.1:54122@54114 | Transport Connection to: tcp://127.0.0.1:54122 failed: java.net.SocketException: Broken pipe Exception in thread "Activ Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "ActiveMQ Transport Server: amqp+nio+ssl://0.0.0.0:0" eMQ Transport Server: amqp+ssl://0.0.0.0:0" Exception in thread "ActiveMQ Transport Server Thread Handler: amqp+nio+ssl://0.0.0.0:0" Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "ActiveMQ Transport Server Thread Handler: amqp+ssl://0.0.0.0:0" Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "ActiveMQ Transport Server: amqp://0.0.0.0:0" Exception in thread "Reference Handler" Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "ActiveMQ Transport Server: amqp+ssl://0.0.0.0:0" java.lang.OutOfMemoryError: GC overhead limit exceeded Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "Reference Handler" org.apache.activemq.transport.amqp.AmqpProtocolException: Could not process AMQP commands Exception in thread "ActiveMQ Transport Server Thread Handler: amqp+nio://0.0.0.0:0" java.lang.OutOfMemoryError: GC overhead limit exceeded Exception in thread "ActiveMQ Transport Server: amqp+nio://0.0.0.0:0" java.lang.OutOfMemoryError: Java heap space ~~~~