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Date: Mon, 12 Nov 2007 01:50:22 -0800 (PST)
From: "Rainer Klute (JIRA)" <jira@apache.org>
To: dev@activemq.apache.org
Subject: [jira] Created: (AMQ-1490) Deadlocks (with JUnit tests)
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Deadlocks (with JUnit tests)
----------------------------

                 Key: AMQ-1490
                 URL: https://issues.apache.org/activemq/browse/AMQ-1490
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 5.0.0
         Environment: Linux
            Reporter: Rainer Klute
             Fix For: 5.0.0


For some time now there have been various bug reports about ActiveMQ "blocking", "not receiving messages", "running into a deadlock" etc. Since I encoutered such deadlocks now and then, too, I eventually wrote up a JUnit testing scenario for this stuff. I found out that deadlocks can be quite easily reproduced. The symptoms are that the producer thread is sending or committing while the consumer thread is receiving or committing - and none of them can advance. One of the threads is always stuck in a blocking queue.

Here's a sample output of my testing class:
 An ActiveMQ deadlock has been discovered. The following threads seem to be involved:

 Thread "producer" is inactive since 16 seconds after 358719 status changes. The current status is COMMITTING
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
  java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1889)
 java.util.concurrent.ArrayBlockingQueue.take(ArrayBlockingQueue.java:317)
 org.apache.activemq.transport.FutureResponse.getResult(FutureResponse.java:40)
 org.apache.activemq.transport.ResponseCorrelator.request(ResponseCorrelator.java:76)
 org.apache.activemq.ActiveMQConnection.syncSendPacket(ActiveMQConnection.java:1172)
 org.apache.activemq.TransactionContext.commit(TransactionContext.java:259)
 org.apache.activemq.ActiveMQSession.commit(ActiveMQSession.java:494)
 de.rainer_klute.activemq.ProducerThread.run(ProducerThread.java:162)

 Thread "consumer" is inactive since 16 seconds after 1807 status changes. The current status is RECEIVING
 java.lang.Object.wait(Native Method)
 java.lang.Object.wait(Object.java:485)
 org.apache.activemq.MessageDispatchChannel.dequeue(MessageDispatchChannel.java:75)
 org.apache.activemq.ActiveMQMessageConsumer.dequeue(ActiveMQMessageConsumer.java:404)
 org.apache.activemq.ActiveMQMessageConsumer.receive(ActiveMQMessageConsumer.java:452)
 org.apache.activemq.ActiveMQMessageConsumer.receive(ActiveMQMessageConsumer.java:504)
 de.rainer_klute.activemq.ConsumerThread.run(ConsumerThread.java:183)

The following factors seem to increase the probability of a deadlock:
* small values for memoryUsage
* working transacted in the consumer (not always necessary but "helps")
* many messages in the persistence store (to be achieved via a long delay before the consumer starts to read messages)


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