[jira] [Commented] (AMQ-6626) Deadlock caused by ActiveMQMessageConsumer.dispatch() due to onEvent invocation

["Timothy Bish (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AMQ-6626?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15924163#comment-15924163 ] 

Timothy Bish commented on AMQ-6626:
-----------------------------------

If you can create a test case that excludes the external dependencies and shows an actual problem with the *ActiveMQ* code we can take a look, otherwise I'd suggest contacting the third parties where the problem appears to be.  

> Deadlock caused by ActiveMQMessageConsumer.dispatch() due to onEvent invocation
> -------------------------------------------------------------------------------
>
>                 Key: AMQ-6626
>                 URL: https://issues.apache.org/jira/browse/AMQ-6626
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: JMS client
>            Reporter: Facundo Velazquez
>
> Hi. 
> In Mule ESB, 
> I have detected a deadlock caused by the interaction between Spring and ActiveMQ.
> Basically, there are two execution chains that are causing the deadlock:
> First Chain: when a Message arrives to the JMS Queue:
> 1) ActiveMQMessageConsumer.dispatch() gets the lock of FifoMessageDispatchChannel.mutex.
> 2) ActiveMQMessageConsumer.dispatch() calls the onMessage() method without releasing the lock.
> 3) onMessage Mule Implementation calls org.springframework.SingleConnectionFactory$SharedConnectionInvocationHandler.invoke() because It needs a toString of the used resource (in this case the connection) to logging purposes.
> 3) in ToString() method, org.springframework.SingleConnectionFactory.getConnection() method is called and It takes the org.springframework.SingleConnectionFactory.connectionMonitor lock to access to connection (that's a shared resource).
> Lock ordering in this chain:
> FifoMessageDispatchChannel.mutex lock -> org.springframework.SingleConnectionFactory.connectionMonitor lock
> Second Chain: when A reconnection-strategy is applied:
> 1) Mule stops the current connection calling org.springframework.SingleConnectionFactory.localStop()
> 2) LocalStop takes the org.springframework.SingleConnectionFactory.connectionMonitor lock.
> 3) After a chain of calls: FifoMessageDispatchChannel.stop() is called.
> 4) FifoMessageDispatchChannel.stop() takes the FifoMessageDispatchChannel.mutex lock.
> Lock Ordering in this case: 
> org.springframework.SingleConnectionFactory.connectionMonitor lock -> FifoMessageDispatchChannel.mutex lock 
> As you can see, The chains don't take care about lock ordering, and It's causing a deadlock.
> I've sent a mail with same subject to the user list.
> Although I agree the best and faster solution is to not use the string() method of the connection in log (because It's taking a lock), and I'll remove it in Mule code, I think would be desirable to not call onEvent method without realising the adquired lock, to avoid potential deadlocks. 
> Thanks.



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