RE: Message lost due to NullpointerException in TopicConsumerEndpoint.deliverMessages

It appears to be a race condition. The stopDelivery() test prior to
removeFirstMessage() returns true if there are no messages available 
(getMessageCount() == 0). 
However, a single message that expires between the call to stopDelivery() 
and removeFirstMessage() means that removeFirstMessage() will return null
and trigger an NPE.
Its not clear that a message is lost however. The only way I can
see it happening is if a message expires, in which case it wouldn't be
delivered anyway.

> From: A. Schiefke (ancosys)
> 
> I have an application with 4 processes on 4 different 
> WinXP-PCs on a private network using tcp connectors. The 
> OpenJMS-Server (0.7.6.1) runs on one of these PCs. There are 
> less than 10 messages per second. I am using a single 
> connection, a single session and single publisher (per 
> process). All messages are non persistent. Memory and cpu 
> load of the pc hosting the jms-server is very moderate.
> 
> The App runs in a production environment for months and it 
> runs fine. No messages have got lost - until last friday. 
> Then we experienced a lost message. The jms log told me that 
> at the same time two NullPointerExceptions were thrown (see below).
> 
> I looked up the code of TopicConsumerEndpoint and found the following:
> 
> The second Exception (that is not caught regulary) seems to 
> be just a follow up error during the error treatment.
> 
> The first exception occurs because there is no MessageHandle 
> though the method is expecting one. But deliverMessage makes 
> no attempt to verify that removeFirstMessage return not null.
> 
> Can anybody give me a hint what was going wrong there? Maybe 
> there is synchronisation problem between the scheduling 
> thread and the executing thread concerning the message cache?
> 
> Of course i could make these messages persistent but I am not 
> shure whether this really would solve this special kind of 
> problem. Moreover there seem to be a strong performance 
> penalty for that.
> 
> Any help is appreciated.
> 
> 40   	2005-08-06	11:16:02	ERROR	[Scheduler-Worker-11] 
> messagemgr.TopicConsumerEndpoint	java.lang.NullPointerException
> java.lang.NullPointerException
> 	at
> org.exolab.jms.messagemgr.TopicConsumerEndpoint.deliverMessage
> s(TopicConsumerEndpoint.java:192)
> 	at
> org.exolab.jms.messagemgr.ConsumerEndpoint.run(ConsumerEndpoin
> t.java:425)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker.runIt(ThreadPoolWo
> rker.java:191)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker.runWork(ThreadPool
> Worker.java:178)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker.access$000(ThreadP
> oolWorker.java:67)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker$1.run(ThreadPoolWo
> rker.java:122)
> 	at java.lang.Thread.run(Thread.java:536)
> 
> 
> 260  	2005-08-06	11:16:02	ERROR	[Scheduler-Worker-11] 
> threadPool.ThreadPoolWorker	Thread Scheduler-Worker-11: uncaught 
> exception fell through from run()
> java.lang.NullPointerException
> 	at
> org.exolab.jms.messagemgr.ConsumerEndpoint.addMessage(Consumer
> Endpoint.java:670)
> 	at
> org.exolab.jms.messagemgr.ConsumerEndpoint.returnMessage(Consu
> merEndpoint.java:585)
> 	at
> org.exolab.jms.messagemgr.TopicConsumerEndpoint.deliverMessage
> s(TopicConsumerEndpoint.java:211)
> 	at
> org.exolab.jms.messagemgr.ConsumerEndpoint.run(ConsumerEndpoin
> t.java:425)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker.runIt(ThreadPoolWo
> rker.java:191)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker.runWork(ThreadPool
> Worker.java:178)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker.access$000(ThreadP
> oolWorker.java:67)
> 	at
> org.exolab.core.threadPool.ThreadPoolWorker$1.run(ThreadPoolWo
> rker.java:122)
> 	at java.lang.Thread.run(Thread.java:536)
> -- 
> 
> Mit freundlichen Grüssen,
> 
> Andreas Schiefke
> Dr. rer. nat.
> 
> ancosys gmbh
> Büro Rhein-Ruhr
> Gerhard-Hebborn-Str. 31
> 42699 Solingen
> 
> Tel: 0212/38 24 661
> Fax: 0212/38 24 662
> email: [email protected]
> 
> 
> 
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SF.Net email is Sponsored by the Better Software Conference & EXPO
September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf