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From "Philip Harvey (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (QPID-3697) SortedQueue synchronization causes deadlock
Date Mon, 19 Dec 2011 14:33:30 GMT
SortedQueue synchronization causes deadlock
-------------------------------------------

                 Key: QPID-3697
                 URL: https://issues.apache.org/jira/browse/QPID-3697
             Project: Qpid
          Issue Type: Bug
          Components: Java Broker
    Affects Versions: 0.5, 0.15
         Environment: All
            Reporter: Philip Harvey


We've seen a broker become unresponsive several times in Production.

Analysis of a thread dump showed a deadlock between two threads, namely:

- a thread that is calling SortedQueue.enqueue, which has already locked the SortedQueue and
is trying to lock the Subscription's sendLock
- a thread that is closing a session by calling AMQChannel.unsubscribeAllConsumers, which
has already locked the Subscription's sendLock and is trying to lock the SortedQueue.

The suggested fix is for SortedQueue.enqueue to not be synchronized, thereby removing the
possibility of this deadlock occuring. SortedQueue.enqueue should instead lock on a private
Object.

Note that SortedQueue is the only queue that is susceptible to this deadlock because it is
the only one that has a synchronized enqueue method.


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