SortedQueue synchronization causes deadlock
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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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