Doug Jones created CURATOR-62:
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Summary: Leader Election Deadlock
Key: CURATOR-62
URL: https://issues.apache.org/jira/browse/CURATOR-62
Project: Apache Curator
Issue Type: Bug
Reporter: Doug Jones
Assignee: Jordan Zimmerman
I've noticed that it is possible for a leader election to deadlock if a thread
is interrupted while it is trying to acquire the mutex for the election.
I've created a forced example of this here:
https://github.com/dfjones/curator/commit/544220b1e6b51c2718a7d3511a74962ff1c5ff48
You can see deadlock by using my modified code and running the
LeaderSelectorExample. Some leaders may execute, but on my system I eventually
see deadlock. Note that I only see deadlock when running against a remote zk
server rather than the embedded test server. I'm using Zookeeper 3.4.5 on Mac
OS X 10.8.4.
>From what I can tell by inspecting the ZK state/watching in the debugger, the
>thread that is interrupted is able to successfully create the lock object in
>ZK. However, due to the interrupt an exception is generated and
>LockInternals#internalLockLoop never runs. Later, in LeaderSelector#doWork
>when mutex.release() is called this fails at the for lockData.
Once this occurs, the lock object in ZK is the oldest and will cause deadlock.
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