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https://issues.apache.org/jira/browse/HADOOP-3415?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598933#action_12598933
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Alejandro Abdelnur commented on HADOOP-3415:
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I'm fine with such changes, as you claim the current implementation could have
issues in a testing environment.
Regarding #3, the queue should be initialized then on startNotifier() to ensure
it's clean.
> JobEndNotifier isnt synchronized, doesnt check state before acting
> ------------------------------------------------------------------
>
> Key: HADOOP-3415
> URL: https://issues.apache.org/jira/browse/HADOOP-3415
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.16.3
> Reporter: Steve Loughran
> Priority: Minor
>
> JobEndNotifier is pretty hazardous inside.
> 1. the static startNotifier isnt synchronized, and doesnt check for being
> already running before it creates a new worker thread. It should be
> sycnhronized and a no-op if there is a live thread.
> 2. stopNotifier() should be a no-op if already stopped. It MUST NOT call
> thread.interrupt() in such a state, as thread may be null.
> 3. the registerNotification method also assumes that the static queue is non
> null.
> Things would be a lot safer by making this class part of a JobTracker, not a
> singleton with static methods, as then you could more safely make assumptions
> about object state. This would not only eliminate a lot of reentrancy
> problems, but tie the life of the notifier to that of its owner, the
> JobTracker.
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