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https://issues.apache.org/jira/browse/SPARK-12049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15031864#comment-15031864
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Apache Spark commented on SPARK-12049:
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User 'srowen' has created a pull request for this issue:
https://github.com/apache/spark/pull/10042
> User JVM shutdown hook can cause deadlock at shutdown
> -----------------------------------------------------
>
> Key: SPARK-12049
> URL: https://issues.apache.org/jira/browse/SPARK-12049
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 1.5.2, 1.6.0
> Reporter: Sean Owen
> Assignee: Sean Owen
>
> Here's a simplification of a deadlock that can occur a shutdown if the user
> app has also installed a shutdown hook to clean up:
> - Spark Shutdown Hook thread runs
> - {{SparkShutdownHookManager.runAll()}} is invoked, locking
> {{SparkShutdownHookManager}} as it is {{synchronized}}
> - A user shutdown hook thread runs
> - User hook tries to call, for example {{StreamingContext.stop()}}, which is
> {{synchronized}} and locks it
> - User hook blocks when the {{StreamingContext}} tries to {{remove()}} the
> Spark Streaming shutdown task, since it's {{synchronized}} per above
> - Spark Shutdown Hook tries to execute the Spark Streaming shutdown task, but
> blocks on {{StreamingContext.stop()}}
> I think this is actually not that critical, since it requires a pretty
> specific setup, and I think it can be worked around in many cases by
> integrating with Hadoop's shutdown hook mechanism like Spark does so that
> these happen serially.
> I also think it's solvable in the code by not locking
> {{SparkShutdownHookManager}} in the 3 methods that are {{synchronized}} since
> these are really only protecting {{hooks}}. {{runAll()}} shouldn't hold the
> lock while executing hooks.
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