Sean Owen created SPARK-12049:
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Summary: 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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