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https://issues.apache.org/jira/browse/HADOOP-8325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13264033#comment-13264033
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Alejandro Abdelnur commented on HADOOP-8325:
--------------------------------------------
Thanks Nicholas,
#1, will do
#2, i thought about this, but it seemed counter intuitive to reverse the
comparison. As this is done only once and the number of hooks would always be
small, I don't see it as an issue. Because of that I'd prefer to keep it like
it is.
#3, that woud require the iterator() method to be public giving access to
anybody to the shutdown hooks and potentially invoking them outside of the
ShutdownHookManager. The getShutdownHooksInOrder() method is package private
only for test purposes (otherwise it would be private). Regarding the copying,
same rationale as in #2.
> Add a ShutdownHookManager to be used by different components instead of the
> JVM shutdownhook
> --------------------------------------------------------------------------------------------
>
> Key: HADOOP-8325
> URL: https://issues.apache.org/jira/browse/HADOOP-8325
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs
> Affects Versions: 2.0.0
> Reporter: Alejandro Abdelnur
> Assignee: Alejandro Abdelnur
> Priority: Critical
> Fix For: 2.0.0
>
> Attachments: HADOOP-8325.patch, HADOOP-8325.patch, HADOOP-8325.patch,
> HADOOP-8325.patch
>
>
> FileSystem adds a JVM shutdown hook when a filesystem instance is cached.
> MRAppMaster also uses a JVM shutdown hook, among other things, the
> MRAppMaster JVM shutdown hook is used to ensure state are written to HDFS.
> This creates a race condition because each JVM shutdown hook is a separate
> thread and if there are multiple JVM shutdown hooks there is not assurance of
> order of execution, they could even run in parallel.
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