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https://issues.apache.org/jira/browse/HADOOP-8325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13264396#comment-13264396
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Alejandro Abdelnur commented on HADOOP-8325:
--------------------------------------------

@Ravi, thread priority/group/context/privileges does not ensure 
order/serialization of execution given a number of processors/core greater than 
one (and I assume it is not guaranteed even in the case of a single core).
                
> 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, 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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