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From "Ravi Prakash (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8325) Add a ShutdownHookManager to be used by different components instead of the JVM shutdownhook
Date Sat, 28 Apr 2012 16:28:48 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13264354#comment-13264354
] 

Ravi Prakash commented on HADOOP-8325:
--------------------------------------

Hey Tucu! What functionality does this Shutdown Hook Manager provide that the JVM shutdown
hook manager does not? http://docs.oracle.com/javase/1.4.2/docs/guide/lang/hook-design.html
states
bq. The thread can be created in the proper thread group, given the correct priority, context,
and privileges, and so forth. 
We can set priorities of the existing shutdown thread and since the JVM uses a preemptive,
priority based scheduling algorithm, they will in essence run in order of priorities (two
threads may have the same priorities but that is besides the point).
                
> 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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