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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8325) Add a ShutdownHookManager to be used by different components instead of the JVM shutdownhook
Date Fri, 27 Apr 2012 22:18:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13264033#comment-13264033
] 

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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