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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 Mon, 30 Apr 2012 03:11:21 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13264664#comment-13264664
] 

Alejandro Abdelnur commented on HADOOP-8325:
--------------------------------------------

@Ravi,

the latest patch integrates Nicholas comments, reverse comparator and HashSet.

the 'fs.automatic.close' is per filesystem instance. It is not that we don't want to close
the filesystem, but we want to close it after we finished using it. The patch fixes the problem
mentioned in the description of the JIRA. Furthermore, there are other shutdown hooks in 
FileContext and in MR that may require the filesystems to be still open.
                
> 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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