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Date: Mon, 7 Jul 2008 11:46:31 -0700 (PDT)
From: "Doug Cutting (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3628) Add a lifecycle interface for
 Hadoop components: namenodes, job clients, etc.
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    [ https://issues.apache.org/jira/browse/HADOOP-3628?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12611275#action_12611275 ] 

Doug Cutting commented on HADOOP-3628:
--------------------------------------

This is looking good to me.

> retrofits to NameNode, DataNode, JobTracker

Should we convert TaskTracker and SecondaryNameNode too?

> Add a lifecycle interface for Hadoop components: namenodes, job clients, etc.
> -----------------------------------------------------------------------------
>
>                 Key: HADOOP-3628
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3628
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs, mapred
>    Affects Versions: 0.19.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: AbstractHadoopComponent.java, hadoop-3628.patch
>
>
> I'd like to propose we have a standard interface for hadoop components, the things that get started or stopped when you bring up a namenode. currently, some of these classes have a stop() or shutdown() method, with no standard name/interface, but no way of seeing if they are live, checking their health of shutting them down reliably. Indeed, there is a tendency for the spawned threads to not want to die; to require the entire process to be killed to stop the workers. 
> Having a standard interface would make it easier for 
>  * management tools to manage the different things
>  * monitoring the state of things
>  * subclassing
> The latter is interesting as right now TaskTracker and JobTracker start up threads in their constructor; that's very dangerous as subclasses may have their methods called before they are full initialised. Adding this interface would be the right time to clean up the startup process so that subclassing is less risky.

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