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https://issues.apache.org/jira/browse/HADOOP-3628?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12611549#action_12611549
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Steve Loughran commented on HADOOP-3628:
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Looking at TaskTracker, can also gain this lifecycle. The big complication is
it has an inner bit that is started/stopped with initialize()/close(), within a
bigger lifecycle that manages the web service; this is only terminated with
shutdown().
So TaskTracker would need adapting as follows
-the start() operation starts everything up
-the terminate() operation is mapped to TaskTracker.shutdown()
-ping checks for the presence of the web server only.
-initialize() and close() do not change service state, they just reset a
running service.
-if you try and initialize() a service that is not yet started, it is started.
This is a bit fiddly, but would keep the basic idea: you can close() and
initialize() to reset most but not all of the service.
> 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,
> 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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