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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4521) A JobInProgressLIstener can change a job without informing other listeners
Date Sat, 25 Oct 2008 13:17:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642619#action_12642619

Amar Kamat commented on HADOOP-4521:

One way I can think is to have  the listeners add themselves to a {{JobListenerManager}} which
will be implemented by the {{JobTracker}}. The {{JobListenerManager}} interface, for now,
will implement the following interfaces 
- addJobInProgressListener(JobInProgressListener)
- removeJobInProgressListener(JobInProgressListener)
- update(JobChangeEvent)

For example a listener might init the job, generate an event and then inform the {{JobListenerManager}}
about it.

Also the {{JobInProgressListener}} interface should add itself to the {{JobListenerManager}}
rather than some third party adding it. This can be done by adding a {{addJobListenerManager(JobListenerManager)}}
interface to {{JobInProgressListener}} or extend the listener's constructor to accept a {{JobListenerManager}}.

Internally the listener should maintain the reference to the {{JobListenerManager}} and should
change/update a job only via {{JobListenerManager.update()}}. 
JobListenerManager should take the responsibility of updating other listeners.

> A JobInProgressLIstener can change a job without informing other listeners
> --------------------------------------------------------------------------
>                 Key: HADOOP-4521
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4521
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Amar Kamat
> As of now the {{JobInProgressListener}} adds itself to the {{JobTracker}} and gets updated/informed.
Some of there {{JobInProgressListener}}'s control these changes/events (e.g.  {{EagerTaskInitializer}}).
The issue with this model is that a listener can change the job without informing other listeners.

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