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https://issues.apache.org/jira/browse/MAPREDUCE-5384?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Karthik Kambatla updated MAPREDUCE-5384:
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    Attachment: mr-5384-1.patch

Uploading a patch that refactors {{DelegationTokenRenewal}} to address the 
races and improves readability.

Following are the major changes:
# {{RenewalTimerTask}} along with scheduling/cancelling logic is moved to 
{{DelegationTokenToRenew}}
# {{DelegationTokenToRenew#timerTask}} is used to capture the cancellation of 
both token/{{TimerTask}}.
                
> Race in DelegationTokenRenewal#RenewalTimerTask
> -----------------------------------------------
>
>                 Key: MAPREDUCE-5384
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5384
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 1.2.1
>            Reporter: Karthik Kambatla
>            Assignee: Karthik Kambatla
>         Attachments: mr-5384-0.patch, mr-5384-1.patch
>
>
> There are a couple of races in DelegationTokenRenewal. 
> One of them was addressed by MAPREDUCE-4860, which introduced a deadlock 
> while fixing this race. Opening a new JIRA per discussion in MAPREDUCE-5364, 
> since MAPREDUCE-4860 is already shipped in a release.
> Races to fix:
> # TimerTask#cancel() disallows future invocations of run(), but doesn't abort 
> an already scheduled/started run().
> # In the context of DelegationTokenRenewal, RenewalTimerTask#cancel() only 
> cancels that TimerTask instance. However, it has no effect on any other 
> TimerTasks created for that token. 

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