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From "Marco Nicosia (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1461) Corner-case deadlock in TaskTracker
Date Mon, 18 Jun 2007 23:03:26 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1461?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Marco Nicosia updated HADOOP-1461:
----------------------------------

    Priority: Blocker  (was: Critical)

> Corner-case deadlock in TaskTracker
> -----------------------------------
>
>                 Key: HADOOP-1461
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1461
>             Project: Hadoop
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.12.3
>            Reporter: Arun C Murthy
>            Assignee: Arun C Murthy
>            Priority: Blocker
>             Fix For: 0.14.0
>
>         Attachments: HADOOP-1461_1_20070605.patch, main_taskcleanup_deadlock.txt
>
>
> Thanks to Koji for the attached stack-trace...
> Summary:
> main()
>   -> offerService()
>     -> markUnresponsiveTasks (locks the TaskTracker here)
>       -> purgeTask() 
>         -> removeTaskFromJob (waiting to lock the RunningJob object)
> taskCleanup
>   -> purgeJob (locks the RunningJob object)
>     -> TIP.jobHasFinished()
>       -> TIP.cleanup (waiting to lock the TaskTracker)
> -*-*-
> Clear-case of ordering issues during synchronization... it's a corner-case since it depends
on the child-vm getting unresponsive _and_ the cleanup thread kicking in; which is why I'm
marking this for 0.14.0 rather than 0.13.0 - what do others think about this?
> -*-*-
> Two possible solutions to break the deadlock cycle:
> a) Make TaskTracker.purgeJob a synchronized method, thus it locks the TaskTracker before
locking the RunningJob method.
> b) Make the TaskTracker.tasks map a *Collections.synchronizedMap*, thus doing away with
the need to lock the TaskTracker in TIP.cleanup
> I'd prefer a) since the TaskTracker.tasks is referenced in multiple places in synchronized
methods... and hence is a less intrusive change.
> -*-*- 
> Thoughts?

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