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From "Amit Nithian (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1542) Deadlock in Configuration.writeXml when serialized form is larger than one DFS block
Date Sun, 26 Dec 2010 03:34:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1542?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12975088#action_12975088
] 

Amit Nithian commented on HDFS-1542:
------------------------------------

Hey guys,

Not sure where we are on this but it just hit me.. if I unapply the aforementioned patch that
added the synchronized keyword to the writeXML, then would the deadlock not happen? I don't
care about dumping the configuration at runtime for the moment but if I can get my jobs to
run then that would free up a lot of other internal tasks me and my team are doing. I suspect
I just need to do this and rebuild hadoop on the jobtracker machine which should minimize
any code changes across my cluster

Happy holidays!
Amit

> Deadlock in Configuration.writeXml when serialized form is larger than one DFS block
> ------------------------------------------------------------------------------------
>
>                 Key: HDFS-1542
>                 URL: https://issues.apache.org/jira/browse/HDFS-1542
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs client
>    Affects Versions: 0.22.0, 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>         Attachments: deadlock.txt, hdfs-1542.txt, Test.java
>
>
> Configuration.writeXml holds a lock on itself and then writes the XML to an output stream,
during which DFSOutputStream will try to get a lock on ackQueue/dataQueue. Meanwihle the DataStreamer
thread will call functions like conf.getInt() and deadlock against the other thread, since
it could be the same conf object.
> This causes a deterministic deadlock whenever the serialized form is larger than block
size.

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