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From "Peter Voss (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1542) Deadlock in Configuration.writeXml when serialized form is larger than one DFS block
Date Thu, 23 Dec 2010 15:07:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1542?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12974636#action_12974636
] 

Peter Voss commented on HDFS-1542:
----------------------------------

Hi Todd,

I might be the wrong person to judge, but I totally agree with you that avoiding synchronization
and locking in the first place is a very good idea. Therefore it seems totally valid to make
a copy of the Configuration. I don't like the "feature" that changing settings in the configuration
after the FS was created is reflected in open streams. I think this adds unnecessary complexity
and synchronization issues. I like your solution.

> 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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