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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8684) Deadlock between WritableComparator and WritableComparable
Date Thu, 30 Aug 2012 01:15:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8684?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13444591#comment-13444591
] 

Hiroshi Ikeda commented on HADOOP-8684:
---------------------------------------

I think the reentrant lock is not needed.
In each of the sections guraded by the reentrant lock, the concurrent map is accessed only
once.

Incidentally, I think it is better to make the concurrent map to be final.
                
> Deadlock between WritableComparator and WritableComparable
> ----------------------------------------------------------
>
>                 Key: HADOOP-8684
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8684
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 1.0.3, 3.0.0
>            Reporter: Hiroshi Ikeda
>            Assignee: Jing Zhao
>            Priority: Minor
>         Attachments: Hadoop-8684.patch, Hadoop-8684.patch, Hadoop-8684.patch, WritableComparatorDeadLockTestApp.java
>
>
> Classes implementing WriableComparable in Hadoop call the method WritableComparator.define()
in their static initializers. This means, the classes call the method define() while thier
class loading, under locking their class objects. And, the method WritableComparator.define()
locks the WritableComaprator class object.
> On the other hand, WritableComparator.get() also locks the WritableComparator class object,
and the method may create instances of the targeted comparable class, involving loading the
targeted comparable class if any. This means, the method might try to lock the targeted comparable
class object under locking the WritableComparator class object.
> There are reversed orders of locking objects, and you might fall in deadlock.

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