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https://issues.apache.org/jira/browse/HADOOP-6269?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12772425#action_12772425
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Hemanth Yamijala commented on HADOOP-6269:
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I looked at the patch using CopyOnWriteArrayList. It seems like a reasonable
approach to me, except for one point that I will mention in a bit. First I
would like to see what others think about the usage of CopyOnWriteArrayList.
The defaultResources structure is modified only once per resource in the
lifetime of an application - like a hadoop daemon or client. It is iterated
over more number of times - typically every time a configuration instance is
loaded in the application. Going from the javadoc for the CopyOnWriteArrayList,
it does seem the usage is appropriate. The result of using this structure is a
simpler code change that is fixing the problem at hand. Given these points,
does the patch seem like a right direction ? (Todd, your thoughts ?)
Now, regarding the patch, even if we do agree on using it, I suppose we might
still need to synchronize addDefaultResources, because the contains check needs
to be synchronized with the add check, no ?
> Missing synchronization for defaultResources in Configuration.addResource
> -------------------------------------------------------------------------
>
> Key: HADOOP-6269
> URL: https://issues.apache.org/jira/browse/HADOOP-6269
> Project: Hadoop Common
> Issue Type: Bug
> Components: conf
> Affects Versions: 0.20.1
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Fix For: 0.20.2, 0.21.0
>
> Attachments: HADOOP-6269-1.patch, hadoop-6269.txt, hadoop-6269.txt
>
>
> Configuration.defaultResources is a simple ArrayList. In two places in
> Configuration it is accessed without appropriate synchronization, which we've
> seen to occasionally result in ConcurrentModificationExceptions.
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