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Date: Wed, 23 Nov 2011 21:40:40 +0000 (UTC)
From: "Daryn Sharp (Commented) (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HADOOP-7854) UGI getCurrentUser is not
 synchronized
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    [ https://issues.apache.org/jira/browse/HADOOP-7854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13156307#comment-13156307 ] 

Daryn Sharp commented on HADOOP-7854:
-------------------------------------

Per Kihwal's comment, the exception occurs when two unsynchronized callers attempt to use the {{Subject}} from the current context.
                
> UGI getCurrentUser is not synchronized
> --------------------------------------
>
>                 Key: HADOOP-7854
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7854
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: security
>    Affects Versions: 0.20.205.1
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>         Attachments: HADOOP-7854.patch
>
>
> Sporadic {{ConcurrentModificationExceptions}} are originating from {{UGI.getCurrentUser}} when it needs to create a new instance.  The problem was specifically observed in a JT under heavy load when a post-job cleanup is accessing the UGI while a new job is being processed.

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