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From "Haohui Mai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9242) Fix Findbugs warning from webhdfs.DataNodeUGIProvider.ugiCache
Date Sun, 01 Nov 2015 18:31:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14984482#comment-14984482

Haohui Mai commented on HDFS-9242:

bq. I think the warning is false positive. We can write a filter rule in the dev-support/findbugsExcludeFile.xml

Findbug is right. The code is simply broken. It is possible to have multiple instances of
cache map.

bq. A correct way to fix is to make ugiCache volatile. Could you update it?

Fixing it with volatile is a bad idea as it bars many compiler optimization.

The suggested pattern is to do it through static initializer blocks, where the synchronization
is properly handled.

> Fix Findbugs warning from webhdfs.DataNodeUGIProvider.ugiCache 
> ---------------------------------------------------------------
>                 Key: HDFS-9242
>                 URL: https://issues.apache.org/jira/browse/HDFS-9242
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Xiaoyu Yao
>            Assignee: Brahma Reddy Battula
>         Attachments: HDFS-9242.patch
> This was introduced by HDFS-8855 and pre-patch warning can be found at https://builds.apache.org/job/PreCommit-HDFS-Build/12975/artifact/patchprocess/trunkFindbugsWarningshadoop-hdfs.html#DC_DOUBLECHECK
> {code}
> Code	Warning
> DC	Possible doublecheck on org.apache.hadoop.hdfs.server.datanode.web.webhdfs.DataNodeUGIProvider.ugiCache
in new org.apache.hadoop.hdfs.server.datanode.web.webhdfs.DataNodeUGIProvider(ParameterParser,
> Bug type DC_DOUBLECHECK (click for details) 
> In class org.apache.hadoop.hdfs.server.datanode.web.webhdfs.DataNodeUGIProvider
> In method new org.apache.hadoop.hdfs.server.datanode.web.webhdfs.DataNodeUGIProvider(ParameterParser,
> On field org.apache.hadoop.hdfs.server.datanode.web.webhdfs.DataNodeUGIProvider.ugiCache
> At DataNodeUGIProvider.java:[lines 49-51]
> {code}

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