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https://issues.apache.org/jira/browse/HDFS-7531?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lei (Eddy) Xu updated HDFS-7531:
--------------------------------
    Attachment: HDFS-7531.001.patch

Thanks for the reviews, [~cmccabe] and [~wheat9] !

I updated the patch to use {{compareAndSet}} instead of {{synchronized}} for 
{{addVolume}} and {{removeVolume}}.

Also changed to use JDK 7 features. 

> Improve the concurrent access on FsVolumeList
> ---------------------------------------------
>
>                 Key: HDFS-7531
>                 URL: https://issues.apache.org/jira/browse/HDFS-7531
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.6.0
>            Reporter: Lei (Eddy) Xu
>            Assignee: Lei (Eddy) Xu
>         Attachments: HDFS-7531.000.patch, HDFS-7531.001.patch
>
>
> {{FsVolumeList}} uses {{synchronized}} to protect the update on 
> {{FsVolumeList#volumes}}, while various operations (e.g., {{checkDirs()}}, 
> {{getAvailable()}}) iterate {{volumes}} without protection.
> This JIRA proposes to use {{AtomicReference}} to encapture {{volumes}} to 
> provide better concurrent access.



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