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https://issues.apache.org/jira/browse/HDFS-11267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15781739#comment-15781739
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Manoj Govindassamy commented on HDFS-11267:
-------------------------------------------
The fix for HDFS-11251 (ConcurrentModificationException during
DataNode#refreshVolumes) making the {{Storage#storageDirs}} a
{{CopyOnWriteArrayList}} is needed for this bug. On top of HDFS-11251 fix, we
need more clean up patches.
> Avoid redefinition of storageDirs in NNStorage and cleanup its accessors in
> Storage
> -----------------------------------------------------------------------------------
>
> Key: HDFS-11267
> URL: https://issues.apache.org/jira/browse/HDFS-11267
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.0.0-alpha1
> Reporter: Manoj Govindassamy
> Assignee: Manoj Govindassamy
>
> In the abstract class {{Storage}}, {{storageDirs}} is a protected variable
> and all its derived classes like {{NNStorage}}, {{JNStorage}},
> {{DataStorage}}.. are iterating over this non-thread safe variable without
> any proper locks. Any parallel modification operation like add or remove
> volume can mutate the backing storageDirs list and any iterators on this list
> around the same time can face {{ConcurrentModificationException}}. It would
> be good to make the variable private and restrict the access via getters and
> setters. Any thread safe restriction need to be done can then be placed on
> the parent class only.
> Also, {{NNStorage}} redefines parent class Storage's {{storageDirs}}, making
> it inconsistent with other derived classes. Would be cleaner if {{NNStorage}}
> can avoid re-defining it locally.
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