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https://issues.apache.org/jira/browse/HDFS-14072?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Arpit Agarwal resolved HDFS-14072.
----------------------------------
    Resolution: Duplicate

Resolving as a dup since you have posted a patch on HDFS-14074.

> DataNode runs async disk checks  maybe  throws NullPointerException, and 
> DataNode failed to register to NameSpace.
> ------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-14072
>                 URL: https://issues.apache.org/jira/browse/HDFS-14072
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs
>    Affects Versions: 2.8.0, 3.0.0
>         Environment: hadoop-2.7.3, hadoop-2.8.0
>            Reporter: guangyi lu
>            Priority: Major
>              Labels: HDFS, HDFS-11114
>         Attachments: image-2018-11-13-20-23-22-138.png, 
> image-2018-11-13-20-23-26-813.png
>
>   Original Estimate: 48h
>  Remaining Estimate: 48h
>
> In ThrottledAsyncChecker class,it members of the completedChecks is 
> WeakHashMap, its definition is as follows:
>      this.completedChecks = new WeakHashMap<>();
> and one of its uses is as follows in schedule method:
>     if (completedChecks.containsKey(target)) {
>         // here may be happen garbage collection,and result may be null.
>          final LastCheckResult<V> result = completedChecks.get(target);
>          final long msSinceLastCheck = timer.monotonicNow() - 
> result.completedAt;
>     }
> after  "completedChecks.containsKey(target)",  may be happen garbage 
> collection,  and result may be null.
>  
> !image-2018-11-13-20-23-26-813.png!



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