[jira] [Commented] (HDFS-14074) DataNode runs async disk checks maybe throws NullPointerException, and DataNode failed to register to NameSpace.

["Hadoop QA (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-14074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16685150#comment-16685150 ] 

Hadoop QA commented on HDFS-14074:
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:blue}0{color} | {color:blue} reexec {color} | {color:blue}  0m  0s{color} | {color:blue} Docker mode activated. {color} |
| {color:red}-1{color} | {color:red} patch {color} | {color:red}  0m  5s{color} | {color:red} HDFS-14074 does not apply to trunk. Rebase required? Wrong Branch? See https://wiki.apache.org/hadoop/HowToContribute for help. {color} |
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|| Subsystem || Report/Notes ||
| JIRA Issue | HDFS-14074 |
| JIRA Patch URL | https://issues.apache.org/jira/secure/attachment/12947976/HDFS-14074.patch |
| Console output | https://builds.apache.org/job/PreCommit-HDFS-Build/25503/console |
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> DataNode runs async disk checks  maybe  throws NullPointerException, and DataNode failed to register to NameSpace.
> ------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-14074
>                 URL: https://issues.apache.org/jira/browse/HDFS-14074
>             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
>             Fix For: 2.8.0, 2.7.3, 3.0.0
>
>         Attachments: HDFS-14074.patch, WechatIMG83.jpeg
>
>   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.
> the solution is：
> this.completedChecks = new ReferenceMap(1, 1);
> or
>  this.completedChecks = new HashMap<>();
>  



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