[jira] [Created] (HDFS-14072) DataNode runs async disk checks maybe throws NullPointerException, and DataNode failed to register to NameSpace.

["guangyi lu (JIRA)" <ji...@apache.org>]

guangyi lu created HDFS-14072:
---------------------------------

             Summary: 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: 3.0.0, 2.8.0
         Environment: hadoop-2.7.3, hadoop-2.8.0
            Reporter: guangyi lu
         Attachments: image-2018-11-13-20-23-22-138.png, image-2018-11-13-20-23-26-813.png

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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