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From "guangyi lu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-14073) DataNode runs async disk checks maybe throws NullPointerException, and DataNode failed to register to NameSpace.
Date Tue, 13 Nov 2018 12:37:00 GMT
guangyi lu created HDFS-14073:
---------------------------------

             Summary: DataNode runs async disk checks  maybe  throws NullPointerException,
and DataNode failed to register to NameSpace.
                 Key: HDFS-14073
                 URL: https://issues.apache.org/jira/browse/HDFS-14073
             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


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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