guangyi lu created HDFS-14074:
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Summary: 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: 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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