From 645d67bc4f4e29d10ef810386c89e6a7c8c61862 Mon Sep 17 00:00:00 2001
From: Wei-Chiu Chuang <weichiu@apache.org>
Date: Fri, 21 Jun 2019 18:27:03 -0700
Subject: [PATCH] HDFS-14074. DataNode runs async disk checks maybe throws
 NullPointerException, and DataNode failed to register to NameSpace. 
 Contributed by guangyi lu.

---
 .../hdfs/server/datanode/checker/ThrottledAsyncChecker.java   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/checker/ThrottledAsyncChecker.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/checker/ThrottledAsyncChecker.java
index 88444539337..032379a4d12 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/checker/ThrottledAsyncChecker.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/checker/ThrottledAsyncChecker.java
@@ -123,8 +123,8 @@ public class ThrottledAsyncChecker<K, V> implements AsyncChecker<K, V> {
       return Optional.empty();
     }
 
-    if (completedChecks.containsKey(target)) {
-      final LastCheckResult<V> result = completedChecks.get(target);
+    final LastCheckResult<V> result = completedChecks.get(target);
+    if (result != null) {
       final long msSinceLastCheck = timer.monotonicNow() - result.completedAt;
       if (msSinceLastCheck < minMsBetweenChecks) {
         LOG.debug("Skipped checking {}. Time since last check {}ms " +