HDFS-8896. DataNode object isn't GCed when shutdown, because it has GC root in ShutdownHookManager. Contributed by Walter Su.

(cherry picked from commit f44b599003bb79b1ec9b92e7546546523ec01676)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ShutdownHookManager.java

@@ -187,4 +187,10 @@ public class ShutdownHookManager {
     return shutdownInProgress.get();
   }
 
+  /**
+   * clear all registered shutdownHooks.
+   */
+  public void clearShutdownHooks() {
+    hooks.clear();
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -496,6 +496,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-8951. Move the shortcircuit package to hdfs-client.
     (Mingliang Liu via wheat9)
 
+    HDFS-8896. DataNode object isn't GCed when shutdown, because it has GC
+    root in ShutdownHookManager. (Walter Su via jing9)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java

@@ -119,6 +119,7 @@ import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.security.authorize.ProxyUsers;
 import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.util.ExitUtil;
+import org.apache.hadoop.util.ShutdownHookManager;
 import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.util.ToolRunner;
 
@@ -1759,6 +1760,7 @@ public class MiniDFSCluster {
         nameNode = null;
       }
     }
+    ShutdownHookManager.get().clearShutdownHooks();
     if (base_dir != null) {
       if (deleteDfsDir) {
         base_dir.delete();