YARN-9639. DecommissioningNodesWatcher cause memory leak. Contributed by Bilwa S T.

(cherry picked from commit be80334cdf255616f589217726483194fb56dcc6)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/DecommissioningNodesWatcher.java

@@ -207,6 +207,11 @@ public class DecommissioningNodesWatcher {
     }
   }
 
+  public void stop() {
+    pollTimer.cancel();
+    pollTimer = null;
+  }
+
   /**
    * Status about a specific decommissioning node.
    *

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/ResourceTrackerService.java

@@ -263,6 +263,7 @@ public class ResourceTrackerService extends AbstractService implements
 
   @Override
   protected void serviceStop() throws Exception {
+    decommissioningWatcher.stop();
     if (this.server != null) {
       this.server.stop();
     }