YARN-8183. Fix ConcurrentModificationException inside RMAppAttemptMetrics#convertAtomicLongMaptoLongMap. (Suma Shivaprasad via wangda)

Change-Id: I347871d672001653a3afe2e99adefd74e0d798cd
(cherry picked from commit bb3c504764f807fccba7f28298a12e2296f284cb)
(cherry picked from commit 3043a93d461fd8b9ccc2ff4b8d17e5430ed77615)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmapp/attempt/RMAppAttemptMetrics.java

@@ -20,6 +20,7 @@ package org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt;
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
@@ -53,8 +54,8 @@ public class RMAppAttemptMetrics {
   
   private ReadLock readLock;
   private WriteLock writeLock;
-  private Map<String, AtomicLong> resourceUsageMap = new HashMap<>();
-  private Map<String, AtomicLong> preemptedResourceMap = new HashMap<>();
+  private Map<String, AtomicLong> resourceUsageMap = new ConcurrentHashMap<>();
+  private Map<String, AtomicLong> preemptedResourceMap = new ConcurrentHashMap<>();
   private RMContext rmContext;
 
   private int[][] localityStatistics =
@@ -97,7 +98,7 @@ public class RMAppAttemptMetrics {
   public Resource getResourcePreempted() {
     try {
       readLock.lock();
-      return resourcePreempted;
+      return Resource.newInstance(resourcePreempted);
     } finally {
       readLock.unlock();
     }
@@ -229,7 +230,7 @@ public class RMAppAttemptMetrics {
   }
 
   public Resource getApplicationAttemptHeadroom() {
-    return applicationHeadroom;
+    return Resource.newInstance(applicationHeadroom);
   }
 
   public void setApplicationAttemptHeadRoom(Resource headRoom) {