From 8db9d61ac2e04888cb228b29fe54b41c730cf0e6 Mon Sep 17 00:00:00 2001
From: Daniel Templeton <templedf@apache.org>
Date: Tue, 7 Nov 2017 14:53:48 -0800
Subject: [PATCH] YARN-7401. Reduce lock contention in
 ClusterNodeTracker#getClusterCapacity()

---
 .../scheduler/ClusterNodeTracker.java          | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/ClusterNodeTracker.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/ClusterNodeTracker.java
index ccec6bc6a8..60ef390a3b 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/ClusterNodeTracker.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/ClusterNodeTracker.java
@@ -55,8 +55,9 @@ public class ClusterNodeTracker<N extends SchedulerNode> {
   private Map<String, N> nodeNameToNodeMap = new HashMap<>();
   private Map<String, List<N>> nodesPerRack = new HashMap<>();
 
-  private Resource clusterCapacity = Resources.clone(Resources.none());
-  private Resource staleClusterCapacity = null;
+  private final Resource clusterCapacity = Resources.clone(Resources.none());
+  private volatile Resource staleClusterCapacity =
+      Resources.clone(Resources.none());
 
   // Max allocation
   private long maxNodeMemory = -1;
@@ -82,6 +83,7 @@ public void addNode(N node) {
 
       // Update cluster capacity
       Resources.addTo(clusterCapacity, node.getTotalResource());
+      staleClusterCapacity = Resources.clone(clusterCapacity);
 
       // Update maximumAllocation
       updateMaxResources(node, true);
@@ -139,16 +141,7 @@ public int nodeCount(String rackName) {
   }
 
   public Resource getClusterCapacity() {
-    readLock.lock();
-    try {
-      if (staleClusterCapacity == null ||
-          !Resources.equals(staleClusterCapacity, clusterCapacity)) {
-        staleClusterCapacity = Resources.clone(clusterCapacity);
-      }
-      return staleClusterCapacity;
-    } finally {
-      readLock.unlock();
-    }
+    return staleClusterCapacity;
   }
 
   public N removeNode(NodeId nodeId) {
@@ -175,6 +168,7 @@ public N removeNode(NodeId nodeId) {
 
       // Update cluster capacity
       Resources.subtractFrom(clusterCapacity, node.getTotalResource());
+      staleClusterCapacity = Resources.clone(clusterCapacity);
 
       // Update maximumAllocation
       updateMaxResources(node, false);