From 68164b197b4619235fa46bf5600e6fe815ef1410 Mon Sep 17 00:00:00 2001
From: Jing Zhao <jing9@apache.org>
Date: Fri, 20 Dec 2013 22:08:53 +0000
Subject: [PATCH] HADOOP-10169. Merge change r1552820 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1552822 13f79535-47bb-0310-9956-ffa450edef68
---
 .../hadoop-common/CHANGES.txt                 |  3 +++
 .../hadoop/metrics2/source/JvmMetrics.java    | 19 +++++++++++--------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 2b4fa3462eb..67c6d700505 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -109,6 +109,9 @@ Release 2.4.0 - UNRELEASED
 
     HADOOP-10164. Allow UGI to login with a known Subject (bobby)
 
+    HADOOP-10169. Remove the unnecessary synchronized in JvmMetrics class.
+    (Liang Xie via jing9) 
+
   OPTIMIZATIONS
 
     HADOOP-9748. Reduce blocking on UGI.ensureInitialized (daryn)
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/source/JvmMetrics.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/source/JvmMetrics.java
index 35c92bbe92c..750499139a6 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/source/JvmMetrics.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/source/JvmMetrics.java
@@ -24,10 +24,8 @@ import java.lang.management.MemoryUsage;
 import java.lang.management.ThreadInfo;
 import java.lang.management.ThreadMXBean;
 import java.lang.management.GarbageCollectorMXBean;
-import java.util.Map;
 import java.util.List;
-
-import com.google.common.collect.Maps;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.log.metrics.EventCounter;
@@ -67,7 +65,8 @@ public class JvmMetrics implements MetricsSource {
       ManagementFactory.getGarbageCollectorMXBeans();
   final ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();
   final String processName, sessionId;
-  final Map<String, MetricsInfo[]> gcInfoCache = Maps.newHashMap();
+  final ConcurrentHashMap<String, MetricsInfo[]> gcInfoCache =
+      new ConcurrentHashMap<String, MetricsInfo[]>();
 
   JvmMetrics(String processName, String sessionId) {
     this.processName = processName;
@@ -123,13 +122,17 @@ public class JvmMetrics implements MetricsSource {
       .addCounter(GcTimeMillis, timeMillis);
   }
 
-  private synchronized MetricsInfo[] getGcInfo(String gcName) {
+  private MetricsInfo[] getGcInfo(String gcName) {
     MetricsInfo[] gcInfo = gcInfoCache.get(gcName);
     if (gcInfo == null) {
       gcInfo = new MetricsInfo[2];
-      gcInfo[0] = Interns.info("GcCount"+ gcName, "GC Count for "+ gcName);
-      gcInfo[1] = Interns.info("GcTimeMillis"+ gcName, "GC Time for "+ gcName);
-      gcInfoCache.put(gcName, gcInfo);
+      gcInfo[0] = Interns.info("GcCount" + gcName, "GC Count for " + gcName);
+      gcInfo[1] = Interns
+          .info("GcTimeMillis" + gcName, "GC Time for " + gcName);
+      MetricsInfo[] previousGcInfo = gcInfoCache.putIfAbsent(gcName, gcInfo);
+      if (previousGcInfo != null) {
+        return previousGcInfo;
+      }
     }
     return gcInfo;
   }