From f59b698fc99211c010d569e7f71555183dfc29f1 Mon Sep 17 00:00:00 2001
From: Junping Du <junping_du@apache.org>
Date: Wed, 4 Feb 2015 19:10:52 -0800
Subject: [PATCH] HADOOP-10062. race condition in
 MetricsSystemImpl#publishMetricsNow that causes incorrect results. 
 (Contributed by Sangjin Lee) (cherry picked from commit
 0b567f424673b5cea1c3bc23b2bd268ef6b7625f)

---
 hadoop-common-project/hadoop-common/CHANGES.txt                | 3 +++
 .../org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java     | 2 +-
 .../org/apache/hadoop/metrics2/impl/TestMetricsSystemImpl.java | 2 +-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 05346f22f70..1eef93ee616 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -485,6 +485,9 @@ Release 2.7.0 - UNRELEASED
     HADOOP-11549. flaky test detection tool failed to handle special control
     characters in test result. (Yongjun Zhang via aajisaka)
 
+    HADOOP-10062. race condition in MetricsSystemImpl#publishMetricsNow that 
+    causes incorrect results. (Sangjin Lee via junping_du)
+
 Release 2.6.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java
index 4507e357957..b7660e5711c 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSystemImpl.java
@@ -387,7 +387,7 @@ public class MetricsSystemImpl extends MetricsSystem implements MetricsSource {
    * Requests an immediate publish of all metrics from sources to sinks.
    */
   @Override
-  public void publishMetricsNow() {
+  public synchronized void publishMetricsNow() {
     if (sinks.size() > 0) {
       publishMetrics(sampleMetrics(), true);
     }    
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/impl/TestMetricsSystemImpl.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/impl/TestMetricsSystemImpl.java
index d59e80b5820..4c2ebc8e0e8 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/impl/TestMetricsSystemImpl.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/impl/TestMetricsSystemImpl.java
@@ -190,7 +190,7 @@ public class TestMetricsSystemImpl {
       threads[i] = new Thread(new Runnable() {
         private boolean safeAwait(int mySource, CyclicBarrier barrier) {
           try {
-            barrier1.await(2, TimeUnit.SECONDS);
+            barrier.await(2, TimeUnit.SECONDS);
           } catch (InterruptedException e) {
             results[mySource] = "Interrupted";
             return false;