From 14b3c2695b152285ed2919f2aa5a25e247c47871 Mon Sep 17 00:00:00 2001
From: John Zhuge <jzhuge@cloudera.com>
Date: Mon, 16 Oct 2017 13:29:29 -0700
Subject: [PATCH] HADOOP-14954. MetricsSystemImpl#init should increment
 refCount when already initialized. Contributed by John Zhuge.

---
 .../metrics2/impl/MetricsSystemImpl.java      | 12 ++++-
 .../metrics2/impl/TestMetricsSystemImpl.java  | 46 +++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

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 ee1672ef0c3..c507a77a996 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
@@ -140,6 +140,16 @@ public class MetricsSystemImpl extends MetricsSystem implements MetricsSource {
     this(null);
   }
 
+  @VisibleForTesting
+  boolean isMonitoring() {
+    return monitoring;
+  }
+
+  @VisibleForTesting
+  int getRefCount() {
+    return refCount;
+  }
+
   /**
    * Initialized the metrics system with a prefix.
    * @param prefix  the system will look for configs with the prefix
@@ -147,12 +157,12 @@ public class MetricsSystemImpl extends MetricsSystem implements MetricsSource {
    */
   @Override
   public synchronized MetricsSystem init(String prefix) {
+    ++refCount;
     if (monitoring && !DefaultMetricsSystem.inMiniClusterMode()) {
       LOG.warn(this.prefix +" metrics system already initialized!");
       return this;
     }
     this.prefix = checkNotNull(prefix, "prefix");
-    ++refCount;
     if (monitoring) {
       // in mini cluster mode
       LOG.info(this.prefix +" metrics system started (again)");
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 abd1b132b0a..879de2d0a19 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
@@ -26,6 +26,8 @@ import java.util.concurrent.atomic.*;
 
 import javax.annotation.Nullable;
 
+import org.hamcrest.CoreMatchers;
+import org.junit.Assert;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
@@ -559,6 +561,50 @@ public class TestMetricsSystemImpl {
     ms.shutdown();
   }
 
+  @Test
+  public void testInitShutdown() {
+    boolean oldMode = DefaultMetricsSystem.inMiniClusterMode();
+    try {
+      DefaultMetricsSystem.setMiniClusterMode(true);
+      runInitShutdownTests();
+
+      DefaultMetricsSystem.setMiniClusterMode(false);
+      runInitShutdownTests();
+    } finally {
+      DefaultMetricsSystem.setMiniClusterMode(oldMode);
+    }
+  }
+
+  private void runInitShutdownTests() {
+    MetricsSystemImpl ms = new MetricsSystemImpl();
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(false));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(0));
+
+    ms.init("TestMetricsSystem1");
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(true));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(1));
+
+    ms.shutdown();
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(false));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(0));
+
+    ms.init("TestMetricsSystem2");
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(true));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(1));
+
+    ms.init("TestMetricsSystem3");
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(true));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(2));
+
+    ms.shutdown();
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(true));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(1));
+
+    ms.shutdown();
+    Assert.assertThat(ms.isMonitoring(), CoreMatchers.is(false));
+    Assert.assertThat(ms.getRefCount(), CoreMatchers.is(0));
+  }
+
   @Metrics(context="test")
   private static class TestSource {
     @Metric("C1 desc") MutableCounterLong c1;