YARN-7602. NM should reference the singleton JvmMetrics instance.

(cherry picked from commit 2f6c038be6c23522ea64fc4e415910fb72493eb2)

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/source/TestJvmMetrics.java

@@ -200,4 +200,30 @@ public void alert(GcTimeMonitor.GcData gcData) {
     Assert.assertTrue(alerter.numAlerts > 0);
     Assert.assertTrue(alerter.maxGcTimePercentage >= alertGcPerc);
   }
+
+  @Test
+  public void testJvmMetricsSingletonWithSameProcessName() {
+    JvmMetrics jvmMetrics1 = org.apache.hadoop.metrics2.source.JvmMetrics
+        .initSingleton("test", null);
+    JvmMetrics jvmMetrics2 = org.apache.hadoop.metrics2.source.JvmMetrics
+        .initSingleton("test", null);
+    Assert.assertEquals("initSingleton should return the singleton instance",
+        jvmMetrics1, jvmMetrics2);
+  }
+
+  @Test
+  public void testJvmMetricsSingletonWithDifferentProcessNames() {
+    final String process1Name = "process1";
+    JvmMetrics jvmMetrics1 = org.apache.hadoop.metrics2.source.JvmMetrics
+        .initSingleton(process1Name, null);
+    final String process2Name = "process2";
+    JvmMetrics jvmMetrics2 = org.apache.hadoop.metrics2.source.JvmMetrics
+        .initSingleton(process2Name, null);
+    Assert.assertEquals("initSingleton should return the singleton instance",
+        jvmMetrics1, jvmMetrics2);
+    Assert.assertEquals("unexpected process name of the singleton instance",
+        process1Name, jvmMetrics1.processName);
+    Assert.assertEquals("unexpected process name of the singleton instance",
+        process1Name, jvmMetrics2.processName);
+  }
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/metrics/NodeManagerMetrics.java

@@ -86,7 +86,7 @@ public class NodeManagerMetrics {
   private long availableMB;
   private long allocatedOpportunisticMB;
 
-  public NodeManagerMetrics(JvmMetrics jvmMetrics) {
+  private NodeManagerMetrics(JvmMetrics jvmMetrics) {
     this.jvmMetrics = jvmMetrics;
   }
 
@@ -94,8 +94,8 @@ public static NodeManagerMetrics create() {
     return create(DefaultMetricsSystem.instance());
   }
 
-  static NodeManagerMetrics create(MetricsSystem ms) {
+  private static NodeManagerMetrics create(MetricsSystem ms) {
-    JvmMetrics jm = JvmMetrics.create("NodeManager", null, ms);
+    JvmMetrics jm = JvmMetrics.initSingleton("NodeManager", null);
     return ms.register(new NodeManagerMetrics(jm));
   }
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/test/java/org/apache/hadoop/yarn/server/nodemanager/metrics/TestNodeManagerMetrics.java

@@ -19,19 +19,40 @@
 
 import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
 import org.apache.hadoop.metrics2.MetricsRecordBuilder;
+import org.apache.hadoop.metrics2.source.JvmMetrics;
 import static org.apache.hadoop.test.MetricsAsserts.*;
 import org.apache.hadoop.yarn.api.records.Resource;
 import org.apache.hadoop.yarn.util.Records;
 
+import org.junit.After;
 import org.junit.Assert;
+import org.junit.Before;
 import org.junit.Test;
 
 public class TestNodeManagerMetrics {
   static final int GiB = 1024; // MiB
 
-  @Test public void testNames() {
+  private NodeManagerMetrics metrics;
+
+  @Before
+  public void setup() {
     DefaultMetricsSystem.initialize("NodeManager");
-    NodeManagerMetrics metrics = NodeManagerMetrics.create();
+    metrics = NodeManagerMetrics.create();
+  }
+
+  @After
+  public void tearDown() {
+    DefaultMetricsSystem.shutdown();
+  }
+
+  @Test
+  public void testReferenceOfSingletonJvmMetrics()  {
+    JvmMetrics jvmMetrics = JvmMetrics.initSingleton("NodeManagerModule", null);
+    Assert.assertEquals("NodeManagerMetrics should reference the singleton" +
+        " JvmMetrics instance", jvmMetrics, metrics.getJvmMetrics());
+  }
+
+  @Test public void testNames() {
     Resource total = Records.newRecord(Resource.class);
     total.setMemorySize(8*GiB);
     total.setVirtualCores(16);