HDFS-16040. RpcQueueTime metric counts requeued calls as unique events. Contributed by Simbarashe Dzinamarira.

(cherry picked from commit 8ce30f51f9)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java

@@ -2938,6 +2938,7 @@ public abstract class Server {
              */
             // Re-queue the call and continue
             requeueCall(call);
+            call = null;
             continue;
           }
           if (LOG.isDebugEnabled()) {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestConsistentReadsObserver.java

@@ -18,6 +18,8 @@
 package org.apache.hadoop.hdfs.server.namenode.ha;
 
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_STATE_CONTEXT_ENABLED_KEY;
+import static org.apache.hadoop.test.MetricsAsserts.getLongCounter;
+import static org.apache.hadoop.test.MetricsAsserts.getMetrics;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
@@ -28,6 +30,7 @@ import java.util.Collections;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
@@ -48,6 +51,7 @@ import org.apache.hadoop.ipc.RemoteException;
 import org.apache.hadoop.ipc.RpcScheduler;
 import org.apache.hadoop.ipc.Schedulable;
 import org.apache.hadoop.ipc.StandbyException;
+import org.apache.hadoop.metrics2.MetricsRecordBuilder;
 import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.util.Time;
 import org.junit.After;
@@ -419,6 +423,56 @@ public class TestConsistentReadsObserver {
     }
   }
 
+  @Test
+  public void testRpcQueueTimeNumOpsMetrics() throws Exception {
+    // 0 == not completed, 1 == succeeded, -1 == failed
+    AtomicInteger readStatus = new AtomicInteger(0);
+
+    // Making an uncoordinated call, which initialize the proxy
+    // to Observer node.
+    dfs.getClient().getHAServiceState();
+    dfs.mkdir(testPath, FsPermission.getDefault());
+    assertSentTo(0);
+
+    Thread reader = new Thread(new Runnable() {
+      @Override
+      public void run() {
+        try {
+          // this read will block until roll and tail edits happen.
+          dfs.getFileStatus(testPath);
+          readStatus.set(1);
+        } catch (IOException e) {
+          e.printStackTrace();
+          readStatus.set(-1);
+        }
+      }
+    });
+
+    reader.start();
+    // the reader is still blocking, not succeeded yet.
+    assertEquals(0, readStatus.get());
+    dfsCluster.rollEditLogAndTail(0);
+    // wait a while for all the change to be done
+    GenericTestUtils.waitFor(new Supplier<Boolean>() {
+      @Override
+      public Boolean get() {
+        return readStatus.get() != 0;
+      }
+    }, 100, 10000);
+    // the reader should have succeed.
+    assertEquals(1, readStatus.get());
+
+    final int observerIdx = 2;
+    NameNode observerNN = dfsCluster.getNameNode(observerIdx);
+    MetricsRecordBuilder rpcMetrics =
+        getMetrics("RpcActivityForPort"
+            + observerNN.getNameNodeAddress().getPort());
+    long rpcQueueTimeNumOps = getLongCounter("RpcQueueTimeNumOps", rpcMetrics);
+    long rpcProcessingTimeNumOps = getLongCounter("RpcProcessingTimeNumOps",
+        rpcMetrics);
+    assertEquals(rpcQueueTimeNumOps, rpcProcessingTimeNumOps);
+  }
+
   private void assertSentTo(int nnIdx) throws IOException {
     assertTrue("Request was not sent to the expected namenode " + nnIdx,
         HATestUtil.isSentToAnyOfNameNodes(dfs, dfsCluster, nnIdx));