HDFS-10915. Fix time measurement bug in TestDatanodeRestart. Contributed by Xiaobing Zhou

(cherry picked from commit 6437ba18c5c26bc271a63aff5ea03756f43dd9a3)

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestDatanodeRestart.java

@@ -45,6 +45,7 @@ import org.apache.hadoop.hdfs.server.datanode.ReplicaInfo;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
 import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.util.Time;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -172,17 +173,17 @@ public class TestDatanodeRestart {
       cluster = new MiniDFSCluster.Builder(conf).numDataNodes(numDNs).build();
       cluster.waitActive();
 
-      start = System.currentTimeMillis();
+      start = Time.monotonicNow();
       FileSystem fileSys = cluster.getFileSystem();
       try {
         DFSTestUtil.createFile(fileSys, file, 10240L, (short)1, 0L);
         // It is a bug if this does not fail.
         throw new IOException("Did not fail!");
       } catch (org.apache.hadoop.ipc.RemoteException e) {
-        long elapsed = System.currentTimeMillis() - start;
+        long elapsed = Time.monotonicNow() - start;
         // timers have at-least semantics, so it should be at least 5 seconds.
         if (elapsed < 5000 || elapsed > 10000) {
-          throw new IOException(elapsed + " seconds passed.", e);
+          throw new IOException(elapsed + " milliseconds passed.", e);
         }
       }
       DataNodeFaultInjector.set(oldDnInjector);
@@ -195,18 +196,18 @@ public class TestDatanodeRestart {
       // back to simulating unregistered node.
       DataNodeFaultInjector.set(dnFaultInjector);
       byte[] buffer = new byte[8];
-      start = System.currentTimeMillis();
+      start = Time.monotonicNow();
       try {
         fileSys.open(file).read(0L, buffer, 0, 1);
         throw new IOException("Did not fail!");
       } catch (IOException e) {
-        long elapsed = System.currentTimeMillis() - start;
+        long elapsed = Time.monotonicNow() - start;
         if (e.getMessage().contains("readBlockLength")) {
           throw new IOException("Failed, but with unexpected exception:", e);
         }
         // timers have at-least semantics, so it should be at least 5 seconds.
         if (elapsed < 5000 || elapsed > 10000) {
-          throw new IOException(elapsed + " seconds passed.", e);
+          throw new IOException(elapsed + " milliseconds passed.", e);
         }
       }
       DataNodeFaultInjector.set(oldDnInjector);