HDDS-1332. Attempt to fix flaky test testStartStopDatanodeStateMachine (#697)

hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/statemachine/SCMConnectionManager.java

@@ -35,13 +35,13 @@ import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 
+import static java.util.Collections.unmodifiableList;
 import static org.apache.hadoop.hdds.scm.HddsServerUtil
     .getScmRpcTimeOutInMilliseconds;
 
@@ -184,7 +184,12 @@ public class SCMConnectionManager
    * @return - List of RPC Endpoints.
    */
   public Collection<EndpointStateMachine> getValues() {
-    return scmMachines.values();
+    readLock();
+    try {
+      return unmodifiableList(new ArrayList<>(scmMachines.values()));
+    } finally {
+      readUnlock();
+    }
   }
 
   @Override
@@ -201,9 +206,7 @@ public class SCMConnectionManager
   public List<EndpointStateMachineMBean> getSCMServers() {
     readLock();
     try {
-      return Collections
-          .unmodifiableList(new ArrayList<>(scmMachines.values()));
-
+      return unmodifiableList(new ArrayList<>(scmMachines.values()));
     } finally {
       readUnlock();
     }

hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/TestDatanodeStateMachine.java

@@ -154,8 +154,6 @@ public class TestDatanodeStateMachine {
 
   /**
    * Assert that starting statemachine executes the Init State.
-   *
-   * @throws InterruptedException
    */
   @Test
   public void testStartStopDatanodeStateMachine() throws IOException,
@@ -167,9 +165,9 @@ public class TestDatanodeStateMachine {
           stateMachine.getConnectionManager();
       GenericTestUtils.waitFor(
           () -> {
-            LOG.info("connectionManager.getValues().size() is {}",
-                connectionManager.getValues().size());
-            return connectionManager.getValues().size() == 1;
+            int size = connectionManager.getValues().size();
+            LOG.info("connectionManager.getValues().size() is {}", size);
+            return size == 1;
           }, 1000, 30000);
 
       stateMachine.stopDaemon();