YARN-10460. Upgrading to JUnit 4.13 causes tests in TestNodeStatusUpdater to fail. Contributed by Peter Bacsko.

(cherry picked from commit bf0d058b698b15d1c51927b8fd8cf678ab95661a)

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

@@ -29,6 +29,8 @@ import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.io.ObjectWritable;
 import org.apache.hadoop.io.Writable;
 
+import com.google.common.annotations.VisibleForTesting;
+
 /* Cache a client using its socket factory as the hash key */
 @InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
 @InterfaceStability.Evolving
@@ -114,4 +116,10 @@ public class ClientCache {
       client.stop();
     }
   }
+
+  @VisibleForTesting
+  public void clearCache() {
+    clients.values().forEach(c -> c.stop());
+    clients.clear();
+  }
 }

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

@@ -335,7 +335,10 @@ public class ProtobufRpcEngine implements RpcEngine {
         RpcWritable.Buffer.class);
   }
   
- 
+  @VisibleForTesting
+  public static void clearClientCache() {
+    CLIENTS.clearCache();
+  }
 
   @Override
   public RPC.Server getServer(Class<?> protocol, Object protocolImpl,

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

@@ -52,6 +52,7 @@ import org.apache.hadoop.io.DataOutputBuffer;
 import org.apache.hadoop.io.Text;
 import org.apache.hadoop.io.retry.RetryPolicy;
 import org.apache.hadoop.io.retry.RetryProxy;
+import org.apache.hadoop.ipc.ProtobufRpcEngine;
 import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
 import org.apache.hadoop.net.NetUtils;
 import org.apache.hadoop.net.ServerSocketUtil;
@@ -122,6 +123,12 @@ public class TestNodeStatusUpdater extends NodeManagerTestBase {
   private NodeManager nm;
   private AtomicBoolean assertionFailedInThread = new AtomicBoolean(false);
 
+  @Before
+  public void before() {
+    // to avoid threading issues with JUnit 4.13+
+    ProtobufRpcEngine.clearClientCache();
+  }
+
   @After
   public void tearDown() {
     this.registeredNodes.clear();