HADOOP-12259. Utility to Dynamic port allocation (brahmareddy via rkanter)

(cherry picked from commit ee233ec95ce8cfc8309d3adc072d926cd85eba08)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -217,6 +217,8 @@ Release 2.8.0 - UNRELEASED
     HADOOP-12189. Improve CallQueueManager#swapQueue to make queue elements
     drop nearly impossible. (Zhihai Xu via wang)
 
+    HADOOP-12259. Utility to Dynamic port allocation (brahmareddy via rkanter)
+
   OPTIMIZATIONS
 
     HADOOP-11785. Reduce the number of listStatus operation in distcp

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/ServerSocketUtil.java

@@ -0,0 +1,63 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.net;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.util.Random;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+public class ServerSocketUtil {
+
+  private static final Log LOG = LogFactory.getLog(ServerSocketUtil.class);
+
+  /**
+   * Port scan & allocate is how most other apps find ports
+   * 
+   * @param port given port
+   * @param retries number of retires
+   * @return
+   * @throws IOException
+   */
+  public static int getPort(int port, int retries) throws IOException {
+    Random rand = new Random();
+    int tryPort = port;
+    int tries = 0;
+    while (true) {
+      if (tries > 0) {
+        tryPort = port + rand.nextInt(65535 - port);
+      }
+      LOG.info("Using port " + tryPort);
+      try (ServerSocket s = new ServerSocket(tryPort)) {
+        return tryPort;
+      } catch (IOException e) {
+        tries++;
+        if (tries >= retries) {
+          LOG.info("Port is already in use; giving up");
+          throw e;
+        } else {
+          LOG.info("Port is already in use; trying again");
+        }
+      }
+    }
+  }
+
+}