content: /*
   * 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.spark.launcher;
  
  import java.io.Closeable;
  import java.io.EOFException;
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.net.Socket;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import static org.apache.spark.launcher.LauncherProtocol.*;
  
  /**
   * Encapsulates a connection between a launcher server and client. This takes care of the
   * communication (sending and receiving messages), while processing of messages is left for
   * the implementations.
   */
  abstract class LauncherConnection implements Closeable, Runnable {
  
    private static final Logger LOG = Logger.getLogger(LauncherConnection.class.getName());
  
    private final Socket socket;
    private final ObjectOutputStream out;
  
    private volatile boolean closed;
  
    LauncherConnection(Socket socket) throws IOException {
      this.socket = socket;
      this.out = new ObjectOutputStream(socket.getOutputStream());
      this.closed = false;
    }
  
    protected abstract void handle(Message msg) throws IOException;
  
    @Override
    public void run() {
      try {
        ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
        while (!closed) {
          Message msg = (Message) in.readObject();
          handle(msg);
        }
      } catch (EOFException eof) {
        // Remote side has closed the connection, just cleanup.
        try {
          close();
        } catch (Exception unused) {
          // no-op.
        }
      } catch (Exception e) {
        if (!closed) {
          LOG.log(Level.WARNING, "Error in inbound message handling.", e);
          try {
            close();
          } catch (Exception unused) {
            // no-op.
          }
        }
      }
    }
  
    protected synchronized void send(Message msg) throws IOException {
      try {
        CommandBuilderUtils.checkState(!closed, "Disconnected.");
        out.writeObject(msg);
        out.flush();
      } catch (IOException ioe) {
        if (!closed) {
          LOG.log(Level.WARNING, "Error when sending message.", ioe);
          try {
            close();
          } catch (Exception unused) {
            // no-op.
          }
        }
        throw ioe;
      }
    }
  
    @Override
    public void close() throws IOException {
      if (!closed) {
        synchronized (this) {
          if (!closed) {
            closed = true;
            socket.close();
          }
        }
      }
    }
  
  }
  