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.guacamole.net;
  
  
  import java.util.concurrent.locks.ReentrantLock;
  import org.apache.guacamole.GuacamoleException;
  import org.apache.guacamole.io.GuacamoleReader;
  import org.apache.guacamole.io.GuacamoleWriter;
  
  /**
   * Base GuacamoleTunnel implementation which synchronizes access to the
   * underlying reader and writer with reentrant locks. Implementations need only
   * provide the tunnel's UUID and socket.
   *
   * @author Michael Jumper
   */
  public abstract class AbstractGuacamoleTunnel implements GuacamoleTunnel {
  
      /**
       * Lock acquired when a read operation is in progress.
       */
      private final ReentrantLock readerLock;
  
      /**
       * Lock acquired when a write operation is in progress.
       */
      private final ReentrantLock writerLock;
  
      /**
       * Creates a new GuacamoleTunnel which synchronizes access to the
       * Guacamole instruction stream associated with the underlying
       * GuacamoleSocket.
       */
      public AbstractGuacamoleTunnel() {
          readerLock = new ReentrantLock();
          writerLock = new ReentrantLock();
      }
  
      /**
       * Acquires exclusive read access to the Guacamole instruction stream
       * and returns a GuacamoleReader for reading from that stream.
       *
       * @return A GuacamoleReader for reading from the Guacamole instruction
       *         stream.
       */
      @Override
      public GuacamoleReader acquireReader() {
          readerLock.lock();
          return getSocket().getReader();
      }
  
      /**
       * Relinquishes exclusive read access to the Guacamole instruction
       * stream. This function should be called whenever a thread finishes using
       * a GuacamoleTunnel's GuacamoleReader.
       */
      @Override
      public void releaseReader() {
          readerLock.unlock();
      }
  
      /**
       * Returns whether there are threads waiting for read access to the
       * Guacamole instruction stream.
       *
       * @return true if threads are waiting for read access the Guacamole
       *         instruction stream, false otherwise.
       */
      @Override
      public boolean hasQueuedReaderThreads() {
          return readerLock.hasQueuedThreads();
      }
  
      /**
       * Acquires exclusive write access to the Guacamole instruction stream
       * and returns a GuacamoleWriter for writing to that stream.
       *
       * @return A GuacamoleWriter for writing to the Guacamole instruction
       *         stream.
       */
      @Override
      public GuacamoleWriter acquireWriter() {
          writerLock.lock();
          return getSocket().getWriter();
      }
  
      /**
       * Relinquishes exclusive write access to the Guacamole instruction
       * stream. This function should be called whenever a thread finishes using
       * a GuacamoleTunnel's GuacamoleWriter.
       */
      @Override
      public void releaseWriter() {
          writerLock.unlock();
      }
  
      @Override
      public boolean hasQueuedWriterThreads() {
          return writerLock.hasQueuedThreads();
      }
  
      @Override
      public void close() throws GuacamoleException {
          getSocket().close();
      }
  
      @Override
      public boolean isOpen() {
          return getSocket().isOpen();
      }
  
  }
  