content: /*
   * Tencent is pleased to support the open source community by making Angel available.
   *
   * Copyright (C) 2017-2018 THL A29 Limited, a Tencent company. All rights reserved.
   *
   * Licensed 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
   *
   * https://opensource.org/licenses/Apache-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 com.tencent.angel.ipc;
  
  import com.tencent.angel.utils.Configurable;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.List;
  import java.util.concurrent.locks.ReentrantLock;
  
  /**
   * Base transport class used by ClientCache}.
   */
  public abstract class Transceiver implements Closeable, Configurable {
    private final ReentrantLock channelLock = new ReentrantLock();
  
    public abstract String getRemoteName() throws IOException;
  
    /**
     * Acquires an exclusive lock on the transceiver's channel.
     */
    public void lockChannel() {
      channelLock.lock();
    }
  
    /**
     * Releases the lock on the transceiver's channel if held by the calling thread.
     */
    public void unlockChannel() {
      if (channelLock.isHeldByCurrentThread()) {
        channelLock.unlock();
      }
    }
  
    /**
     * default calls {@link #writeBuffers(java.util.List)} followed by {@link #readBuffers()}.
     */
    public List<ByteBuffer> transceive(List<ByteBuffer> request) throws IOException {
      lockChannel();
      try {
        writeBuffers(request);
        return readBuffers();
      } finally {
        unlockChannel();
      }
    }
  
    /**
     * messages using callbacks.
     */
    public void transceive(List<ByteBuffer> request, Callback<List<ByteBuffer>> callback)
      throws IOException {
      // The default implementation works synchronously
      try {
        List<ByteBuffer> response = transceive(request);
        callback.handleResult(response);
      } catch (IOException e) {
        callback.handleError(e);
      }
    }
  
    /**
     * Called by the default definition of {@link #transceive(java.util.List)}.
     */
    public abstract List<ByteBuffer> readBuffers() throws IOException;
  
    public abstract void writeBuffers(List<ByteBuffer> buffers) throws IOException;
  
    /**
     * True if a handshake has been completed for this connection. Used to determine whether a
     * handshake need be completed prior to a one-way message. Requests and responses are always
     * prefixed by handshakes, but one-way messages. If the first request sent over a connection is
     * one-way, then a handshake-only response is returned. Subsequent one-way messages over the
     * connection will have no response data sent. Returns false by default.
     */
    public boolean isConnected() {
      return false;
    }
  
    public void close() throws IOException {
    }
  }
  