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 com.alibaba.wasp.ipc;
  
  import com.alibaba.wasp.FConstants;
  import org.apache.hadoop.conf.Configuration;
  
  import javax.net.SocketFactory;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.net.InetSocketAddress;
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * Cache a client using its socket factory as the hash key. Enables
   * reuse/sharing of clients on a per SocketFactory basis. A client establishes
   * certain configuration dependent characteristics like timeouts, tcp-keepalive
   * (true or false), etc. For more details on the characteristics. Creation of
   * dynamic proxies to protocols creates the clients (and increments reference
   * count once created), and stopping of the proxies leads to clearing out
   * references and when the reference drops to zero, the cache mapping is
   * cleared.
   */
  class ClientCache {
    private Map<String, NettyTransceiver> clients = new HashMap<String, NettyTransceiver>();
  
    protected ClientCache() {
    }
  
    /**
     * Construct & cache an IPC client with the user-provided SocketFactory if no
     * cached client exists.
     * 
     * @param conf
     *          Configuration
     * @param factory
     *          socket factory
     * @return an IPC client
     */
    protected synchronized NettyTransceiver getClient(InetSocketAddress addr,
        SocketFactory factory, Configuration conf) {
  
      NettyTransceiver client = clients.get(addr.toString());
      if (client == null) {
        Class<? extends NettyTransceiver> waspClientClass = NettyTransceiver.class;
  
        // Make an wasp rpc client.
        try {
          Constructor<? extends NettyTransceiver> cst = waspClientClass
              .getConstructor(InetSocketAddress.class, Long.class);
          client = cst.newInstance(addr, conf.getLong(
              FConstants.WASP_CONNECTION_TIMEOUT_MILLIS,
              FConstants.DEFAULT_CONNECTION_TIMEOUT_MILLIS));
          client.setConf(conf);
        } catch (InvocationTargetException e) {
          throw new RuntimeException(e);
        } catch (InstantiationException e) {
          throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
          throw new RuntimeException(e);
        } catch (NoSuchMethodException e) {
          throw new RuntimeException("No matching constructor in "
              + waspClientClass.getName(), e);
        }
  
        clients.put(addr.toString(), client);
      } else {
        client.incCount();
      }
      return client;
    }
  
    /**
     * Stop a RPC client connection A RPC client is closed only when its reference
     * count becomes zero.
     * 
     * @param client
     *          client to stop
     */
    protected void stopClient(NettyTransceiver client) {
      synchronized (this) {
        client.decCount();
        if (client.isZeroReference()) {
          clients.remove(client.getRemoteAddr().toString());
        }
      }
      if (client.isZeroReference()) {
        client.close();
      }
    }
  }