Package eu.stratosphere.nephele.ipc

Source Code of eu.stratosphere.nephele.ipc.Server$Handler

/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* 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
*
*     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.
**********************************************************************************************************************/

/**
* This file is based on source code from the Hadoop Project (http://hadoop.apache.org/), licensed by the Apache
* Software Foundation (ASF) under the Apache License, Version 2.0. See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/

package eu.stratosphere.nephele.ipc;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.net.BindException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.WritableByteChannel;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import eu.stratosphere.core.io.IOReadableWritable;
import eu.stratosphere.core.io.StringRecord;
import eu.stratosphere.core.protocols.VersionedProtocol;
import eu.stratosphere.util.ClassUtils;

/**
* An abstract IPC service. IPC calls take a single {@link Writable} as a
* parameter, and return a {@link Writable} as their value. A service runs on
* a port and is defined by a parameter class and a value class.
*
* @see Client
*/
public abstract class Server {

  public static final Log LOG = LogFactory.getLog(Server.class);

  private static final Class<?>[] EMPTY_ARRAY = new Class[] {};

  public static final ByteBuffer HEADER = ByteBuffer.wrap("crpc".getBytes());

  /**
   * How many calls/handler are allowed in the queue.
   */
  private static final int MAX_QUEUE_SIZE_PER_HANDLER = 100;

  private static final ThreadLocal<Server> SERVER = new ThreadLocal<Server>();

  private static final Map<String, Class<? extends VersionedProtocol>> PROTOCOL_CACHE = new ConcurrentHashMap<String, Class<? extends VersionedProtocol>>();

  static Class<? extends VersionedProtocol> getProtocolClass(String protocolName) throws ClassNotFoundException {

    Class<? extends VersionedProtocol> protocol = PROTOCOL_CACHE.get(protocolName);
    if (protocol == null) {
      protocol = (Class<? extends VersionedProtocol>) ClassUtils.getProtocolByName(protocolName);
      PROTOCOL_CACHE.put(protocolName, protocol);
    }
    return protocol;
  }

  /**
   * Returns the server instance called under or null. May be called under {@link #call(Writable, long)}
   * implementations, and under {@link Writable} methods of paramters and return values. Permits applications to
   * access
   * the server context.
   */
  public static Server get() {
    return SERVER.get();
  }

  /**
   * This is set to Call object before Handler invokes an RPC and reset
   * after the call returns.
   */
  private static final ThreadLocal<Call> CurCall = new ThreadLocal<Call>();

  /**
   * Returns the remote side ip address when invoked inside an RPC
   * Returns null incase of an error.
   */
  public static InetAddress getRemoteIp() {
    Call call = CurCall.get();
    if (call != null) {
      return call.connection.socket.getInetAddress();
    }
    return null;
  }

  /**
   * Returns remote address as a string when invoked inside an RPC.
   * Returns null in case of an error.
   */
  public static String getRemoteAddress() {
    InetAddress addr = getRemoteIp();
    return (addr == null) ? null : addr.getHostAddress();
  }

  private String bindAddress;

  private int port; // port we listen on

  private int handlerCount; // number of handler threads

  private Class<? extends IOReadableWritable> invocationClass; // invocation class to call

  private int maxIdleTime; // the maximum idle time after

  // which a client may be disconnected
  private int thresholdIdleConnections; // the number of idle connections

  // after which we will start
  // cleaning up idle
  // connections
  int maxConnectionsToNuke; // the max number of

  // connections to nuke
  // during a cleanup

  private int maxQueueSize;

  private int socketSendBufferSize;

  private final boolean tcpNoDelay; // if T then disable Nagle's Algorithm

  volatile private boolean running = true; // true while server runs

  private BlockingQueue<Call> callQueue; // queued calls

  private List<Connection> connectionList = Collections.synchronizedList(new LinkedList<Connection>());

  // maintain a list
  // of client connections
  private Listener listener = null;

  private Responder responder = null;

  private int numConnections = 0;

  private Handler[] handlers = null;

  /**
   * A convenience method to bind to a given address and report
   * better exceptions if the address is not a valid host.
   *
   * @param socket
   *        the socket to bind
   * @param address
   *        the address to bind to
   * @param backlog
   *        the number of connections allowed in the queue
   * @throws BindException
   *         if the address can't be bound
   * @throws UnknownHostException
   *         if the address isn't a valid host name
   * @throws IOException
   *         other random errors from bind
   */
  public static void bind(ServerSocket socket, InetSocketAddress address, int backlog) throws IOException {
    try {
      socket.bind(address, backlog);
    } catch (BindException e) {
      BindException bindException = new BindException("Problem binding to " + address + " : " + e.getMessage());
      bindException.initCause(e);
      throw bindException;
    } catch (SocketException e) {
      // If they try to bind to a different host's address, give a better
      // error message.
      if ("Unresolved address".equals(e.getMessage())) {
        throw new UnknownHostException("Invalid hostname for server: " + address.getHostName());
      } else {
        throw e;
      }
    }
  }

  /** A call queued for handling. */
  private static class Call {
    private int id; // the client's call id

    private IOReadableWritable param; // the parameter passed

    private Connection connection; // connection to client

    private long timestamp; // the time received when response is null

    // the time served when response is not null
    private ByteBuffer response; // the response for this call

    public Call(int id, IOReadableWritable param, Connection connection) {
      this.id = id;
      this.param = param;
      this.connection = connection;
      this.timestamp = System.currentTimeMillis();
      this.response = null;
    }

    @Override
    public String toString() {
      return param.toString() + " from " + connection.toString();
    }

    public void setResponse(ByteBuffer response) {
      this.response = response;
    }
  }

  /** Listens on the socket. Creates jobs for the handler threads */
  private class Listener extends Thread {

    private ServerSocketChannel acceptChannel = null; // the accept channel

    private Selector selector = null; // the selector that we use for the server

    private InetSocketAddress address; // the address we bind at

    private Random rand = new Random();

    private long lastCleanupRunTime = 0; // the last time when a cleanup connec-

    // -tion (for idle connections) ran
    private long cleanupInterval = 10000; // the minimum interval between

    // two cleanup runs
    private int backlogLength = 128;

    private volatile boolean shutDown = false;

    public Listener()
              throws IOException {
      address = new InetSocketAddress(bindAddress, port);
      // Create a new server socket and set to non blocking mode
      acceptChannel = ServerSocketChannel.open();
      acceptChannel.configureBlocking(false);

      // Bind the server socket to the local host and port
      bind(acceptChannel.socket(), address, backlogLength);
      port = acceptChannel.socket().getLocalPort(); // Could be an ephemeral port
      // create a selector;
      selector = Selector.open();

      // Register accepts on the server socket with the selector.
      acceptChannel.register(selector, SelectionKey.OP_ACCEPT);
      this.setName("IPC Server listener on " + port);
      this.setDaemon(true);
    }

    /**
     * cleanup connections from connectionList. Choose a random range
     * to scan and also have a limit on the number of the connections
     * that will be cleanedup per run. The criteria for cleanup is the time
     * for which the connection was idle. If 'force' is true then all
     * connections will be looked at for the cleanup.
     */
    private void cleanupConnections(boolean force) {
      if (force || numConnections > thresholdIdleConnections) {
        long currentTime = System.currentTimeMillis();
        if (!force && (currentTime - lastCleanupRunTime) < cleanupInterval) {
          return;
        }
        int start = 0;
        int end = numConnections - 1;
        if (!force) {
          start = rand.nextInt() % numConnections;
          end = rand.nextInt() % numConnections;
          int temp;
          if (end < start) {
            temp = start;
            start = end;
            end = temp;
          }
        }
        int i = start;
        int numNuked = 0;
        while (i <= end) {
          Connection c;
          synchronized (connectionList) {
            try {
              c = connectionList.get(i);
            } catch (Exception e) {
              return;
            }
          }
          if (c.timedOut(currentTime)) {
           
            closeConnection(c);
            numNuked++;
            end--;
            c = null;
            if (!force && numNuked == maxConnectionsToNuke) {
              break;
            }
          } else {
            i++;
          }
        }
        lastCleanupRunTime = System.currentTimeMillis();
      }
    }

    @Override
    public void run() {
      LOG.debug(getName() + ": starting");
      SERVER.set(Server.this);
      while (running) {
        SelectionKey key = null;
        try {
          selector.select();
          Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
          while (iter.hasNext()) {
            key = iter.next();
            iter.remove();
            try {
              if (key.isValid()) {
                if (key.isAcceptable()) {
                  doAccept(key);
                } else if (key.isReadable()) {
                  doRead(key);
                }
              }
            } catch (IOException e) {
            }
            key = null;
          }
        } catch (OutOfMemoryError e) {
          // we can run out of memory if we have too many threads
          // log the event and sleep for a minute and give
          // some thread(s) a chance to finish
          LOG.warn("Out of Memory in server select", e);
          closeCurrentConnection(key, e);
          cleanupConnections(true);
          try {
            Thread.sleep(60000);
          } catch (Exception ie) {
          }
        } catch (InterruptedException e) {
          if (running) { // unexpected -- log it
            LOG.info(getName() + " caught: " + e.toString());
          }
        } catch (Exception e) {
          closeCurrentConnection(key, e);
        }
        cleanupConnections(false);
      }
      LOG.debug("Stopping " + this.getName());

      synchronized (this) {
        try {
          acceptChannel.close();
          selector.close();
        } catch (IOException e) {
        }

        selector = null;
        acceptChannel = null;

        // clean up all connections
        while (!connectionList.isEmpty()) {
          closeConnection(connectionList.remove(0));
        }
      }

      this.shutDown = true;
    }

    public boolean isShutDown() {
      return this.shutDown;
    }

    private void closeCurrentConnection(SelectionKey key, Throwable e) {
      if (key != null) {
        Connection c = (Connection) key.attachment();
        if (c != null) {
          closeConnection(c);
          c = null;
        }
      }
    }

    InetSocketAddress getAddress() {
      return (InetSocketAddress) acceptChannel.socket().getLocalSocketAddress();
    }

    void doAccept(SelectionKey key) throws IOException, OutOfMemoryError {
      Connection c = null;
      ServerSocketChannel server = (ServerSocketChannel) key.channel();
      // accept up to 10 connections
      for (int i = 0; i < 10; i++) {
        SocketChannel channel = server.accept();
        if (channel == null) {
          return;
        }

        channel.configureBlocking(false);
        channel.socket().setTcpNoDelay(tcpNoDelay);
        SelectionKey readKey = channel.register(selector, SelectionKey.OP_READ);
        c = new Connection(readKey, channel, System.currentTimeMillis());
        readKey.attach(c);
        synchronized (connectionList) {
          connectionList.add(numConnections, c);
          numConnections++;
        }
      }
    }

    void doRead(SelectionKey key) throws InterruptedException {
      int count = 0;
      Connection c = (Connection) key.attachment();
      if (c == null) {
        return;
      }
      c.setLastContact(System.currentTimeMillis());

      try {
        count = c.readAndProcess();
      } catch (InterruptedException ieo) {
        LOG.info(getName() + ": readAndProcess caught InterruptedException", ieo);
        throw ieo;
      } catch (Exception e) {
        LOG.info(getName() + ": readAndProcess threw exception " + e + ". Count of bytes read: " + count, e);
        count = -1; // so that the (count < 0) block is executed
      }
      if (count < 0) {
        closeConnection(c);
        c = null;
      } else {
        c.setLastContact(System.currentTimeMillis());
      }
    }

    synchronized void doStop() {
      if (selector != null) {
        selector.wakeup();
        Thread.yield();
      }
      if (acceptChannel != null) {
        try {
          acceptChannel.socket().close();
        } catch (IOException e) {
          LOG.info(getName() + ":Exception in closing listener socket. " + e);
        }
      }
    }
  }

  // Sends responses of RPC back to clients.
  private class Responder extends Thread {
    private Selector writeSelector;

    private int pending; // connections waiting to register

    final static int PURGE_INTERVAL = 900000; // 15mins

    private volatile boolean shutDown = false;

    Responder()
          throws IOException {
      this.setName("IPC Server Responder");
      this.setDaemon(true);
      writeSelector = Selector.open(); // create a selector
      pending = 0;
    }

    @Override
    public void run() {
      LOG.debug(getName() + ": starting");
      SERVER.set(Server.this);
      long lastPurgeTime = 0; // last check for old calls.

      while (running) {
        try {
          waitPending(); // If a channel is being registered, wait.
          writeSelector.select(PURGE_INTERVAL);
          Iterator<SelectionKey> iter = writeSelector.selectedKeys().iterator();
          while (iter.hasNext()) {
            SelectionKey key = iter.next();
            iter.remove();
            try {
              if (key.isValid() && key.isWritable()) {
                doAsyncWrite(key);
              }
            } catch (IOException e) {
              LOG.info(getName() + ": doAsyncWrite threw exception " + e);
            }
          }
          long now = System.currentTimeMillis();
          if (now < lastPurgeTime + PURGE_INTERVAL) {
            continue;
          }
          lastPurgeTime = now;
          //
          // If there were some calls that have not been sent out for a
          // long time, discard them.
          //
          ArrayList<Call> calls;

          // get the list of channels from list of keys.
          synchronized (writeSelector.keys()) {
            calls = new ArrayList<Call>(writeSelector.keys().size());
            iter = writeSelector.keys().iterator();
            while (iter.hasNext()) {
              SelectionKey key = iter.next();
              Call call = (Call) key.attachment();
              if (call != null && key.channel() == call.connection.channel) {
                calls.add(call);
              }
            }
          }

          for (Call call : calls) {
            try {
              doPurge(call, now);
            } catch (IOException e) {
              LOG.warn("Error in purging old calls " + e);
            }
          }
        } catch (OutOfMemoryError e) {
          //
          // we can run out of memory if we have too many threads
          // log the event and sleep for a minute and give
          // some thread(s) a chance to finish
          //
          LOG.warn("Out of Memory in server select", e);
          try {
            Thread.sleep(60000);
          } catch (Exception ie) {
          }
        } catch (Exception e) {
          LOG.warn("Exception in Responder " + e.toString());
        }
      }
      LOG.debug("Stopping " + this.getName());

      this.shutDown = true;
    }

    public boolean isShutDown() {
      return this.shutDown;
    }

    private void doAsyncWrite(SelectionKey key) throws IOException {
      Call call = (Call) key.attachment();
      if (call == null) {
        return;
      }
      if (key.channel() != call.connection.channel) {
        throw new IOException("doAsyncWrite: bad channel");
      }

      synchronized (call.connection.responseQueue) {
        if (processResponse(call.connection.responseQueue, false)) {
          try {
            key.interestOps(0);
          } catch (CancelledKeyException e) {
            /*
             * The Listener/reader might have closed the socket.
             * We don't explicitly cancel the key, so not sure if this will
             * ever fire.
             * This warning could be removed.
             */
            LOG.warn("Exception while changing ops : " + e);
          }
        }
      }
    }

    //
    // Remove calls that have been pending in the responseQueue
    // for a long time.
    //
    private void doPurge(Call call, long now) throws IOException {
      LinkedList<Call> responseQueue = call.connection.responseQueue;
      synchronized (responseQueue) {
        Iterator<Call> iter = responseQueue.listIterator(0);
        while (iter.hasNext()) {
          call = iter.next();
          if (now > call.timestamp + PURGE_INTERVAL) {
            closeConnection(call.connection);
            break;
          }
        }
      }
    }

    // Processes one response. Returns true if there are no more pending
    // data for this channel.
    //
    private boolean processResponse(LinkedList<Call> responseQueue, boolean inHandler) throws IOException {
      boolean error = true;
      boolean done = false; // there is more data for this channel.
      int numElements = 0;
      Call call = null;
      try {
        synchronized (responseQueue) {
          //
          // If there are no items for this channel, then we are done
          //
          numElements = responseQueue.size();
          if (numElements == 0) {
            error = false;
            return true; // no more data for this channel.
          }
          //
          // Extract the first call
          //
          call = responseQueue.removeFirst();
          SocketChannel channel = call.connection.channel;
         
          //
          // Send as much data as we can in the non-blocking fashion
          //
          int numBytes = channelWrite(channel, call.response);
          if (numBytes < 0) {
            return true;
          }
          if (!call.response.hasRemaining()) {
            call.connection.decRpcCount();
            if (numElements == 1) { // last call fully processes.
              done = true; // no more data for this channel.
            } else {
              done = false; // more calls pending to be sent.
            }
          } else {
            //
            // If we were unable to write the entire response out, then
            // insert in Selector queue.
            //
            call.connection.responseQueue.addFirst(call);

            if (inHandler) {
              // set the serve time when the response has to be sent later
              call.timestamp = System.currentTimeMillis();

              incPending();
              try {
                // Wakeup the thread blocked on select, only then can the call
                // to channel.register() complete.
                writeSelector.wakeup();
                channel.register(writeSelector, SelectionKey.OP_WRITE, call);
              } catch (ClosedChannelException e) {
                // Its ok. channel might be closed else where.
                done = true;
              } finally {
                decPending();
              }
            }
          }
          error = false; // everything went off well
        }
      } finally {
        if (error && call != null) {
          LOG.warn(getName() + ", call " + call + ": output error");
          done = true; // error. no more data for this channel.
          closeConnection(call.connection);
        }
      }
      return done;
    }

    //
    // Enqueue a response from the application.
    //
    void doRespond(Call call) throws IOException {
      synchronized (call.connection.responseQueue) {
        call.connection.responseQueue.addLast(call);
        if (call.connection.responseQueue.size() == 1) {
          processResponse(call.connection.responseQueue, true);
        }
      }
    }

    private synchronized void incPending() { // call waiting to be enqueued.
      pending++;
    }

    private synchronized void decPending() { // call done enqueueing.
      pending--;
      notify();
    }

    private synchronized void waitPending() throws InterruptedException {
      while (pending > 0) {
        wait();
      }
    }
  }

  /** Reads calls from a connection and queues them for handling. */
  private class Connection {
    private boolean headerRead = false; // if the connection header that

    // follows version is read.
    private boolean protocolRead = false;

    private SocketChannel channel;

    private ByteBuffer data;

    private ByteBuffer dataLengthBuffer;

    private LinkedList<Call> responseQueue;

    private volatile int rpcCount = 0; // number of outstanding rpcs

    private long lastContact;

    private int dataLength;

    private Socket socket;

    // Cache the remote host & port info so that even if the socket is
    // disconnected, we can say where it used to connect to.
    private String hostAddress;

    private int remotePort;

    ConnectionHeader header = new ConnectionHeader();

    Class<? extends VersionedProtocol> protocol;

    public Connection(SelectionKey key, SocketChannel channel, long lastContact) {
      this.channel = channel;
      this.lastContact = lastContact;
      this.data = null;
      this.dataLengthBuffer = ByteBuffer.allocate(4);
      this.socket = channel.socket();
      InetAddress addr = socket.getInetAddress();
      if (addr == null) {
        this.hostAddress = "*Unknown*";
      } else {
        this.hostAddress = addr.getHostAddress();
      }
      this.remotePort = socket.getPort();
      this.responseQueue = new LinkedList<Call>();
      if (socketSendBufferSize != 0) {
        try {
          socket.setSendBufferSize(socketSendBufferSize);
        } catch (IOException e) {
          LOG.warn("Connection: unable to set socket send buffer size to " + socketSendBufferSize);
        }
      }
    }

    @Override
    public String toString() {
      return getHostAddress() + ":" + remotePort;
    }

    public String getHostAddress() {
      return hostAddress;
    }

    public void setLastContact(long lastContact) {
      this.lastContact = lastContact;
    }

    /* Return true if the connection has no outstanding rpc */
    private boolean isIdle() {
      return rpcCount == 0;
    }

    /* Decrement the outstanding RPC count */
    private void decRpcCount() {
      rpcCount--;
    }

    /* Increment the outstanding RPC count */
    private void incRpcCount() {
      rpcCount++;
    }

    private boolean timedOut(long currentTime) {
      if (isIdle() && currentTime - lastContact > maxIdleTime) {
        return true;
      }
      return false;
    }

    public int readAndProcess() throws IOException, InterruptedException {
      while (true) {
        /*
         * Read at most one RPC. If the header is not read completely yet
         * then iterate until we read first RPC or until there is no data left.
         */
        int count = -1;
        if (dataLengthBuffer.remaining() > 0) {
          count = channelRead(channel, dataLengthBuffer);
          if (count < 0 || dataLengthBuffer.remaining() > 0) {
            return count;
          }
        }

        if (!headerRead) {
          dataLengthBuffer.flip();
          if (!HEADER.equals(dataLengthBuffer)) {
            // Warning is ok since this is not supposed to happen.
            LOG.warn("Incorrect header from " + hostAddress + ":" + remotePort);
            return -1;
          }
          dataLengthBuffer.clear();
          headerRead = true;
          continue;
        }

        if (data == null) {
          dataLengthBuffer.flip();
          dataLength = dataLengthBuffer.getInt();

          if (dataLength == Client.PING_CALL_ID) {
            dataLengthBuffer.clear();
            return 0; // ping message
          }
          data = ByteBuffer.allocate(dataLength);
          incRpcCount(); // Increment the rpc count
        }

        count = channelRead(channel, data);

        if (data.remaining() == 0) {
          dataLengthBuffer.clear();
          data.flip();
          if (protocolRead) {
            processData();
            data = null;
            return count;
          } else {
            processProtocol();
            protocolRead = true;
            data = null;

            // Authorizitation is intenionally left out

            continue;
          }
        }
        return count;
      }
    }

    // / Reads the connection header following version
    private void processProtocol() throws IOException {
      DataInputStream in = new DataInputStream(new ByteArrayInputStream(data.array()));
      header.read(in);
      try {
        String protocolClassName = header.getProtocol();
        if (protocolClassName != null) {
          protocol = getProtocolClass(header.getProtocol());
        }
      } catch (ClassNotFoundException cnfe) {
        LOG.error(cnfe);
        throw new IOException("Unknown protocol: " + header.getProtocol());
      }

    }

    private void processData() throws IOException, InterruptedException {
      DataInputStream dis = new DataInputStream(new ByteArrayInputStream(data.array()));
      int id = dis.readInt(); // try to read an id


      IOReadableWritable invocation = newInstance(invocationClass); // read param
      invocation.read(dis);

      Call call = new Call(id, invocation, this);
      callQueue.put(call); // queue the call; maybe blocked here
    }

    private synchronized void close() throws IOException {
      data = null;
      dataLengthBuffer = null;
      if (!channel.isOpen()) {
        return;
      }
      try {
        socket.shutdownOutput();
      } catch (Exception e) {
      }
      if (channel.isOpen()) {
        try {
          channel.close();
        } catch (Exception e) {
        }
      }
      try {
        socket.close();
      } catch (Exception e) {
      }
    }
  }

  /** Handles queued calls . */
  private class Handler extends Thread {

    private volatile boolean shutDown = false;

    public Handler(int instanceNumber) {
      this.setDaemon(true);
      this.setName("IPC Server handler " + instanceNumber + " on " + port);
    }

    @Override
    public void run() {
      LOG.debug(getName() + ": starting");
      SERVER.set(Server.this);
      ByteArrayOutputStream buf = new ByteArrayOutputStream(10240);
      while (running) {
        try {
          final Call call = callQueue.take(); // pop the queue; maybe blocked here

          String errorClass = null;
          String error = null;
          IOReadableWritable value = null;

          CurCall.set(call);

          value = call(call.connection.protocol, call.param, call.timestamp);

          CurCall.set(null);

          setupResponse(buf, call, (error == null) ? Status.SUCCESS : Status.ERROR, value, errorClass, error);
          responder.doRespond(call);
        } catch (InterruptedException e) {
          if (running) { // unexpected -- log it
            LOG.error(getName() + " caught: ", e);
          }
        } catch (Exception e) {
          LOG.error(getName() + " caught: ", e);
        }
      }
      LOG.debug(getName() + ": exiting");

      this.shutDown = true;
    }

    public boolean isShutDown() {

      return this.shutDown;
    }
  }

  protected Server(String bindAddress, int port, Class<? extends IOReadableWritable> paramClass, int handlerCount)
                                                          throws IOException {
    this(bindAddress, port, paramClass, handlerCount, Integer.toString(port));
  }

  /**
   * Constructs a server listening on the named port and address. Parameters passed must
   * be of the named class. The <code>handlerCount</handlerCount> determines
   * the number of handler threads that will be used to process calls.
   */
  protected Server(String bindAddress, int port, Class<? extends IOReadableWritable> invocationClass,
      int handlerCount, String serverName)
                        throws IOException {
    this.bindAddress = bindAddress;
    this.port = port;
    this.invocationClass = invocationClass;
    this.handlerCount = handlerCount;
    this.socketSendBufferSize = 0;
    this.maxQueueSize = handlerCount * MAX_QUEUE_SIZE_PER_HANDLER;
    this.callQueue = new LinkedBlockingQueue<Call>(maxQueueSize);
    this.maxIdleTime = 2 * 1000;
    this.maxConnectionsToNuke = 10;
    this.thresholdIdleConnections = 4000;

    // Start the listener here and let it bind to the port
    listener = new Listener();
    this.port = listener.getAddress().getPort();
    this.tcpNoDelay = false;

    // Create the responder here
    responder = new Responder();
  }

  private void closeConnection(Connection connection) {
    synchronized (connectionList) {
      if (connectionList.remove(connection)) {
        numConnections--;
      }
    }
    try {
      connection.close();
    } catch (IOException e) {
    }
  }

  /**
   * Setup response for the IPC Call.
   *
   * @param response
   *        buffer to serialize the response into
   * @param call
   *        {@link Call} to which we are setting up the response
   * @param status
   *        {@link Status} of the IPC call
   * @param rv
   *        return value for the IPC Call, if the call was successful
   * @param errorClass
   *        error class, if the the call failed
   * @param error
   *        error message, if the call failed
   * @throws IOException
   */
  private void setupResponse(ByteArrayOutputStream response, Call call, Status status, IOReadableWritable rv,
      String errorClass, String error) throws IOException {
    response.reset();
    DataOutputStream out = new DataOutputStream(response);
    out.writeInt(call.id); // write call id
    out.writeInt(status.state); // write status

    if (status == Status.SUCCESS) {
      if (rv == null) {
        out.writeBoolean(false);
      } else {
        out.writeBoolean(true);
        StringRecord.writeString(out, rv.getClass().getName());
        rv.write(out);
      }

    } else {
      StringRecord.writeString(out, errorClass);
      StringRecord.writeString(out, error);
    }
    call.setResponse(ByteBuffer.wrap(response.toByteArray()));
  }

  /** Sets the socket buffer size used for responding to RPCs */
  public void setSocketSendBufSize(int size) {
    this.socketSendBufferSize = size;
  }

  /** Starts the service. Must be called before any calls will be handled. */
  public synchronized void start() throws IOException {
    responder.start();
    listener.start();
    handlers = new Handler[handlerCount];

    for (int i = 0; i < handlerCount; i++) {
      handlers[i] = new Handler(i);
      handlers[i].start();
    }
  }

  /** Stops the service. No new calls will be handled after this is called. */
  public synchronized void stop() {
    LOG.debug("Stopping server on " + port);
    running = false;
    if (handlers != null) {
      for (int i = 0; i < handlerCount; i++) {
        if (handlers[i] != null) {
          handlers[i].interrupt();
        }
      }
    }
    listener.interrupt();
    listener.doStop();
    responder.interrupt();
    notifyAll();

    // Wait until shut down of handlers is complete
    if (this.handlers != null) {

      while (true) {

        int i = 0;
        for (; i < this.handlerCount; i++) {
          if (this.handlers[i] != null) {
            if (!this.handlers[i].isShutDown()) {
              break;
            }
          }
        }

        if (i < this.handlerCount) {
          try {
            wait(100);
          } catch (InterruptedException e) {
            break;
          }
        } else {
          // exit while loop
          break;
        }
      }
    }

    // Wait until shut down of responder is complete
    while (!this.responder.isShutDown()) {
      try {
        wait(100);
      } catch (InterruptedException e) {
        break;
      }
    }

    // Wait until shut down of listener is complete
    while (!this.listener.isShutDown()) {
      try {
        wait(100);
      } catch (InterruptedException e) {
        break;
      }
    }
  }

  /**
   * Wait for the server to be stopped.
   * Does not wait for all subthreads to finish.
   * See {@link #stop()}.
   */
  public synchronized void join() throws InterruptedException {
    while (running) {
      wait();
    }
  }

  /**
   * Return the socket (ip+port) on which the RPC server is listening to.
   *
   * @return the socket (ip+port) on which the RPC server is listening to.
   */
  public synchronized InetSocketAddress getListenerAddress() {
    return listener.getAddress();
  }

  /** Called for each call. */
  public abstract IOReadableWritable call(Class<?> protocol, IOReadableWritable param, long receiveTime)
      throws IOException;

  /**
   * The number of open RPC conections
   *
   * @return the number of open rpc connections
   */
  public int getNumOpenConnections() {
    return numConnections;
  }

  /**
   * The number of rpc calls in the queue.
   *
   * @return The number of rpc calls in the queue.
   */
  public int getCallQueueLen() {
    return callQueue.size();
  }

  /**
   * When the read or write buffer size is larger than this limit, i/o will be
   * done in chunks of this size. Most RPC requests and responses would be
   * be smaller.
   */
  private static int NIO_BUFFER_LIMIT = 8 * 1024; // should not be more than 64KB.

  /**
   * This is a wrapper around {@link WritableByteChannel#write(ByteBuffer)}.
   * If the amount of data is large, it writes to channel in smaller chunks.
   * This is to avoid jdk from creating many direct buffers as the size of
   * buffer increases. This also minimizes extra copies in NIO layer
   * as a result of multiple write operations required to write a large
   * buffer.
   *
   * @see WritableByteChannel#write(ByteBuffer)
   */
  private static int channelWrite(WritableByteChannel channel, ByteBuffer buffer) throws IOException {

    return (buffer.remaining() <= NIO_BUFFER_LIMIT) ? channel.write(buffer) : channelIO(null, channel, buffer);
  }

  /**
   * This is a wrapper around {@link ReadableByteChannel#read(ByteBuffer)}.
   * If the amount of data is large, it writes to channel in smaller chunks.
   * This is to avoid jdk from creating many direct buffers as the size of
   * ByteBuffer increases. There should not be any performance degredation.
   *
   * @see ReadableByteChannel#read(ByteBuffer)
   */
  private static int channelRead(ReadableByteChannel channel, ByteBuffer buffer) throws IOException {

    return (buffer.remaining() <= NIO_BUFFER_LIMIT) ? channel.read(buffer) : channelIO(channel, null, buffer);
  }

  /**
   * Helper for {@link #channelRead(ReadableByteChannel, ByteBuffer)} and
   * {@link #channelWrite(WritableByteChannel, ByteBuffer)}. Only
   * one of readCh or writeCh should be non-null.
   *
   * @see #channelRead(ReadableByteChannel, ByteBuffer)
   * @see #channelWrite(WritableByteChannel, ByteBuffer)
   */
  private static int channelIO(ReadableByteChannel readCh, WritableByteChannel writeCh, ByteBuffer buf)
      throws IOException {

    int originalLimit = buf.limit();
    int initialRemaining = buf.remaining();
    int ret = 0;

    while (buf.remaining() > 0) {
      try {
        int ioSize = Math.min(buf.remaining(), NIO_BUFFER_LIMIT);
        buf.limit(buf.position() + ioSize);

        ret = (readCh == null) ? writeCh.write(buf) : readCh.read(buf);

        if (ret < ioSize) {
          break;
        }

      } finally {
        buf.limit(originalLimit);
      }
    }

    int nBytes = initialRemaining - buf.remaining();
    return (nBytes > 0) ? nBytes : ret;
  }

  public static <T> T newInstance(Class<T> theClass) {
    T result;
    Constructor<T> meth = null;
    try {
      meth = theClass.getDeclaredConstructor(EMPTY_ARRAY);
      meth.setAccessible(true);
      result = meth.newInstance();
    } catch (Exception e) {
      throw new RuntimeException(e);
    }

    return result;
  }
}
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