kafka 的network

好了 ， 接着上一章 ， 我们回到kafka的 kafkaserver 这个重量级的类。

 

      val handlers = new KafkaRequestHandlers(logManager)
    socketServer = new SocketServer(config.port,
                                    config.numThreads,
                                    config.monitoringPeriodSecs,
                                    handlers.handlerFor,
                                    config.socketSendBuffer,
                                    config.socketReceiveBuffer,                                    
                                    config.maxSocketRequestSize)

 在初始化zk连接， 加载topic信息之后。kafka开始跟做一些io的东西。个人对这部分还是很感兴趣的。让我们点进去看一看。 

注释写的很精彩啊：

/**
 * An NIO socket server. The thread model is
 *   1 Acceptor thread that handles new connections
 *   N Processor threads that each have their own selectors and handle all requests from their connections synchronously
 */

 他都已经说了，这是 NIO 线程模型是 单线程负责处理所以的连接。n个线程异步处理这些连接。

 

从这个注释入手，我们看一看 Acceptor 和 Processor 是如何实现的。

 

/**
 * Thread that accepts and configures new connections. There is only need for one of these
 */
private[kafka] class Acceptor(val port: Int, private val processors: Array[Processor], val sendBufferSize: Int, val receiveBufferSize: Int) extends AbstractServerThread {

  /**
   * Accept loop that checks for new connection attempts
   */
  def run() {
    val serverChannel = ServerSocketChannel.open()
    serverChannel.configureBlocking(false)
    serverChannel.socket.bind(new InetSocketAddress(port))
    serverChannel.register(selector, SelectionKey.OP_ACCEPT);
    logger.info("Awaiting connections on port " + port)
    startupComplete()

    var currentProcessor = 0
    while(isRunning) {
      val ready = selector.select(500)
      if(ready > 0) {
        val keys = selector.selectedKeys()
        val iter = keys.iterator()
        while(iter.hasNext && isRunning) {
          var key: SelectionKey = null
          try {
            key = iter.next
            iter.remove()

            if(key.isAcceptable)
                accept(key, processors(currentProcessor))
              else
                throw new IllegalStateException("Unrecognized key state for acceptor thread.")

              // round robin to the next processor thread
              currentProcessor = (currentProcessor + 1) % processors.length
          } catch {
            case e: Throwable => logger.error("Error in acceptor", e)
          }
        }
      }
    }
    logger.debug("Closing server socket and selector.")
    Utils.swallow(logger.error, serverChannel.close())
    Utils.swallow(logger.error, selector.close())
    shutdownComplete()
  }

 如果明白 java NIO 的相关部分，就会比较容易看懂这部分，忘了的上网搜搜。 一段标准的java server端的NIO 的操作， 绑定端口，注册事件，轮询 selector。如果有连接事件，就交给 processor 来处理。 简单而强有力的做法。下面看看Processor 是咋实现的。

 

 

  private val newConnections = new ConcurrentLinkedQueue[SocketChannel]();
  private val requestLogger = Logger.getLogger("kafka.request.logger")

  override def run() {
    startupComplete()
    while(isRunning) {
      // setup any new connections that have been queued up
      configureNewConnections()

      val ready = selector.select(500)
      if(ready > 0) {
        val keys = selector.selectedKeys()
        val iter = keys.iterator()
        while(iter.hasNext && isRunning) {
          var key: SelectionKey = null
          try {
            key = iter.next
            iter.remove()

            if(key.isReadable)
              read(key)
            else if(key.isWritable)
              write(key)
            else if(!key.isValid)
              close(key)
            else
              throw new IllegalStateException("Unrecognized key state for processor thread.")
          } catch {
            case e: EOFException => {
              logger.info("Closing socket connection to %s.".format(channelFor(key).socket.getInetAddress))
              close(key)
        }
        case e: InvalidRequestException => {
          logger.info("Closing socket connection to %s due to invalid request: %s".format(channelFor(key).socket.getInetAddress, e.getMessage))
          close(key)
            } case e: Throwable => {
              logger.error("Closing socket for " + channelFor(key).socket.getInetAddress + " because of error", e)
              close(key)
            }
          }
        }
      }
    }
    logger.debug("Closing selector.")
    Utils.swallow(logger.info, selector.close())
    shutdownComplete()
  }

 

 

好 ， 咱们看看首先他有一个newConnections队列 用来存储SocketChannel 对象，实际上可以看成缓存请求的消息队列。

在 run方法中， 先清空了这个队列，同时在selector 中注册这些事件。然后又是nio的一段标准的程序。看看read 方法中都干了什么：

  /**
   * Handle a completed request producing an optional response
   */
  private def handle(key: SelectionKey, request: Receive): Option[Send] = {
    val requestTypeId = request.buffer.getShort()
    if(requestLogger.isTraceEnabled) {
      requestTypeId match {
        case RequestKeys.Produce =>
          requestLogger.trace("Handling produce request from " + channelFor(key).socket.getRemoteSocketAddress())
        case RequestKeys.Fetch =>
          requestLogger.trace("Handling fetch request from " + channelFor(key).socket.getRemoteSocketAddress())
        case RequestKeys.MultiFetch =>
          requestLogger.trace("Handling multi-fetch request from " + channelFor(key).socket.getRemoteSocketAddress())
        case RequestKeys.MultiProduce =>
          requestLogger.trace("Handling multi-produce request from " + channelFor(key).socket.getRemoteSocketAddress())
        case RequestKeys.Offsets =>
          requestLogger.trace("Handling offset request from " + channelFor(key).socket.getRemoteSocketAddress())
        case _ => throw new InvalidRequestException("No mapping found for handler id " + requestTypeId)
      }
    }
    val handler = handlerMapping(requestTypeId, request)
    if(handler == null)
      throw new InvalidRequestException("No handler found for request")
    val start = time.nanoseconds
    val maybeSend = handler(request)
    stats.recordRequest(requestTypeId, time.nanoseconds - start)
    maybeSend
  }

 

 关键是匹配事件之后，他们都干了什么。由于对scala 语法不是那么纯熟，不知道咱们的就调用到了

        var  response: MessageSetSend = null
    try {
      trace("Fetching log segment for topic, partition, offset, maxSize = " + fetchRequest)
      val log = logManager.getLog(fetchRequest.topic, fetchRequest.partition)
      if (log != null) {
        response = new MessageSetSend(log.read(fetchRequest.offset, fetchRequest.maxSize))
        BrokerTopicStat.getBrokerTopicStat(fetchRequest.topic).recordBytesOut(response.messages.sizeInBytes)
        BrokerTopicStat.getBrokerAllTopicStat.recordBytesOut(response.messages.sizeInBytes)
      }
      else
        response = new MessageSetSend()
    }

 也就是说 在消费消息的时候是把 内容封装到 MessageSetSend 中作为参数返回给客户端。