kafka源码解析之七KafkaRequestHandlerPool

KafkaRequestHandlerPool的逻辑比较简单，就是开启num.io.threads个KafkaRequestHandler，每个KafkaRequestHandler从RequestChannel

. requestQueue 接受request，然后把对应的response存进responseQueues(i)队列

class KafkaRequestHandlerPool(val brokerId: Int,
                              val requestChannel: RequestChannel,
                              val apis: KafkaApis,
                              numThreads: Int) extends Logging with KafkaMetricsGroup {

  /* a meter to track the average free capacity of the request handlers */
  private val aggregateIdleMeter = newMeter("RequestHandlerAvgIdlePercent", "percent", TimeUnit.NANOSECONDS)

  this.logIdent = "[Kafka Request Handler on Broker " + brokerId + "], "
  val threads = new Array[Thread](numThreads)
  val runnables = new Array[KafkaRequestHandler](numThreads)
  for(i <- 0 until numThreads) {//创建num.io.threads个KafkaRequestHandler
    runnables(i) = new KafkaRequestHandler(i, brokerId, aggregateIdleMeter, numThreads, requestChannel, apis)
    threads(i) = Utils.daemonThread("kafka-request-handler-" + i, runnables(i))
    threads(i).start()
  }

  def shutdown() {
    info("shutting down")
    for(handler <- runnables)
      handler.shutdown
    for(thread <- threads)
      thread.join
    info("shut down completely")
  }
}

class KafkaRequestHandler(id: Int,
                          brokerId: Int,
                          val aggregateIdleMeter: Meter,
                          val totalHandlerThreads: Int,
                          val requestChannel: RequestChannel,
                          apis: KafkaApis) extends Runnable with Logging {
  this.logIdent = "[Kafka Request Handler " + id + " on Broker " + brokerId + "], "

  def run() {
    while(true) {
      try {
        var req : RequestChannel.Request = null
        while (req == null) {
          // We use a single meter for aggregate idle percentage for the thread pool.
          // Since meter is calculated as total_recorded_value / time_window and
          // time_window is independent of the number of threads, each recorded idle
          // time should be discounted by # threads.
          val startSelectTime = SystemTime.nanoseconds
          req = requestChannel.receiveRequest(300)//从RequestChannel.requestQueue获取request
          val idleTime = SystemTime.nanoseconds - startSelectTime
          aggregateIdleMeter.mark(idleTime / totalHandlerThreads)
        }
        if(req eq RequestChannel.AllDone) {
          debug("Kafka request handler %d on broker %d received shut down command".format(
            id, brokerId))
          return
        }
        req.requestDequeueTimeMs = SystemTime.milliseconds
        trace("Kafka request handler %d on broker %d handling request %s".format(id, brokerId, req))
        apis.handle(req)//调用负责业务逻辑的KafkaApis进行真正的处理，然后把response存放进对应的RequestChannel. responseQueues[i]
      } catch {
        case e: Throwable => error("Exception when handling request", e)
      }
    }
  }
  def shutdown(): Unit = requestChannel.sendRequest(RequestChannel.AllDone)
}