class KafkaRequestHandler(id: Int, brokerId: Int, val aggregateIdleMeter: Meter,
                          val totalHandlerThreads: Int, val requestChannel: RequestChannel,
                          apis: KafkaApis) extends Runnable with Logging {
  def run() {
    while(true) {
      try {
        var req : RequestChannel.Request = null
        while (req == null) {
          val startSelectTime = SystemTime.nanoseconds
          // 從requestChannel.requestQueue隊列里獲取請求
          req = requestChannel.receiveRequest(300)
          val idleTime = SystemTime.nanoseconds - startSelectTime
          aggregateIdleMeter.mark(idleTime / totalHandlerThreads)
        }
        apis.handle(req)
      } catch {
        case e: Throwable => error("Exception when handling request", e)
      }
    }
  }
}

// 在KafkaServer啟動會創建KafkaRequestHandlerPool
class KafkaRequestHandlerPool(val brokerId: Int, val requestChannel: RequestChannel,
                              val apis: KafkaApis,
                              numThreads: Int) extends Logging with KafkaMetricsGroup {
  // 線程池里的線程個數
  val threads = new Array[Thread](numThreads)
  // KafkaRequestHandler集合
  val runnables = new Array[KafkaRequestHandler](numThreads)
  // 創建并啟動KafkaRequestHandler線程
  for(i <- 0 until numThreads) {
    runnables(i) = new KafkaRequestHandler(i, brokerId, aggregateIdleMeter, numThreads, requestChannel, apis)
    threads(i) = Utils.daemonThread("kafka-request-handler-" + i, runnables(i))
    threads(i).start()
  }
}

class KafkaApis(val requestChannel: RequestChannel, val replicaManager: ReplicaManager,
                val coordinator: GroupCoordinator, val controller: KafkaController, val zkUtils: ZkUtils,
                val brokerId: Int, val config: KafkaConfig, val metadataCache: MetadataCache,
                val metrics: Metrics, val authorizer: Option[Authorizer]) extends Logging {

  def handle(request: RequestChannel.Request) {
    try {
      // 根據requestId分發請求
      ApiKeys.forId(request.requestId) match {
        case ApiKeys.PRODUCE => handleProducerRequest(request)
        case ApiKeys.FETCH => handleFetchRequest(request)
        case ApiKeys.LIST_OFFSETS => handleOffsetRequest(request)
        case ApiKeys.METADATA => handleTopicMetadataRequest(request)
        case ApiKeys.LEADER_AND_ISR => handleLeaderAndIsrRequest(request)
        case ApiKeys.STOP_REPLICA => handleStopReplicaRequest(request)
        case ApiKeys.UPDATE_METADATA_KEY => handleUpdateMetadataRequest(request)
        case ApiKeys.CONTROLLED_SHUTDOWN_KEY => handleControlledShutdownRequest(request)
        case ApiKeys.OFFSET_COMMIT => handleOffsetCommitRequest(request)
        case ApiKeys.OFFSET_FETCH => handleOffsetFetchRequest(request)
        case ApiKeys.GROUP_COORDINATOR => handleGroupCoordinatorRequest(request)
        case ApiKeys.JOIN_GROUP => handleJoinGroupRequest(request)
        case ApiKeys.HEARTBEAT => handleHeartbeatRequest(request)
        case ApiKeys.LEAVE_GROUP => handleLeaveGroupRequest(request)
        case ApiKeys.SYNC_GROUP => handleSyncGroupRequest(request)
        case ApiKeys.DESCRIBE_GROUPS => handleDescribeGroupRequest(request)
        case ApiKeys.LIST_GROUPS => handleListGroupsRequest(request)
        case ApiKeys.SASL_HANDSHAKE => handleSaslHandshakeRequest(request)
        case ApiKeys.API_VERSIONS => handleApiVersionsRequest(request)
        case requestId => throw new KafkaException("Unknown api code " + requestId)
      }
    } catch {
    } finally
      request.apiLocalCompleteTimeMs = SystemTime.milliseconds
  }
}