KafkaController机制（十三）：ControlledShutdownRequest

KafkaController.shutdownBroker()方法时ControlledShutdownRequest的核心，使用ControlledShutdownLeaderSelector重新选择Leader副本和ISR集合，实现Leader副本的迁移。
 

  def shutdownBroker(id: Int) : Set[TopicAndPartition] = {

    if (!isActive()) {
      throw new ControllerMovedException("Controller moved to another broker. Aborting controlled shutdown")
    }

    controllerContext.brokerShutdownLock synchronized {
      info("Shutting down broker " + id)

      inLock(controllerContext.controllerLock) {
        if (!controllerContext.liveOrShuttingDownBrokerIds.contains(id))
          throw new BrokerNotAvailableException("Broker id %d does not exist.".format(id))

        controllerContext.shuttingDownBrokerIds.add(id)
        debug("All shutting down brokers: " + controllerContext.shuttingDownBrokerIds.mkString(","))
        debug("Live brokers: " + controllerContext.liveBrokerIds.mkString(","))
      }
      //获得待关闭的Broker上的所有Partition和副本信息
      val allPartitionsAndReplicationFactorOnBroker: Set[(TopicAndPartition, Int)] =
        inLock(controllerContext.controllerLock) {
          controllerContext.partitionsOnBroker(id)
            .map(topicAndPartition => (topicAndPartition, controllerContext.partitionReplicaAssignment(topicAndPartition).size))
        }

      allPartitionsAndReplicationFactorOnBroker.foreach {
        case(topicAndPartition, replicationFactor) =>
          // Move leadership serially to relinquish lock.
          inLock(controllerContext.controllerLock) {
            controllerContext.partitionLeadershipInfo.get(topicAndPartition).foreach { currLeaderIsrAndControllerEpoch =>
              if (replicationFactor > 1) {//副本数是否大于1
                //检测Leaader副本是否处于待关闭的Broker上
                if (currLeaderIsrAndControllerEpoch.leaderAndIsr.leader == id) {
                  // If the broker leads the topic partition, transition the leader and update isr. Updates zk and
                  // notifies all affected brokers
                  // 将相关的Partition切换为OnlinePartition状态，重新选择ISR和leader集合，把结果写入zk中，然后发送LeaderAndISRRequest和UpdateMeatadataRequest
                  partitionStateMachine.handleStateChanges(Set(topicAndPartition), OnlinePartition,
                    controlledShutdownPartitionLeaderSelector)
                } else {
                  // Stop the replica first. The state change below initiates ZK changes which should take some time
                  // before which the stop replica request should be completed (in most cases)
                  try {//发送StopReplicaRequest请求
                    brokerRequestBatch.newBatch()
                    brokerRequestBatch.addStopReplicaRequestForBrokers(Seq(id), topicAndPartition.topic,
                      topicAndPartition.partition, deletePartition = false)
                    brokerRequestBatch.sendRequestsToBrokers(epoch)
                  } catch {
                    case e : IllegalStateException => {
                      // Resign if the controller is in an illegal state
                      error("Forcing the controller to resign")
                      brokerRequestBatch.clear()
                      controllerElector.resign()

                      throw e
                    }
                  }
                  // If the broker is a follower, updates the isr in ZK and notifies the current leader
                  // 将副本转换为Offline状态
                  replicaStateMachine.handleStateChanges(Set(PartitionAndReplica(topicAndPartition.topic,
                    topicAndPartition.partition, id)), OfflineReplica)
                }
              }
            }
          }
      }
      //统计leader副本依然处于关闭Broker上的分区，并返回
      def replicatedPartitionsBrokerLeads() = inLock(controllerContext.controllerLock) {
        trace("All leaders = " + controllerContext.partitionLeadershipInfo.mkString(","))
        controllerContext.partitionLeadershipInfo.filter {
          case (topicAndPartition, leaderIsrAndControllerEpoch) =>
            leaderIsrAndControllerEpoch.leaderAndIsr.leader == id && controllerContext.partitionReplicaAssignment(topicAndPartition).size > 1
        }.map(_._1)
      }
      replicatedPartitionsBrokerLeads().toSet
    }
  }