KafkaController之重新被选为leader

在之前的leader选举过程一文当中说到当在选举过程当中发生异常时，会重新选举leader，这时候会触发LeaderChangeListener的handleDataDeleted方法，如果此时当前broker重新被选为leader，则会回调onControllerResignation：

//当前broker重新被选举为controller
def onControllerResignation() {
    // de-register listeners
    deregisterReassignedPartitionsListener()
    deregisterPreferredReplicaElectionListener()

    // shutdown delete topic manager
    if (deleteTopicManager != null)
      deleteTopicManager.shutdown()

    // shutdown leader rebalance scheduler
    if (config.autoLeaderRebalanceEnable)
      autoRebalanceScheduler.shutdown()

    inLock(controllerContext.controllerLock) {
      // de-register partition ISR listener for on-going partition reassignment task
      deregisterReassignedPartitionsIsrChangeListeners()
      // shutdown partition state machine
      partitionStateMachine.shutdown()
      // shutdown replica state machine
      replicaStateMachine.shutdown()
      // shutdown controller channel manager
      if(controllerContext.controllerChannelManager != null) {
        controllerContext.controllerChannelManager.shutdown()
        controllerContext.controllerChannelManager = null
      }
      // reset controller context
      controllerContext.epoch=0
      controllerContext.epochZkVersion=0
      brokerState.newState(RunningAsBroker)

      info("Broker %d resigned as the controller".format(config.brokerId))
    }
}

该方法主要做以下几件事情：

1.清除/admin/reassign_partitions路径的PartitionsReassignedListener。

2.清除/admin/preferred_replica_election路径的PreferredReplicaElectionListener。

3.清除/brokers/topics/topic/partitions/partitionId/state路径的ReassignedPartitionsIsrChangeListener。

这几个listener的作用在上文都有说过。

清除之前leader遗留的状态后会在leader选举时重新调用elect方法：

def handleDataDeleted(dataPath: String) {
      inLock(controllerContext.controllerLock) {
        debug("%s leader change listener fired for path %s to handle data deleted: trying to elect as a leader"
          .format(brokerId, dataPath))
        if(amILeader)
          onResigningAsLeader()//被重新选为leader
        elect
      }
}

elect方法又会回调onControllerFailover方法重新为leader设置一些必要的数据结构及相关路径的listener（具体见上文）。