Kafka GroupCoordinator机制(十六)：GroupCoordinator之LeaveGroupRequest分析

消费者离开消费者组是向GroupCoordinator发送LeaveGroupRequest。

  def handleLeaveGroup(groupId: String, consumerId: String, responseCallback: Short => Unit) {
    if (!isActive.get) {
      responseCallback(Errors.GROUP_COORDINATOR_NOT_AVAILABLE.code)
    } else if (!isCoordinatorForGroup(groupId)) {
      responseCallback(Errors.NOT_COORDINATOR_FOR_GROUP.code)
    } else if (isCoordinatorLoadingInProgress(groupId)) {
      responseCallback(Errors.GROUP_LOAD_IN_PROGRESS.code)
    } else {
      val group = groupManager.getGroup(groupId)
      if (group == null) {
        // if the group is marked as dead, it means some other thread has just removed the group
        // from the coordinator metadata; this is likely that the group has migrated to some other
        // coordinator OR the group is in a transient unstable phase. Let the consumer to retry
        // joining without specified consumer id,
        responseCallback(Errors.UNKNOWN_MEMBER_ID.code)
      } else {
        group synchronized {
          if (group.is(Dead)) {
              //如果遇到Group处于Dead、未知的memberID，就调用回调函数返回错误码
            responseCallback(Errors.UNKNOWN_MEMBER_ID.code)
          } else if (!group.has(consumerId)) {
            responseCallback(Errors.UNKNOWN_MEMBER_ID.code)
          } else {
            val member = group.get(consumerId)
            removeHeartbeatForLeavingMember(group, member)
            // 移除memberMetadata对象并完成状态转化
            onMemberFailure(group, member)
            responseCallback(Errors.NONE.code)
          }
        }
      }
    }
  }

  private def onMemberFailure(group: GroupMetadata, member: MemberMetadata) {
    trace("Member %s in group %s has failed".format(member.memberId, group.groupId))
    group.remove(member.memberId)
    group.currentState match {
      case Dead =>
      case Stable | AwaitingSync => maybePrepareRebalance(group)
      case PreparingRebalance => joinPurgatory.checkAndComplete(GroupKey(group.groupId))
    }
  }