/** Topology分配线程 */
  public void init(NimbusData nimbusData) {
    this.nimbusData = nimbusData;
    this.schedulers = new HashMap<String, IToplogyScheduler>();

    IToplogyScheduler defaultScheduler = new DefaultTopologyScheduler();
    defaultScheduler.prepare(nimbusData.getConf());

    schedulers.put(DEFAULT_SCHEDULER_NAME, defaultScheduler);

    thread = new Thread(this);
    thread.setName("TopologyAssign");
    thread.setDaemon(true);
    thread.start();
  }
  /**
   * make assignments for a topology The nimbus core function, this function has been totally
   * rewrite
   *
   * @param nimbusData NimbusData
   * @param topologyId String
   * @param isScratch Boolean: isScratch is false unless rebalancing the topology
   * @throws Exception
   */
  public Assignment mkAssignment(TopologyAssignEvent event) throws Exception {
    String topologyId = event.getTopologyId();

    LOG.info("Determining assignment for " + topologyId);

    TopologyAssignContext context = prepareTopologyAssign(event);

    Set<ResourceWorkerSlot> assignments = null;

    if (!StormConfig.local_mode(nimbusData.getConf())) {

      IToplogyScheduler scheduler = schedulers.get(DEFAULT_SCHEDULER_NAME);

      assignments = scheduler.assignTasks(context);

    } else {
      assignments = mkLocalAssignment(context);
    }
    Assignment assignment = null;

    Map<String, String> nodeHost =
        getTopologyNodeHost(context.getCluster(), context.getOldAssignment(), assignments);

    Map<Integer, Integer> startTimes =
        getTaskStartTimes(context, nimbusData, topologyId, context.getOldAssignment(), assignments);

    String codeDir = StormConfig.masterStormdistRoot(nimbusData.getConf(), topologyId);

    assignment = new Assignment(codeDir, assignments, nodeHost, startTimes);

    StormClusterState stormClusterState = nimbusData.getStormClusterState();

    stormClusterState.set_assignment(topologyId, assignment);

    // update task heartbeat's start time
    NimbusUtils.updateTaskHbStartTime(nimbusData, assignment, topologyId);

    // Update metrics information in ZK when rebalance or reassignment
    // Only update metrics monitor status when creating topology
    if (context.getAssignType() == TopologyAssignContext.ASSIGN_TYPE_REBALANCE
        || context.getAssignType() == TopologyAssignContext.ASSIGN_TYPE_MONITOR)
      NimbusUtils.updateMetricsInfo(nimbusData, topologyId, assignment);
    else metricsMonitor(event);

    LOG.info("Successfully make assignment for topology id " + topologyId + ": " + assignment);

    return assignment;
  }