@Override
  public void handle(TaskSchedulerEvent event) {
    if (event.getType() == EventType.T_SCHEDULE) {
      if (event instanceof FragmentScheduleEvent) {
        FragmentScheduleEvent castEvent = (FragmentScheduleEvent) event;
        if (context.isLeafQuery()) {
          TaskAttemptScheduleContext taskContext = new TaskAttemptScheduleContext();
          Task task = Stage.newEmptyTask(context, taskContext, stage, nextTaskId++);
          task.addFragment(castEvent.getLeftFragment(), true);
          scheduledObjectNum++;
          if (castEvent.hasRightFragments()) {
            task.addFragments(castEvent.getRightFragments());
          }
          stage.getEventHandler().handle(new TaskEvent(task.getId(), TaskEventType.T_SCHEDULE));
        } else {
          fragmentsForNonLeafTask = new FileFragment[2];
          fragmentsForNonLeafTask[0] = castEvent.getLeftFragment();
          if (castEvent.hasRightFragments()) {
            Collection<Fragment> var = castEvent.getRightFragments();
            FileFragment[] rightFragments = var.toArray(new FileFragment[var.size()]);
            fragmentsForNonLeafTask[1] = rightFragments[0];
            if (rightFragments.length > 1) {
              broadcastFragmentsForNonLeafTask = new FileFragment[rightFragments.length - 1];
              System.arraycopy(
                  rightFragments,
                  1,
                  broadcastFragmentsForNonLeafTask,
                  0,
                  broadcastFragmentsForNonLeafTask.length);
            } else {
              broadcastFragmentsForNonLeafTask = null;
            }
          }
        }
      } else if (event instanceof FetchScheduleEvent) {
        FetchScheduleEvent castEvent = (FetchScheduleEvent) event;
        Map<String, List<FetchImpl>> fetches = castEvent.getFetches();
        TaskAttemptScheduleContext taskScheduleContext = new TaskAttemptScheduleContext();
        Task task = Stage.newEmptyTask(context, taskScheduleContext, stage, nextTaskId++);
        scheduledObjectNum++;
        for (Entry<String, List<FetchImpl>> eachFetch : fetches.entrySet()) {
          task.addFetches(eachFetch.getKey(), eachFetch.getValue());
          task.addFragment(fragmentsForNonLeafTask[0], true);
          if (fragmentsForNonLeafTask[1] != null) {
            task.addFragment(fragmentsForNonLeafTask[1], true);
          }
        }
        if (broadcastFragmentsForNonLeafTask != null
            && broadcastFragmentsForNonLeafTask.length > 0) {
          task.addFragments(Arrays.asList(broadcastFragmentsForNonLeafTask));
        }
        stage.getEventHandler().handle(new TaskEvent(task.getId(), TaskEventType.T_SCHEDULE));
      } else if (event instanceof TaskAttemptToSchedulerEvent) {
        TaskAttemptToSchedulerEvent castEvent = (TaskAttemptToSchedulerEvent) event;
        if (context.isLeafQuery()) {
          scheduledRequests.addLeafTask(castEvent);
        } else {
          scheduledRequests.addNonLeafTask(castEvent);
        }

        if (needWakeup.getAndSet(false)) {
          // wake up scheduler thread after scheduled
          synchronized (schedulingThread) {
            schedulingThread.notifyAll();
          }
        }
      }
    } else if (event.getType() == EventType.T_SCHEDULE_CANCEL) {
      // when a stage is killed, unassigned query unit attmpts are canceled from the scheduler.
      // This event is triggered by TaskAttempt.
      TaskAttemptToSchedulerEvent castedEvent = (TaskAttemptToSchedulerEvent) event;
      scheduledRequests.leafTasks.remove(castedEvent.getTaskAttempt().getId());
      LOG.info(
          castedEvent.getTaskAttempt().getId()
              + " is canceled from "
              + this.getClass().getSimpleName());
      ((TaskAttemptToSchedulerEvent) event)
          .getTaskAttempt()
          .handle(
              new TaskAttemptEvent(
                  castedEvent.getTaskAttempt().getId(), TaskAttemptEventType.TA_SCHEDULE_CANCELED));
    }
  }
    private void addLeafTask(TaskAttemptToSchedulerEvent event) {
      TaskAttempt taskAttempt = event.getTaskAttempt();
      List<DataLocation> locations = taskAttempt.getTask().getDataLocations();

      for (DataLocation location : locations) {
        String host = location.getHost();
        leafTaskHosts.add(host);

        HostVolumeMapping hostVolumeMapping = leafTaskHostMapping.get(host);
        if (hostVolumeMapping == null) {
          String rack = RackResolver.resolve(host).getNetworkLocation();
          hostVolumeMapping = new HostVolumeMapping(host, rack);
          leafTaskHostMapping.put(host, hostVolumeMapping);
        }
        hostVolumeMapping.addTaskAttempt(location.getVolumeId(), taskAttempt);

        if (LOG.isDebugEnabled()) {
          LOG.debug("Added attempt req to host " + host);
        }

        HashSet<TaskAttemptId> list = leafTasksRackMapping.get(hostVolumeMapping.getRack());
        if (list == null) {
          list = new HashSet<>();
          leafTasksRackMapping.put(hostVolumeMapping.getRack(), list);
        }

        list.add(taskAttempt.getId());

        if (LOG.isDebugEnabled()) {
          LOG.debug("Added attempt req to rack " + hostVolumeMapping.getRack());
        }
      }

      leafTasks.add(taskAttempt.getId());
    }
 private void addNonLeafTask(TaskAttemptToSchedulerEvent event) {
   nonLeafTasks.add(event.getTaskAttempt().getId());
 }