code: private void addMapTask(TaskTracker taskTracker, List<Task> tasks, 
                                int maxMapSlots, int currentMapSlots)
                      throws IOException {
      if (maxMapSlots > currentMapSlots) {
        mapScheduler.updateCollectionOfQSIs();
        TaskLookupResult tlr = mapScheduler.assignTasks(taskTracker);
        if (TaskLookupResult.LookUpStatus.TASK_FOUND == tlr.getLookUpStatus()) {
          tasks.add(tlr.getTask());
        }
      }
    }
docs: on the TT to run one.