code: void createTaskEntry(TaskAttemptID taskid, String taskTracker, TaskInProgress tip) {
      LOG.info("Adding task (" + tip.getAttemptType(taskid) + ") " +
        "'"  + taskid + "' to tip " +
        tip.getTIPId() + ", for tracker '" + taskTracker + "'");
  
      // taskid --> tracker
      taskidToTrackerMap.put(taskid, taskTracker);
  
      // tracker --> taskid
      Set<TaskAttemptIDWithTip> taskset = trackerToTaskMap.get(taskTracker);
      if (taskset == null) {
        taskset = new HashSet<TaskAttemptIDWithTip>();
        trackerToTaskMap.put(taskTracker, taskset);
      }
      taskset.add(new TaskAttemptIDWithTip(taskid, tip));
  
      // taskid --> TIP
      taskidToTIPMap.put(taskid, tip);
  
    }
docs: /////////////////////////////////////////////////////