docs: private AtomicBoolean getPushingFlag(TaskTrackerNode taskTrackerNode) {
          AtomicBoolean flag = PUSHING_FLAG.get(taskTrackerNode.getIdentity());
          if (flag == null) {
              flag = new AtomicBoolean(false);
              AtomicBoolean exist = PUSHING_FLAG.putIfAbsent(taskTrackerNode.getIdentity(), flag);
              if (exist != null) {
                  flag = exist;
              }
          }
          return flag;
      }