code: public boolean isModified(boolean isAsync)
    {
      long now = CurrentTime.currentTime();
  
      if (now < _checkExpiresTime)
        return _isModified;
      
      if (_isChecking.getAndSet(true))
        return _isModified;
      
      _checkExpiresTime = now + _checkInterval;
  
      if (isAsync) {
        getWorker().wake();
      }
      else {
        try {
          checkImpl();
        } finally {
          _isChecking.set(false);
        }
      }
  
      return _isModified;
    }
docs: Returns true if the underlying dependencies have changed.