code: def invalidate_object(self, address, state = 'stale'):
          
          self._lock.acquire()
          try:
              item = self.get_item(address)
              if item and item.state_value<_state_values[state]:
                  item.state=state
                  item.update_state()
                  self._items_list.sort()
          finally:
              self._lock.release()
docs: Force cache item state change (to 'worse' state only).
  
          :Parameters:
              - `state`: the new state requested.
          :Types:
              - `state`: `str`