code: def _get_tracker(self, resource):
          
          with self._lock:
              for rt in self._reference_queue:
                  if rt is not None and resource is rt.resource:
                      return rt
  
          raise UnknownResourceError('Resource not created by pool')
docs: Return the resource tracker that is tracking ``resource``.
  
          :param resource: A resource.
          :return: A resource tracker.
          :rtype: :class:`_ResourceTracker`