def _close_cursor(self, cursor_id, address):
        """Send a kill cursors message with the given id.

        What closing the cursor actually means depends on this client's
        cursor manager. If there is none, the cursor is closed asynchronously
        on a background thread.
        """
        if self.__cursor_manager is not None:
            self.__cursor_manager.close(cursor_id, address)
        else:
            self.__kill_cursors_queue.append((address, [cursor_id]))
Send a kill cursors message with the given id.

        What closing the cursor actually means depends on this client's
        cursor manager. If there is none, the cursor is closed asynchronously
        on a background thread.
        
stackoverflow/venv/lib/python3.6/site-packages/pymongo/mongo_client.py