'Note that we\'ve changed this index (so it can be saved as
appropriate).'

def changed_index(self, dir, index_name):

    self._acquire_lock()
    try:
        now = time.time()
        dbsubpath = join(self.db.dhash_from_dir(dir), index_name)
        self._index_and_atime_from_dbsubpath[dbsubpath][1] = now
        self._is_index_dirty_from_dbsubpath[dbsubpath] = True
    finally:
        self._release_lock()
