Notify of configuration update through file.

    Arguments:
        state (_WaffleState): Object that contains reference to app and its
            configstore.

def _file_notifier(state):
    """Notify of configuration update through file.

    Arguments:
        state (_WaffleState): Object that contains reference to app and its
            configstore.
    """
    tstamp = time.time()
    state._tstamp = tstamp
    conf = state.app.config

    file_path = conf.get('WAFFLE_WATCHER_FILE', '/tmp/waffleconf.txt')

    if not os.path.isfile(file_path):
        # Create watch file
        open(file_path, 'a').close()

    # Update timestamp
    os.utime(file_path, (tstamp, tstamp))