使用SQLite作为代理的Celery + Flask,在调用任务时出错

我正在尝试让Flask与Ceite一起使用SQLite作为后端.但是,使用以下代码:

CELERY_BROKER_URL = 'sqla+sqlite:///' + os.path.join(basedir, 'celery.db')

def make_celery(app):
    celery = Celery(app.import_name, broker=app.config['CELERY_BROKER_URL'])
    celery.conf.update(app.config)
    TaskBase = celery.Task
    class ContextTask(TaskBase):
        abstract = True
        def __call__(self, *args, **kwargs):
            with app.app_context():
                return TaskBase.__call__(self, *args, **kwargs)
    celery.Task = ContextTask
    return celery

启动一个worker后,我在尝试调用一个虚拟任务时遇到这个错误:

error: [Errno 10061] No connection could be made because the target machine actively refused it

码:

@app.route('/test')
def test():
    t = add_together.delay(100,200)
    return str(t.wait())

怎么了？我已经尝试使用Google搜索Sqllite/SQLAlchemy/Flask/Celery的任意组合,但一直无法找到解决方案.