Celery 与 Flask 大型程序结构的结合

2022-03-09 01:13:16

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Celery 与 Flask 大型程序结构结合的关键：

使 Celery 与 Flask 结合的关键在于非 Web Runtime 中调取上下文。

因为当 Flask App 在作为 WSGI Application 运行时，会在每个请求进入的时候将请求上下文推入 _request_ctx_stack 中。推入请求上下文的同时，将检查应用上下文堆栈 _app_ctx_stack 是否为空，若空则隐式地推入一个应用上下文。最终，在请求线程退出前，应用上下文将从其 Flask._app_ctx_stack 的栈中里弹出。

Celery 作为任务调度模块，其任务执行单元（worker）运行时，将处于非 Web Runtime 的状态，而此时应用上下文堆栈 Flask._app_ctx_stack 为空，因此调取上下文将引发"RunTimeError"的报错。

Flask 大型程序结构下，采用工厂函数（create_app）创建 Flask App，因此同样采用工厂函数的形式创建 Celery App，其工厂函数如下：

from celery import Celery

def make_celery(App):

CeleryInst = Celery(App.import_name, backend = App.config['CELERY_RESULT_BACKEND'], broker = App.config['CELERY_BROKER_URL'])

CeleryInst.conf.update(App.config)

TaskBase = CeleryInst.Task

class ContextTask(TaskBase):

"""Will be execute when create the instance object of ContextTasks."""

# Will context(Flask's Extends) of app object(Producer Sit)

# be included in celery object(Consumer Site).

abstract = True

def __call__(self, *args, **kwargs):

with App.app_context():

return TaskBase.__call__(self, *args, **kwargs)

# Include the app_context into celery.Task.

# Let other Flask extensions can be normal calls.

CeleryInst.Task = ContextTask

return CeleryInst

注意：此方式创建 Celery 对象时，将会把用于初始化的 Flask App 的上下文信息包含至 Celery 对象中。基于此，Flask 扩展在调用 Celery 任务时，采用最普通的方式，而不需额外考虑上下文问题。

Celery 与 Flask 大型程序结构结合的实例：

Flask 大型程序结构如下。

|-flasky

|-app/

|-templates/

|-static/

|-main/

|-__init__.py

|-errors.py

|-forms.py

|-views.py

|-__init__.py

|-mail/

|-templates/

|-__init__.py

|-mail.py

|-migrations/

|-tests/

|-__init__.py

|-test*.py

|-venv/

|-requirements.txt

|-config.py

|-manage.py

注意：与原 Flask 大型程序结构作出如下修改以及强调。

(1).Flask App 及 Celery App 创建于 /flasky/app/__init__.py 中。

(2).manage.py 中通过 import 方式引入 Flask App，并在该文件中启用 WSGI。

(3).在其他需要调用 Flask App 的地方，采用 current_app._get_current_object() 实现。

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