Celery 与 Flask 大型程序结构的结合

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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。