celery —— 任务调用方式

实际上 delay 只是 apply_async 的快捷方式，二者作用相同，只是 apply_async 可以进行更多的任务属性设置，比如 callbacks/errbacks 正常回调与错误回调、执行超时、重试、重试时间等等

celery\app\task.py 中的Task类下的delay方法

class Task(object):

    def delay(self, *args, **kwargs):
        """Star argument version of :meth:`apply_async`.

        Does not support the extra options enabled by :meth:`apply_async`.
    
        Arguments:
            *args (Any): Positional arguments passed on to the task.
            **kwargs (Any): Keyword arguments passed on to the task.
        eturns:
            celery.result.AsyncResult: Future promise.
        """
        return self.apply_async(args, kwargs)

def apply_async(self, args=None, kwargs=None, task_id=None, producer=None,
 link=None, link_error=None, shadow=None, **options):
......

return app.send_task(
    self.name, args, kwargs, task_id=task_id, producer=producer,
 link=link, link_error=link_error, result_cls=self.AsyncResult,
 shadow=shadow, task_type=self,
 **options
)

def send_task(self, name, args=None, kwargs=None, countdown=None,
 eta=None, task_id=None, producer=None, connection=None,
 router=None, result_cls=None, expires=None,
 publisher=None, link=None, link_error=None,
 add_to_parent=True, group_id=None, retries=0, chord=None,
 reply_to=None, time_limit=None, soft_time_limit=None,
 root_id=None, parent_id=None, route_name=None,
 shadow=None, chain=None, task_type=None, **options):

......

result = (result_cls or self.AsyncResult)(task_id)
......

return result

delay 返回的是一个 AsyncResult 对象，里面存的就是一个异步的结果，当任务完成时result.ready() 为 true，然后用 result.get() 取结果即可。

#官方文档
apply_async() and Task.delay() will return an EagerResult instance, that emulates the API and behavior of AsyncResult, except the result is already evaluated.