celery应用--周期性任务

目标：使用celery实现一个周期性任务，每隔10s打印一次"hello,world"
1.创建一个目录my_scheduler
2.在该目录下创建两个文件
test/my_scheduler/celery.py

from celery import Celery

app = Celery('my_scheduler', broker='redis://127.0.0.1:6379/0', backend='redis://127.0.0.1:6379/0')
app.autodiscover_tasks(['my_scheduler.celery_task'])

app.conf.beat_schedule = {
    'hello-every-10-seconds': {
        'task': 'my_scheduler.celery_task.hello',
        'schedule': 10.0,
    },
}

test/my_scheduler/celery_task.py

from celery import Celery
from celery.schedules import crontab

# app = Celery('my_scheduler', broker='redis://localhost:6379/0')
from celery import shared_task


@shared_task
def hello():
    print('Hello, world!')

3.在test下执行

celery -A my_scheduler worker -l info -P eventlet
celery -A my_scheduler beat

遇到问题1：
app.autodiscover_task()执行报错

Received unregistered task of type 'my_scheduler.celery_task.hello'.
The message has been ignored and discarded.

Did you remember to import the module containing this task?
Or maybe you're using relative imports?

Please see
http://docs.celeryq.org/en/latest/internals/protocol.html
for more information.

可以看到是因为发送的任务未注册导致，需要指定注册的目录：app.autodiscover_tasks([‘my_scheduler.celery_task’])

遇到问题2：
celery -A my_scheduler worker -l info启动任务报错

[2023-09-18 15:22:02,071: INFO/MainProcess] Task my_scheduler.celery_task.hello[88cf347f-5766-4cac-9816-e832f90d2c4a] received
[2023-09-18 15:22:02,113: ERROR/MainProcess] Task handler raised error: ValueError('not enough values to unpack (expected 3, got 0)')
Traceback (most recent call last):
  File "D:\APP_install\python\lib\site-packages\billiard\pool.py", line 362, in workloop
    result = (True, prepare_result(fun(*args, **kwargs)))
  File "D:\APP_install\python\lib\site-packages\celery\app\trace.py", line 638, in fast_trace_task
    tasks, accept, hostname = _loc
ValueError: not enough values to unpack (expected 3, got 0) 

查询原因：
Eventlet has an issue on subprocess.CalledProcessError:

https://github.com/celery/celery/issues/4063

https://github.com/eventlet/eventlet/issues/357

https://github.com/eventlet/eventlet/issues/413

解决方法：

pip install gevent
celery -A <module> worker -l info -P gevent