背景
最近因项目需要，学习任务队列Celery的用法，跟着官网写Demo，出现如题错误，最终在github的Issues里找到解决办法，记录如下。
场景还原
本地环境如下：
- Windows 10
- Python 3.5.2
- Celery 4.1.0
我是跟着这个前人翻译的中文文档敲的Demo。
代码tasks.py：
from celery import Celery
app = Celery('tasks', broker='redis://:xxxx@xxx.xxx.xxx.xx:6379/0')
@app.task
def add(x, y):
return x + y
执行worker
celery -A tasks worker --loglevel=info
输出：
-------------- celery@kong9wei11 v4.1.0 (latentcall)
---- **** -----
--- * *** * -- Windows-10-10.0.14393-SP0 2018-01-12 19:01:39
-- * - **** ---
- ** ---------- [config]
- ** ---------- .> app: tasks:0x157fd248550
- ** ---------- .> transport: redis://:**@114.67.225.0:6379/0
- ** ---------- .> results: disabled://
- *** --- * --- .> concurrency: 4 (prefork)
-- ******* ---- .> task events: OFF (enable -E to monitor tasks in this worker)
--- ***** -----
-------------- [queues]
.> celery exchange=celery(direct) key=celery
[tasks]
. tasks.add
[2018-01-12 19:01:40,029: INFO/MainProcess] Connected to redis://:**@114.67.225.0:6379/0
[2018-01-12 19:01:40,130: INFO/MainProcess] mingle: searching for neighbors
[2018-01-12 19:01:40,550: INFO/SpawnPoolWorker-1] child process 9048 calling self.run()
[2018-01-12 19:01:40,557: INFO/SpawnPoolWorker-2] child process 9028 calling self.run()
[2018-01-12 19:01:40,578: INFO/SpawnPoolWorker-3] child process 13064 calling self.run()
[2018-01-12 19:01:40,611: INFO/SpawnPoolWorker-4] child process 9856 calling self.run()
[2018-01-12 19:01:41,693: INFO/MainProcess] mingle: all alone
[2018-01-12 19:01:42,212: INFO/MainProcess] celery@xx ready.
调用任务代码manager.py：
from tasks import add
add.delay(4, 4)
执行
python manager.py
然后worker里报错：
[2018-01-12 19:08:15,545: INFO/MainProcess] Received task: tasks.add[5d387722-5389-441b-9b01-a619b93b4702]
[2018-01-12 19:08:15,550: ERROR/MainProcess] Task handler raised error: ValueError('not enough values to unpack (expected 3, got 0)',)
Traceback (most recent call last):
File "d:\programmingsoftware\python35\lib\site-packages\billiard\pool.py", line 358, in workloop
result = (True, prepare_result(fun(*args, **kwargs)))
File "d:\programmingsoftware\python35\lib\site-packages\celery\app\trace.py", line 525, in _fast_trace_task
tasks, accept, hostname = _loc
ValueError: not enough values to unpack (expected 3, got 0)
解决：
原网页:Unable to run tasks under Windows
看别人描述大概就是说win10上运行celery4.x就会出现这个问题，解决办法如下,原理未知：
先安装一个`eventlet
pip install eventlet
然后启动worker的时候加一个参数，如下：
celery -A <mymodule> worker -l info -P eventlet
然后就可以正常的调用了。
运行
python manage.py
worker里输出：
[2018-01-12 19:35:33,640: INFO/MainProcess] Received task: tasks.add[3f9b5255-60a2-4a08-96b6-38f5fbc31543]
[2018-01-12 19:35:33,640: INFO/MainProcess] Task tasks.add[3f9b5255-60a2-4a08-96b6-38f5fbc31543] succeeded in 0.0s: 8
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