Python multiprocessing job to Celery task but Attr

Question

I made a multiprocessed function like this,

import multiprocessing
import pandas as pd
import numpy as np

def _apply_df(args):
    df, func, kwargs = args
    return df.apply(func, **kwargs)

def apply_by_multiprocessing(df, func, **kwargs):
    workers = kwargs.pop('workers')
    pool = multiprocessing.Pool(processes=workers)
    result = pool.map(_apply_df, [(d, func, kwargs)
            for d in np.array_split(df, workers)])
    pool.close()
    return pd.concat(list(result))

def square(x):
    return x**x

if __name__ == '__main__':
    df = pd.DataFrame({'a':range(10), 'b':range(10)})
    apply_by_multiprocessing(df, square, axis=1, workers=4)  
    ## run by 4 processors

Above "apply_by_multiprocessing" can execute Pandas Dataframe apply in parallel. But when I make it to Celery task, It raised AssertionError: 'Worker' object has no attribute '_config'.

from celery import shared_task

@shared_task
def my_multiple_job():
    df = pd.DataFrame({'a':range(10), 'b':range(10)})
    apply_by_multiprocessing(df, square, axis=1, workers=4)  

It's error trace is like this,

  File "/Users/yong27/work/goldstar/kinmatch/utils.py", line 14, in apply_by_multiprocessing
    pool = multiprocessing.Pool(processes=workers)
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/context.py", line 118, in Pool
    context=self.get_context())
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/pool.py", line 146, in __init__
    self._setup_queues()
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/pool.py", line 238, in _setup_queues
    self._inqueue = self._ctx.SimpleQueue()
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/context.py", line 111, in SimpleQueue
    return SimpleQueue(ctx=self.get_context())
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/queues.py", line 336, in __init__
    self._rlock = ctx.Lock()
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/context.py", line 66, in Lock
    return Lock(ctx=self.get_context())
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/synchronize.py", line 164, in __init__
    SemLock.__init__(self, SEMAPHORE, 1, 1, ctx=ctx)
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/synchronize.py", line 60, in __init__
    kind, value, maxvalue, self._make_name(),
  File "/usr/local/Cellar/python3/3.4.0/Frameworks/Python.framework/Versions/3.4/lib/python3.4/multiprocessing/synchronize.py", line 118, in _make_name
    return '%s-%s' % (process.current_process()._config['semprefix'],
AttributeError: 'Worker' object has no attribute '_config'

It seems that because Celery worker is not a normal process. How can I solve this problem? I'm using Python3.4, Django 1.6.2, celery 3.1.10, django-celery 3.1.9, pandas 0.12.0.

Answer 1

I don't know why multiprocessing doesn't work, but I recommend you to use celery group task.

from celery import task, group

def feeds_fetch(feeds):
    g = group(fetch_one.s(feed) for feed in feeds)
    g.apply_async()


@task()
def fetch_one(feed):
    return feed.fetch()

Answer 2

This issue has a good answer in this other question

Basically, it is a known issue of Celery and a dirty hack is provided: it worked for me, I just added the following code in the same file where my tasks are defined:

from celery.signals import worker_process_init
from multiprocessing import current_process

@worker_process_init.connect
def fix_multiprocessing(**kwargs):
    try:
        current_process()._config
    except AttributeError:
        current_process()._config = {'semprefix': '/mp'}