Can't use XMLRPC errors with multiprocessing and pickle

Can't use XMLRPC errors with multiprocessing and pickle modules. Multiprocessing freezes.

Bug example

from multiprocessing import Pool
from xmlrpc.client import ProtocolError


def raise_error(_):
    raise ProtocolError("1", 2, "3", {})


Pool(1).map(raise_error, (["A", 5]))

Expected output

Traceback (most recent call last):
  File "C:\Program Files\Python310\lib\multiprocessing\pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "C:\Program Files\Python310\lib\multiprocessing\pool.py", line 48, in mapstar
    return list(map(*args))
  File "C:\Users\ppatrin\Projects\test.py", line 6, in raise_error
    raise ProtocolError("1", 2, "3", {})
xmlrpc.client.ProtocolError: <ProtocolError for 1: 2 3>

Actual output

"C:\Program Files\Python310\python.exe" C:/Users/ppatrin/Projects/test.py
Exception in thread Thread-3 (_handle_results):
Traceback (most recent call last):
  File "C:\Program Files\Python310\lib\threading.py", line 1009, in _bootstrap_inner
    self.run()
  File "C:\Program Files\Python310\lib\threading.py", line 946, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Program Files\Python310\lib\multiprocessing\pool.py", line 576, in _handle_results
    task = get()
  File "C:\Program Files\Python310\lib\multiprocessing\connection.py", line 256, in recv
    return _ForkingPickler.loads(buf.getbuffer())
TypeError: ProtocolError.__init__() missing 4 required positional arguments: 'url', 'errcode', 'errmsg', and 'headers'

And multiprocessing processes frozes.

Real problem

import pickle
from xmlrpc.client import ProtocolError

pickle.loads(pickle.dumps(ProtocolError(1, "2", 3, {})))

>>> TypeError: __init__() missing 4 required positional arguments: 'url', 'errcode', 'errmsg', and 'headers'

How to fix

We should fix a super call in exception method initializer.

class ProtocolError(Error):
    """Indicates an HTTP protocol error."""
    def __init__(self, url, errcode, errmsg, headers):
---        Error.__init__(self)
+++        Error.__init__(self, url, errcode, errmsg, headers)
        self.url = url
        self.errcode = errcode
        self.errmsg = errmsg
        self.headers = headers

Your environment

• CPython versions tested on: 3.10.4
• Operating system and architecture: Windows 11 and Ubuntu 20.04.

Commencez par l’initialiseur de ProtocolError dans le module xmlrpc.client et reproduisez l’aller-retour avec pickle présenté dans l’issue. Le travail est terminé lorsque ProtocolError peut être sérialisée et désérialisée avec succès et que l’exemple de multiprocessing ne se fige plus lors du renvoi de l’erreur attendue.