[issue35919] multiprocessing: shared manager Pool fails with AttributeError

[Felipe A. Hernandez]

Felipe A. Hernandez <ergoithz at gmail.com> added the comment:

import traceback
import multiprocessing.managers


class MyManager(multiprocessing.managers.SyncManager):
    pass

class DictList(multiprocessing.managers.BaseProxy):
    _method_to_typeid_ = {'__getitem__': 'dict'}

    def __getitem__(self, key):
        return self._callmethod('__getitem__', (key,))

MyManager.register('DictList', None, DictList)

with MyManager() as manager:

    nested = manager.DictList([{'hello': 'world'}])
    print(nested[0]['hello'])  # world

    proxy = manager.list([nested])
    try:
        print(proxy[0][0]['hello'])
    except AttributeError:
        traceback.print_exc()
        print("""
        Bug: AttributeError: ProxyBase._callmethod is None
        --------------------------------------------------

        This error is raised because proxies returned as #RETURN messages
        have no manager reference, which is required to resolve typeids
        (using BaseManager._registry).

        Only proxies returned as #PROXY messages will be fully functional.

        This is an undocumented current implementation limitation.

        Fix (proposal)
        --------------

        Include the manager class (not the instance) as part of the proxy
        serialization in BaseProxy.__reduce__, as BaseManager._registry is
        a class variable.

        Note: #PROXY message protocol can be also replaced by regular proxy
              serialization after this fix, resulting on simpler codebase.
        """)

----------
nosy: +Felipe A. Hernandez

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35919>
_______________________________________