SystemError: Parent module 'multiprocessing' not loaded, cannot perform relative import

[AmrAli]

BPO	20633
Nosy	@brettcannon

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2014-03-23.17:23:02.583>
created_at = <Date 2014-02-15.08:08:12.087>
labels = ['type-bug', 'library']
title = "SystemError: Parent module 'multiprocessing' not loaded, cannot perform relative import"
updated_at = <Date 2014-03-23.17:23:02.582>
user = 'https://bugs.python.org/AmrAli'

bugs.python.org fields:

activity = <Date 2014-03-23.17:23:02.582>
actor = 'sbt'
assignee = 'sbt'
closed = True
closed_date = <Date 2014-03-23.17:23:02.583>
closer = 'sbt'
components = ['Library (Lib)']
creation = <Date 2014-02-15.08:08:12.087>
creator = 'Amr.Ali'
dependencies = []
files = []
hgrepos = []
issue_num = 20633
keywords = []
message_count = 3.0
messages = ['211262', '211264', '214573']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'jnoller', 'python-dev', 'sbt', 'Amr.Ali']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue20633'
versions = ['Python 3.3']

[AmrAli]

Using multiprocessing.Manager to share a dict between two processes raises the below exception at main process termination. Child process is joined and terminates gracefully before the main process.

Replacing multiprocessing/forking.py:135 with from multiprocessing.connection import wait fixes the issue.

Python 3.3.1 (default, Sep 25 2013, 19:29:01) 
[GCC 4.7.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.version
'3.3.1 (default, Sep 25 2013, 19:29:01) \n[GCC 4.7.3]'

# multiprocessing/forking.py:135

132 def wait(self, timeout=None):
133 if self.returncode is None:
134 if timeout is not None:
135 from .connection import wait
136 if not wait([self.sentinel], timeout):
137 return None
138 # This shouldn't block if wait() returned successfully.
139 return self.poll(os.WNOHANG if timeout == 0.0 else 0)
140 return self.returncode

# Traceback

Traceback (most recent call last):
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/util.py", line 255, in _run_finalizers
    finalizer()
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/util.py", line 188, in __call__
    res = self._callback(*self._args, **self._kwargs)
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/managers.py", line 588, in _finalize_manager
    process.join(timeout=1.0)
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/process.py", line 127, in join
    res = self._popen.wait(timeout)
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/forking.py", line 135, in wait
    from .connection import wait
SystemError: Parent module 'multiprocessing' not loaded, cannot perform relative import
Traceback (most recent call last):
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/util.py", line 255, in _run_finalizers
    finalizer()
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/util.py", line 188, in __call__
    res = self._callback(*self._args, **self._kwargs)
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/managers.py", line 588, in _finalize_manager
    process.join(timeout=1.0)
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/process.py", line 127, in join
    res = self._popen.wait(timeout)
  File "/home/d4de/work/redacted/redacted-engine/venv/lib/python3.3/multiprocessing/forking.py", line 135, in wait
    from .connection import wait
SystemError: Parent module 'multiprocessing' not loaded, cannot perform relative import

[AmrAli]

Also importing multiprocessing.forking at the very beginning of MyLib/init.py fixes the problem.

[python-dev]

New changeset 0b2814fc53ae by Richard Oudkerk in branch '3.3':
Issue bpo-20633: Replace relative import by absolute import.
http://hg.python.org/cpython/rev/0b2814fc53ae