[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Davin Potts]

Davin Potts added the comment:

Patch committed in 2.7 branch.

Thanks for your help, Marc.

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Davin Potts]

Davin Potts added the comment:


New changeset c47c315812b1fa9acb16510a7aa3b37d113def48 by Davin Potts (Marc 
Schlaich) in branch '2.7':
bpo-26434: Fix multiprocessing grandchilds in a Windows service (GH-1167)
https://github.com/python/cpython/commit/c47c315812b1fa9acb16510a7aa3b37d113def48


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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Marc Schlaich]

Marc Schlaich added the comment:

I opened a PR on GitHub, please review.

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Roundup Robot]

Changes by Roundup Robot :


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pull_requests: +1297

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Marc Schlaich]

Marc Schlaich added the comment:

Wrong bug...

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status: closed -> open

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Marc Schlaich]

Marc Schlaich added the comment:

We have some business privilege management solution running which might have 
corrupted the installation. As no one else is reporting this issue, this is my 
best guest for this phenomena and I'm going to close this issue.

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status: open -> closed

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Marc Schlaich]

Marc Schlaich added the comment:

I can confirm that this patch is working.

Maybe the test case can be modified to simulate a "pythonservice.exe" run (by 
patching sys.executable or something like that) so it can be run without admin 
privileges.

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Davin Potts]

Davin Potts added the comment:

Attached is a patch for the 2.7 branch which adds the check described in the 
previous message.

I don't see a reasonable way to provide an accompanying test because it 
requires registering a win32 service (requiring administrative privileges) 
temporarily to attempt to provoke the issue.

Can I request that someone else run the full regression tests on this patch?  I 
am unable to complete a standard run of tests as my Windows 7 development 
system is set up for building Python 3.x (newer Visual Studio) and am hesitant 
to fight with Visual Studio configurations.

--
keywords: +patch
stage: needs patch -> patch review
Added file: 
http://bugs.python.org/file42034/issue_26434_fix_win32_service_parent_origin.patch

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Davin Potts]

Davin Potts added the comment:

I can reproduce the problem under Windows 7.  Thank you for your example and 
description -- they were very helpful.

Detection that the original parent was PythonService.exe is necessary to avoid 
undoing the paths set appropriately for running under a service.  The current 
code only detects the immediate parent.

Modifying get_preparation_data() in lib/multiprocessing/forking.py to perform 
an additional test on the inherited values from the original parent's sys.argv 
(available via the preparation_data key 'sys_argv') would resolve this:
if not d['sys_argv'][0].lower().endswith("pythonservice.exe"):


Potential complications to existing code appear very unlikely given its nature.

Patch forthcoming after running tests unless someone wants to beat me to it.

--
assignee:  -> davin
nosy: +davin
stage:  -> needs patch
type: crash -> behavior

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[issue26434] multiprocessing cannot spawn grandchild from a Windows service

[Marc Schlaich]

New submission from Marc Schlaich:

This is a follow up of #5162.

There are some occasions where you can still run into this issue. One example 
is if you want to spawn a new multiprocessing.Process as a child of a 
multiprocessing.Process:

pythonservice.exe
  - multiprocessing.Process
- multiprocessing.Process (does not start!)


Attached is a test case. If you run this in pywin32 service debug mode, you see 
that the process crashes with:

Traceback (most recent call last):
  File "", line 1, in 
  File "C:\Python27\lib\multiprocessing\forking.py", line 380, in main
prepare(preparation_data)
  File "C:\Python27\lib\multiprocessing\forking.py", line 503, in prepare
file, path_name, etc = imp.find_module(main_name, dirs)
ImportError: No module named PythonService


In get_preparation_data is the following state:

  WINSERVICE: False
  WINEXE: False
  _python_exe: C:\Python27\python.exe


And so you get as preparation data:

  {'authkey': '...', 'sys_path': [...], 'name': 'test', 'orig_dir': '...', 
'sys_argv': ['C:\\Python27\\lib\\site-packages\\win32\\PythonService.exe'], 
'main_path': 'C:\\Python27\\lib\\site-packages\\win32\\PythonService.exe', 
'log_to_stderr': False}


A workaround for me is patching `get_preparation_data` as follows:

import multiprocessing.forking

_org_get_preparation_data = multiprocessing.forking.get_preparation_data

def _get_preparation_data(*args):
data = _org_get_preparation_data(*args)
main_path = data.get('main_path')
if main_path is not None and main_path.endswith('exe'):
data.pop('main_path')
return data

multiprocessing.forking.get_preparation_data = _get_preparation_data


BTW, the test case does not run on Python 3.5, but starting the service 
manually did work. So this is probably a Python 2 issue only.

--
components: Library (Lib), Windows
files: test_mp_service.py
messages: 260846
nosy: paul.moore, schlamar, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: multiprocessing cannot spawn grandchild from a Windows service
type: crash
versions: Python 2.7
Added file: http://bugs.python.org/file42025/test_mp_service.py

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