[New-bugs-announce] [issue27649] multiprocessing on Windows does not properly manage class attributes

[Ian Cordasco]

New submission from Ian Cordasco:

In trying to add support for multiprocessing on Windows in Flake8, I found that the behaviour of the module is significantly different than on Unix. If you have a class that has class-level attributes on Unix, and you change them, put the class into a Queue (or have it attached to an object that moves through a Queue) then the values you set will be preserved [1]. On Windows [2], the attributes are reset.


As a minimal reproduction, I've thrown together this project: https://github.com/sigmavirus24/windows-multiprocessing-bug which is running tox on AppVeyor (https://ci.appveyor.com/project/sigmavirus24/windows-multiprocessing-bug) and Travis CI (https://travis-ci.org/sigmavirus24/windows-multiprocessing-bug) so the behaviours can be compared.

For application developers, it would be wonderful if we could rely on the standard library behaving the same way in this case across both operating systems.

[1] https://travis-ci.org/sigmavirus24/windows-multiprocessing-bug/jobs/148276925#L158 https://travis-ci.org/sigmavirus24/windows-multiprocessing-bug/jobs/148276926#L158 https://travis-ci.org/sigmavirus24/windows-multiprocessing-bug/jobs/148276927#L157

[2] https://ci.appveyor.com/project/sigmavirus24/windows-multiprocessing-bug/build/1.0.2#L24

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components: Windows
messages: 271618
nosy: icordasc, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: multiprocessing on Windows does not properly manage class attributes
type: behavior
versions: Python 3.3, Python 3.4, Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27649>
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