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Unexpected behavior for 0 or negative processes in multiprocessing.pool() #56494

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jorgsk mannequin opened this issue Jun 8, 2011 · 6 comments
Closed

Unexpected behavior for 0 or negative processes in multiprocessing.pool() #56494

jorgsk mannequin opened this issue Jun 8, 2011 · 6 comments
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stdlib Python modules in the Lib dir

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@jorgsk
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jorgsk mannequin commented Jun 8, 2011

BPO 12285
Nosy @jaraco, @vstinner, @vadmium
Files
  • multitest_pool.py
  • multiprocessing_pool.patch
    		•

    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 2011-06-20.15:56:45.588>
created_at = <Date 2011-06-08.13:55:28.529>
labels = ['library']
title = 'Unexpected behavior for 0 or negative processes in multiprocessing.pool()'
updated_at = <Date 2016-09-02.02:20:26.408>
user = 'https://bugs.python.org/jorgsk'

    bugs.python.org fields:

    activity = <Date 2016-09-02.02:20:26.408>
actor = 'jaraco'
assignee = 'none'
closed = True
closed_date = <Date 2011-06-20.15:56:45.588>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2011-06-08.13:55:28.529>
creator = 'jorgsk'
dependencies = []
files = ['22283', '22287']
hgrepos = []
issue_num = 12285
keywords = ['patch']
message_count = 6.0
messages = ['137908', '137933', '138735', '274192', '274194', '274198']
nosy_count = 5.0
nosy_names = ['jaraco', 'vstinner', 'python-dev', 'jorgsk', 'martin.panter']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue12285'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3']
    @jorgsk
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    jorgsk mannequin commented Jun 8, 2011

    A normal way to start a multiprocessing-pool is like this:

    Multiprocessing.Pool(processes=some_number).

    However, if 'some_number' is 0 or negative, Python hangs and must be killed. I would expect an error message of the type: "Number of processes must be at least 1".

    Attaching a script that reproduces this.

    I struggled a bit with this for a program that uses cpu_count() - 4 to calculate 'some_number'. Guess what happens when the number of cores is 4 :) Even though the fix is easy (if some_number < 1), it would be nice to be warned about it.

    @jorgsk jorgsk mannequin added the stdlib Python modules in the Lib dir label Jun 8, 2011
    @vstinner
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    vstinner commented Jun 9, 2011

    multiprocessing_pool.patch: raise a ValueError if processes is less than 1. A test should be added.

    @python-dev
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    python-dev mannequin commented Jun 20, 2011

    New changeset 1f171dd21bdb by Victor Stinner in branch '3.2':
    Issue bpo-12285: multiprocessing.Pool() raises a ValueError if the number of
    http://hg.python.org/cpython/rev/1f171dd21bdb

    New changeset 1861683793d9 by Victor Stinner in branch 'default':
    (merge 3.2) Issue bpo-12285: multiprocessing.Pool() raises a ValueError if the
    http://hg.python.org/cpython/rev/1861683793d9

    New changeset 815263546757 by Victor Stinner in branch '2.7':
    Issue bpo-12285: multiprocessing.Pool() raises a ValueError if the number of
    http://hg.python.org/cpython/rev/815263546757

    @python-dev
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    python-dev mannequin commented Sep 2, 2016

    New changeset 941346104718 by Jason R. Coombs in branch '3.4':
    Issue bpo-12285: Add test capturing failure.
    https://hg.python.org/cpython/rev/941346104718

    New changeset 56c60b3d06fb by Jason R. Coombs in branch '3.4':
    Issue bpo-12285: Replace implementation of findall with implementation from Setuptools 7ce820d524db.
    https://hg.python.org/cpython/rev/56c60b3d06fb

    New changeset 13619a3e0737 by Jason R. Coombs in branch '3.4':
    Issue bpo-12285: Update NEWS
    https://hg.python.org/cpython/rev/13619a3e0737

    New changeset ade53661607a by Jason R. Coombs in branch '3.5':
    Issue bpo-12285: Merge with 3.4
    https://hg.python.org/cpython/rev/ade53661607a

    @vadmium
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    vadmium commented Sep 2, 2016

    Looks like that last lot was meant to reference bpo-12885

    @jaraco
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    jaraco commented Sep 2, 2016

    Yep. Sorry for the misfile.

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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