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multiprocessing.Pool.__enter__() should raise an exception if called twice #79658

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vstinner opened this issue Dec 12, 2018 · 3 comments
Closed

multiprocessing.Pool.__enter__() should raise an exception if called twice #79658

vstinner opened this issue Dec 12, 2018 · 3 comments
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3.8 only security fixes stdlib Python modules in the Lib dir

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@vstinner
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BPO 35477
Nosy @vstinner
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  • bpo-35477: multiprocessing.Pool.__enter__() fails if called twice #11134
    		•

    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 2018-12-13.01:15:47.499>
created_at = <Date 2018-12-12.23:08:12.351>
labels = ['3.8', 'library']
title = 'multiprocessing.Pool.__enter__() should raise an exception if called twice'
updated_at = <Date 2018-12-13.01:15:47.498>
user = 'https://github.com/vstinner'

    bugs.python.org fields:

    activity = <Date 2018-12-13.01:15:47.498>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2018-12-13.01:15:47.499>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2018-12-12.23:08:12.351>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 35477
keywords = ['patch']
message_count = 3.0
messages = ['331719', '331720', '331728']
nosy_count = 1.0
nosy_names = ['vstinner']
pr_nums = ['11134']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue35477'
versions = ['Python 3.8']
    @vstinner
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    On a file, "with file:" fails if it's used a second time:
    ---

    fp = open('/etc/issue')
with fp:
    print("first")
with fp:
    print("second")

    fails with "ValueError: I/O operation on closed file", because file.__enter__() raises this exception if the file is closed.

    I propose to have the same behavior on multiprocessing.Pool.__enter__() to detect when the multiprocessing API is misused.

    Anyway, after the first "with pool:" block, the pool becomes unusable to schedule now tasks: apply() raise ValueError("Pool not running") in that case for example.

    @vstinner vstinner added 3.8 only security fixes stdlib Python modules in the Lib dir labels Dec 12, 2018
    @vstinner
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    Currently, the error only occurs when apply() is called:
    ---

    import multiprocessing

def the_test():
    pool = multiprocessing.Pool(1)
    with pool:
        print(pool.apply(int, (2,)))
    with pool:
        print(pool.apply(int, (3,))) # <-- raise here

the_test()

    I would prefer to get an error on at the second "with pool:" line.

    @vstinner
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    New changeset 08c2ba0 by Victor Stinner in branch 'master':
    bpo-35477: multiprocessing.Pool.__enter__() fails if called twice (GH-11134)
    08c2ba0

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