shared memory problems with multiprocessing.Pool

[trapezoid677]

BPO	40828
Nosy	@pitrou, @applio, @vinay0410, @trapezoid677
Files	shared_memory.py

^{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 = None
created_at = <Date 2020-05-30.17:57:21.554>
labels = ['3.8', 'type-bug', 'library']
title = 'shared memory problems with multiprocessing.Pool'
updated_at = <Date 2020-07-19.07:15:02.005>
user = 'https://github.com/trapezoid677'

bugs.python.org fields:

activity = <Date 2020-07-19.07:15:02.005>
actor = 'vinay0410'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-05-30.17:57:21.554>
creator = 'trapezoid677'
dependencies = []
files = ['49203']
hgrepos = []
issue_num = 40828
keywords = []
message_count = 2.0
messages = ['370396', '373938']
nosy_count = 4.0
nosy_names = ['pitrou', 'davin', 'vinay0410', 'trapezoid677']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40828'
versions = ['Python 3.8']

[trapezoid677]

Under Linux, the resource_tracker throws warnings about not released memory blocks after the programs has finished and when used together with multiprocessing.Pool. This depends on the sequence of initialization of the shared memory block and the multiprocessing pool. In addition, .close() on the shared memory block generates a segmentation fault in the example code.

Under MS Windows, the shared memory block holds arbitrary values when being read in the worker routines, but no warnings are thrown and no segmentation fault occurs when closing the memory block.

[vinay0410]

Hi, Can you please confirm the python version in which you replicated this issue. I tried replicating (segmentation fault) this issue in python 3.8.0b3 but didn't succeed. And shared_memory isn't present in 3.7. Also, shared_memory is known to throw some warnings, and there is already a PR and issue open for that https://bugs.python.org/issue38119.