Deadlocks in concurrent.futures.ProcessPoolExecutor with pickling error

[tomMoral]

BPO	31699
Nosy	@pitrou, @tomMoral
PRs	bpo-31699 Deadlocks in concurrent.futures.ProcessPoolExecutor with pickling error #3895 gh-75880: Deadlocks in concurrent.futures.ProcessPoolExecutor with unpickling error #4256

^{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 2018-01-05.12:33:10.791>
created_at = <Date 2017-10-05.07:41:45.845>
labels = ['3.7', 'type-bug', 'library']
title = 'Deadlocks in `concurrent.futures.ProcessPoolExecutor` with pickling error'
updated_at = <Date 2018-01-05.12:33:10.789>
user = 'https://github.com/tomMoral'

bugs.python.org fields:

activity = <Date 2018-01-05.12:33:10.789>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2018-01-05.12:33:10.791>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2017-10-05.07:41:45.845>
creator = 'tomMoral'
dependencies = []
files = []
hgrepos = []
issue_num = 31699
keywords = ['patch']
message_count = 3.0
messages = ['303745', '309497', '309504']
nosy_count = 2.0
nosy_names = ['pitrou', 'tomMoral']
pr_nums = ['3895', '4256']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31699'
versions = ['Python 3.7']

[tomMoral]

When using concurrent.futures.ProcessPoolExecutor with objects that are not picklable or unpicklable, several situations results in a deadlock, with the interpreter freezed.

This is the case for different scenario, for instance these three : https://gist.github.com/tomMoral/cc27a938d669edcf0286c57516942369

The different pickling/unpickling error and their effect should be tested in test_concurrent_futures.py

[pitrou]

New changeset 94459fd by Antoine Pitrou (Thomas Moreau) in branch 'master':
bpo-31699 Deadlocks in concurrent.futures.ProcessPoolExecutor with pickling error (bpo-3895)
94459fd

[pitrou]

This non-trivial issue has been fixed now, thanks to Thomas' patch. Thank you Thomas!