Error in multiprocessing.Pool's initializer doesn't stop execution

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-02-23.15:55:10.770>
labels = ['type-bug', 'library', '3.9', 'docs']
title = "Error in multiprocessing.Pool's initializer doesn't stop execution"
updated_at = <Date 2021-08-23.18:43:57.347>
user = 'https://bugs.python.org/nemeskeyd'

bugs.python.org fields:

activity = <Date 2021-08-23.18:43:57.347>
actor = 'athompson6735'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Library (Lib)']
creation = <Date 2021-02-23.15:55:10.770>
creator = 'nemeskeyd'
dependencies = []
files = ['50230']
hgrepos = []
issue_num = 43306
keywords = []
message_count = 4.0
messages = ['387577', '387763', '400150', '400161']
nosy_count = 6.0
nosy_names = ['terry.reedy', 'pitrou', 'docs@python', 'nemeskeyd', 'davin', 'athompson6735']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43306'
versions = ['Python 3.9']