race condition in multiprocessing.Pool with maxtasksperchild=1

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-11-14.14:24:23.498>
labels = ['type-bug', 'library', '3.9']
title = 'race condition in multiprocessing.Pool with maxtasksperchild=1'
updated_at = <Date 2020-01-18.21:36:58.193>
user = 'https://github.com/skebanga'

bugs.python.org fields:

activity = <Date 2020-01-18.21:36:58.193>
actor = 'Jacopo Tediosi'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-11-14.14:24:23.498>
creator = 'steve.lorimer@gmail.com'
dependencies = []
files = []
hgrepos = []
issue_num = 38799
keywords = []
message_count = 2.0
messages = ['356609', '360251']
nosy_count = 2.0
nosy_names = ['steve.lorimer@gmail.com', 'Jacopo Tediosi']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38799'
versions = ['Python 3.9']