multiprocessing.Pool deadlocks with only print statements

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-04-29.22:52:09.928>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'multiprocessing.Pool deadlocks with only print statements'
updated_at = <Date 2020-04-30.22:45:06.357>
user = 'https://bugs.python.org/DarinTay'

bugs.python.org fields:

activity = <Date 2020-04-30.22:45:06.357>
actor = 'ned.deily'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-04-29.22:52:09.928>
creator = 'DarinTay'
dependencies = []
files = []
hgrepos = []
issue_num = 40444
keywords = []
message_count = 3.0
messages = ['367712', '367718', '367719']
nosy_count = 4.0
nosy_names = ['tim.peters', 'pitrou', 'davin', 'DarinTay']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40444'
versions = ['Python 3.7', 'Python 3.8']