pool worker can't be terminated

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-01-07.04:00:06.820>
labels = ['3.7', 'type-bug', 'library']
title = "pool worker can't be terminated"
updated_at = <Date 2021-01-15.21:53:53.632>
user = 'https://bugs.python.org/huangzhesi'

bugs.python.org fields:

activity = <Date 2021-01-15.21:53:53.632>
actor = 'ppperry'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-01-07.04:00:06.820>
creator = 'huangzhesi'
dependencies = []
files = []
hgrepos = []
issue_num = 42849
keywords = []
message_count = 3.0
messages = ['384560', '384698', '385126']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'pitrou', 'ppperry', 'davin', 'huangzhesi']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42849'
versions = ['Python 3.7']