Multi-threaded circular import fails with _DeadlockError when using importlib

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-09-10.19:10:54.811>
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = 'Multi-threaded circular import fails with _DeadlockError when using importlib'
updated_at = <Date 2019-09-10.19:10:54.811>
user = 'https://github.com/rlamy'

bugs.python.org fields:

activity = <Date 2019-09-10.19:10:54.811>
actor = 'Ronan.Lamy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-09-10.19:10:54.811>
creator = 'Ronan.Lamy'
dependencies = []
files = []
hgrepos = []
issue_num = 38095
keywords = []
message_count = 1.0
messages = ['351738']
nosy_count = 1.0
nosy_names = ['Ronan.Lamy']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38095'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9']