oslo.service fails with python3.9 due to Semaphore() not implementing _at_fork_reinit

oslo.service fails with python3.9 due to Semaphore() not implementing _at_fork_reinit

when testing oslo.service, it fails with AttributeErrors in python3.9, leading me to believe that oslo.concurrency is not compatible with python3.9 and i'm not sure how to fix it.

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-hirsute/hirsute/amd64/p/python-oslo.service/20201116_120433_0b2e5@/log.gz

{0} oslo_service.tests.test_periodic.PeriodicTasksTestCase.test_called_correct [0.008885s] ... ok
   ERROR [oslo_service.periodic_task] Error during AService.crashit
Traceback (most recent call last):
  File "/tmp/autopkgtest.yxXbpd/build.9dR/src/oslo_service/periodic_task.py", line 216, in run_periodic_tasks
    task(self, context)
  File "/tmp/autopkgtest.yxXbpd/build.9dR/src/oslo_service/tests/test_periodic.py", line 54, in crashit
    raise AnException('urg')
oslo_service.tests.test_periodic.AnException: urg
   ERROR [oslo_service.periodic_task] Error during AService.crashit
Traceback (most recent call last):
  File "/tmp/autopkgtest.yxXbpd/build.9dR/src/oslo_service/periodic_task.py", line 216, in run_periodic_tasks
    task(self, context)
  File "/tmp/autopkgtest.yxXbpd/build.9dR/src/oslo_service/tests/test_periodic.py", line 54, in crashit
    raise AnException('urg')
oslo_service.tests.test_periodic.AnException: urg
{0} oslo_service.tests.test_periodic.PeriodicTasksTestCase.test_called_thrice [0.005251s] ... ok
{0} oslo_service.tests.test_periodic.PeriodicTasksTestCase.test_name [0.002083s] ... ok
{0} oslo_service.tests.test_periodic.PeriodicTasksTestCase.test_raises [0.002519s] ... ok
Exception ignored in: <function _after_fork at 0x7f4da9878790>
Traceback (most recent call last):
  File "/usr/lib/python3.9/threading.py", line 1486, in _after_fork
    thread._reset_internal_locks(True)
  File "/usr/lib/python3.9/threading.py", line 827, in _reset_internal_locks
    self._started._at_fork_reinit()
  File "/usr/lib/python3.9/threading.py", line 527, in _at_fork_reinit
    self._cond._at_fork_reinit()
  File "/usr/lib/python3.9/threading.py", line 253, in _at_fork_reinit
    self._lock._at_fork_reinit()
AttributeError: 'Semaphore' object has no attribute '_at_fork_reinit'
Exception ignored in: <function _after_at_fork_child_reinit_locks at 0x7f4da93150d0>
Traceback (most recent call last):
  File "/usr/lib/python3.9/logging/__init__.py", line 251, in _after_at_fork_child_reinit_locks
    handler._at_fork_reinit()
  File "/usr/lib/python3.9/logging/__init__.py", line 890, in _at_fork_reinit
    self.lock._at_fork_reinit()
  File "/usr/lib/python3.9/threading.py", line 126, in _at_fork_reinit
    self._block._at_fork_reinit()
AttributeError: 'Semaphore' object has no attribute '_at_fork_reinit'
Exception ignored in: <function _after_fork at 0x7f4da8a203a0>
Traceback (most recent call last):
  File "/usr/lib/python3.9/threading.py", line 1492, in _after_fork
    thread._reset_internal_locks(False)
  File "/usr/lib/python3.9/threading.py", line 827, in _reset_internal_locks
    self._started._at_fork_reinit()
  File "/usr/lib/python3.9/threading.py", line 527, in _at_fork_reinit
    self._cond._at_fork_reinit()
  File "/usr/lib/python3.9/threading.py", line 253, in _at_fork_reinit
    self._lock._at_fork_reinit()