> thread = threading.Thread(target=loop._do_shutdown, args=(executor,future))

Correction:

> thread = threading.Thread(target=_do_shutdown, args=(loop, executor,future))

Also, it might make more sense to rename _do_shutdown() to _do_executor_shutdown() to give the function's name more context; renaming shouldn't be an issue since it's private. Plus, it was just added recently in 3.9, so there's even less backwards compatibility to be concerned with.