By the way, I'm not sure about the error handling code path:

    for handler in _at_fork_reinit_lock_weakset:
        try:
            handler.createLock()
        except Exception as err:
            # Similar to what PyErr_WriteUnraisable does.
            print("Ignoring exception from logging atfork", instance,
                  "._reinit_lock() method:", err, file=sys.stderr)

Is it really a good idea to ignore such error?

By the way, there is an obvious typo: "instance" name doesn't exist, it should be "handler" :-)