Common setup sequence for all user-callable interfaces.

def _get_candidate_names():
    """Common setup sequence for all user-callable interfaces."""

    global _name_sequence
    if _name_sequence is None:
        _once_lock.acquire()
        try:
            if _name_sequence is None:
                _name_sequence = _RandomNameSequence()
        finally:
            _once_lock.release()
    return _name_sequence