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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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