pthread_mutex_t는 지금까지는 spin_lock이 아닌 blocking으로 구현되어 있는 게 맞나요?

Examples of possible additional mutex attributes that have been discussed are spin_only, limited_spin, no_spin, recursive, and metered. (To explain what the latter attributes might mean: recursive mutexes would allow for multiple re-locking by the current owner; metered mutexes would transparently keep records of queue length, wait time, and so on.) Since there is not yet wide agreement on the usefulness of these resulting from shared implementation and usage experience, they are not yet specified in this volume of IEEE Std 1003.1-2001. Mutex attributes objects, however, make it possible to test out these concepts for possible standardization at a later time.

위는 die.net에의 http://www.die.net/doc/linux/man/man3/pthread_mutexattr_init.3.html 페이지에서 발취한 것입니다. 뮤텍스 속성 객체를 이용해서 뮤텍스를 spin_lock 혹은 blocking으로 구현 할 수 있는 것 같은데요~ 현재까지는 blocking 모델로 구현되어 있는 게 맞나요?