On successful completion, pthread_mutexattr_getrobust_np() returns 0. Any other returned value indicates that an error occurred.
If any of the following conditions occurs, pthread_mutexattr_getrobust_np() fails and returns the corresponding value.
The option _POSIX_THREAD_PRIO__INHERIT is not defined or the implementation does not support pthread_mutexattr_getrobust_np().
The value specified by robustness is not supported.
pthread_mutexattr_getrobust_np() might fail if: