On successful completion, pthread_mutex_getprioceiling() returns 0. Any other return value indicates that an error occurred.
If any of the following conditions occurs, pthread_mutexatt_getprioceiling() fails and returns the corresponding value.
The option _POSIX_THREAD_PRIO_PROTECT is not defined and the implementation does not support the function.
If any of the following conditions occurs, pthread_mutex_getprioceiling() might fail and return the corresponding value.