The function int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy); sets the schedpolicy attribute in the 'attr' argument. The supported values of 'policy' include SCHED_FIFO, SCHED_RR, and SCHED_OTHER. When threads executing with the scheduling policy are waiting on a mutex, they shall acquire the mutex in priority order when the mutex is unlocked. If success, it returns zero. if fail, an error number shall be returned to indicate the error. The pthread_attr_setschedpolicy() function may fail if: [EINVAL] The value of policy is invalid. [ENOTSUP] An attempt to set the attribute to an unsupported value. Shall not return an error code of [EINTR]