thr_setprio() returns 0 if successful. When any of the following conditions is detected, thr_setprio() fails and returns the corresponding value.
ESRCH
Description:The value specified by tid does not refer to an existing thread.
EINVAL
Description:The value of priority is invalid for the scheduling policy of the specified thread.
EPERM
Description:The caller does not have the appropriate permission to set the priority to the value specified.