pthread_setschedprio() returns zero after completing successfully. Any other return value indicates that an error occurred. When the following condition occurs, the function fails and returns the corresponding value.
EINVAL
Description:The value of prio is invalid for the scheduling policy of the specified thread.
ENOTSUP
Description:An attempt was made to set the priority to an unsupported value.
EPERM
Description:The caller does not have the appropriate permission to set the scheduling priority of the specified thread.
ESRCH
Description:The value specified by tid does not refer to an existing thread.