pthread_setschedparam() returns zero after completing successfully. Any other return value indicates that an error occurred. When either of the following conditions occurs, the pthread_setschedparam() function fails and returns the corresponding value.
EINVAL
Description:The value of the attribute being set is not valid.
EPERM
Description:The caller does not have the appropriate permission to set either the scheduling parameters or the scheduling policy of the specified thread.
ESRCH
Description:The value specified by tid does not refer to an existing thread.