pthread_attr_setschedparam() returns zero after completing successfully. Any other return value indicates that an error occurred. If the following conditions occur, the function fails and returns the corresponding value.
EINVAL
Description:The value of param is NULL or tattr is invalid.
You can manage pthreads priority in either of two ways:
You can set the priority attribute before creating a child thread
You can change the priority of the parent thread and then change the priority back