| /*request_list is a list of requests ordered by SCAN order. |
| schedule_list is a list of schedules that have a sequence of requests. |
| group_list is a list of groups that consist of adjacent best-effort requests. |
| is a schedule with the minimum seek time.*/ |
| procedure ADD_REQUEST(request R) |
| /* insert R into request_list by SCAN order. */ |
| for each request in request_list |
| if (.track_num > .track_num) then |
| insert_request(); /* insert request R in front of . */ |
| break; |
| end if |
| end for |
| /* group adjacent best-effort requests. */ |
| GROUP_REQUESTS(); |
| /*expand existing schedules by inserting . */ |
| EXPAND_SCHEDULES(); |
| /* remove schedules whose seek time is larger than that of |
| by a disk’s full sweep time, . */ |
| for each schedule in schedule_list |
| if (.seektime − .seektime > ) then |
| remove_schedule(, schedule_list); /* remove from schedule_list*/ |
| end if |
| end for |
| end procedure |
| procedure GROUP_REQUESTS(request ) |
| if (.type = real-time) then |
| for each group in group_list |
| /* if is located in , split the into two groups */ |
| if (.start_track_num < .track_num and .track_num < .end_track_num) then |
| split_group (, ); |
| return; |
| end if |
| end for |
| else /*R.type is best-effort. */ |
| /* and are left and right neighbour requests of , respectively, |
| and is a threshold for grouping. */ |
| if (.type = best-effort and .type = best-effort) then |
| if (.track_num − .track_num < ) then |
| insert_into_group(, ); /* add to the group including both |
| and . */ |
| return; |
| else if (.track_num − .track_num < and .track_num −.track_num < ) then |
| merge_groups(, ); /* merge group including and group |
| including . */ |
| return; |
| else if (.track_num − .track_num < ) then |
| insert_into_group (, ); /* add to the group including . */ |
| return; |
| else if (.track_num − .track_num < ) then |
| insert_into_group (, ); /* add to the group including . */ |
| return; |
| end if |
| else if (.type = best-effort and .type = real-time) then |
| if (.track_num − .track_num < ) then |
| insert_into_group (, ); /* add to the group including . */ |
| return; |
| end if |
| else if (.type = real-time and .type = best-effort) then |
| if (.track_num − .track_num < ) then |
| insert_into_group (, ); /* add to the group including . */ |
| return; |
| end if |
| else |
| create_group (); /* creates a new group including . */ |
| end if |
| end if |
| end procedure |
| procedure EXPAND_SCHEDULES(request ) |
| old_schedule_list ←schedule_list; |
| for each schedule in old_schedule_list |
| remove_schedule (, old_schedule_list); /* remove from old_schedule_list. */ |
| for each position in request sequences of |
| ← a new schedule created by inserting into position . |
| deadline_missed ← FALSE; |
| temp ← 0; |
| for each request in |
| temp + = .servicetime; |
| if (.deadline < temp) then |
| deadline_missed ← TRUE; |
| break; |
| end if |
| end for |
| if (deadline_missed = FALSE) then |
| insert_schedule (, new_schedule_list); /* insert into |
| new_schedule_list. */ |
| if (.seektime < .seektime) then |
| ← ; |
| end if |
| end if |
| end for |
| end for |
| schedule_list ←new_schedule_list; |
| end procedure |
