Operating System Experiment 5 Process Scheduling

Purpose:

The implementation first serves FCFS, short job priority SJF, and time slice rotation scheduling algorithm.

Lab content:

① Implement the FCFS algorithm: schedule several processes in the order of arrival time.

② Implement the SJF algorithm: select the minimum time for the process to run according to the current time.

③ Implement the time slice Rotation Algorithm: first, determine the size of the time slice and add it to the queue based on the arrival time of the process. Each time a time slice size is allocated, if it is not completed to participate in the next competition, this process is completed and the queue is exited when a time slice earlier than or equal to the time slice is required.

④ Calculate the average turnaround time and average weighted turnaround time of the system after each algorithm is scheduled.

Algorithm Implementation:

void FCFS(){inti;floatsumT = 0.0;floatsumW = 0.0;floatlast ;process[0].start = process[0].arrive;process[0].finish = process[0].start + process[0].service;last = process[0].finish;i = 1;while(i != N){if(process[i].arrive > last)last = process[i].arrive;process[i].start = last;process[i].finish = last + process[i].service;last += process[i].service;i++;}for(i = 0 ; i < N; i++){process[i].T = process[i].finish - process[i].arrive;process[i].W = process[i].T / (float)process[i].service;sumT += process[i].T;sumW += process[i].W;}FCFS_T = sumT / N;FCFS_W = sumW / N;}int getmin(float t){inti;intaddr = -1;floatmin=10000.0;for(i = 0 ; i < N ; i++){if(process[i].state == 0 && process[i].service < min && process[i].arrive <= t){addr = i;min = process[i].service;}}process[addr].finish = t + process[addr].service;return addr;}void SJF(){inti;floatsumT = 0.0;floatsumW = 0.0;process[0].finish = process[0].arrive + process[0].service;process[0].state  = 1;intaddr = 0;intsign = 0; floatlast = process[0].finish;while(sign != N-1){addr = getmin(last);if(addr == -1){last = process[getmin(1000)].arrive;continue;}process[addr].start = last;process[addr].state = 1;last = process[addr].finish;sign++;}for(i = 0 ; i < N; i++){process[i].T = process[i].finish - process[i].arrive;process[i].W = process[i].T / (float)process[i].service;sumT += process[i].T;sumW += process[i].W;}SJF_T = sumT / N;SJF_W = sumW / N;}void RR(){inti = 0;intj;intt = process[0].arrive;floatsumT = 0.0;floatsumW = 0.0;for(j = 0 ; j < N ; j++){process[j].state = 0;process[j].start = -1;process[j].left = process[j].service;}process[0].start = t;while(1){for(j = 0 ; j < N ; j++)if(process[(i+j)% N].state == 0 && t >= process[(i+j)% N].arrive)break;i = (i+j)% N;if( process[i].state == 1){break;}if(process[i].start == -1)process[i].start = t;for(j = 0 ; j < min(process[i].left,q) ; j++)cout <<process[i].name;if(process[i].left > q){t += q;process[i].left -= q;}else{t += process[i].left;process[i].left = 0;process[i].finish = t;process[i].state = 1;}i = (++i) %N;}for(i = 0 ; i < N ; i++){process[i].T = process[i].finish - process[i].arrive;process[i].W = process[i].T / (float)process[i].service;sumT += process[i].T;sumW += process[i].W;}RR_T = sumT / N;RR_W = sumW / N; }