Question

Develop an algorithm and implement a Preemptive Priority scheduling algorithm using C++ and using bubble sorting .Arrival time, burst time and priority values.The code should also display:

(i) Gantt chart and determine the following:

(ii) Determine the Turnaround time(TAT), waiting time(WT) of each process

(iii) Determine the Average Waiting Time (AWT) and Average Turnaround Time (ATAT)

of all processes.

please write the comments

Answer 1

Preemptive Priority scheduling - each process has a priority associated with it and process with higher priority are executed first.

Implementing a Preemptive Priority scheduling algorithm using C++

#include<iostream>
#include<algorithm>
using namespace std;
struct node{
char pname;
int btime;
int atime;
int priority;
int restime=0;
int ctime=0;
int wtime=0;
}a[1000],b[1000],c[1000]; // declare 3 arrays
void insert(int n){
int i;
for(i=0;i<n;i++){ // for loop to get input from user
cin>>a[i].pname;
cin>>a[i].priority;
cin>>a[i].atime;
cin>>a[i].btime;
a[i].wtime=-a[i].atime+1;
}
}
bool btimeSort(node a,node b){
return a.btime < b.btime;
}
bool atimeSort(node a,node b){
return a.atime < b.atime;
}
bool prioritySort(node a,node b){ // sorting according to priority
return a.priority < b.priority;
}
int k=0,f=0,r=0;
void disp(int nop,int qt){
int n=nop,q;
sort(a,a+n,atimeSort);
int ttime=0,i;
int j,tArray[n];
int alltime=0;
bool moveLast=false;
for(i=0;i<n;i++){
alltime+=a[i].btime;
}
alltime+=a[0].atime;
for(i=0;ttime<=alltime;){
j=i;
while(a[j].atime<=ttime&&j!=n){
b[r]=a[j];
j++;
r++;
}
if(r==f){
c[k].pname='i';
c[k].btime=a[j].atime-ttime;
c[k].atime=ttime;
ttime+=c[k].btime;
k++;
continue;
}
i=j;
if(moveLast==true){
sort(b+f,b+r,prioritySort);
// b[r]=b[f];
// f++;
// r++;
}
j=f;
if(b[j].btime>qt){
c[k]=b[j];
c[k].btime=qt;
k++;
b[j].btime=b[j].btime-qt;
ttime+=qt;
moveLast=true;
for(q=0;q<n;q++){
if(b[j].pname!=a[q].pname){
a[q].wtime+=qt;
}
}
}
else{
c[k]=b[j];
k++;
f++;
ttime+=b[j].btime;
moveLast=false;
for(q=0;q<n;q++){
if(b[j].pname!=a[q].pname){
a[q].wtime+=b[j].btime;
}
}
}
if(f==r&&i>=n)
break;
}
tArray[i]=ttime;
ttime+=a[i].btime;
for(i=0;i<k-1;i++){
if(c[i].pname==c[i+1].pname){
c[i].btime+=c[i+1].btime;
for(j=i+1;j<k-1;j++)
c[j]=c[j+1];
k--;
i--;
}
}
  
int rtime=0;
for(j=0;j<n;j++){
rtime=0;
for(i=0;i<k;i++){
if(c[i].pname==a[j].pname){
a[j].restime=rtime;
break;
}
rtime+=c[i].btime;
}
}
float averageWaitingTime=0;
float averageResponseTime=0;
float averageTAT=0;
  
cout<<"\nGantt Chart\n"; // draw Gantt chart
rtime=0;
for (i=0; i<k; i++){
if(i!=k)
cout<<"| "<<'P'<< c[i].pname << " ";
rtime+=c[i].btime;
for(j=0;j<n;j++){
if(a[j].pname==c[i].pname)
a[j].ctime=rtime;
}
}
cout<<"\n";
rtime=0;
for (i=0; i<k+1; i++){
cout << rtime << "\t";
tArray[i]=rtime;
rtime+=c[i].btime;
}
cout<<"\n";
cout<<"\n";
cout<<"P.Name Priority AT\tBT\tCT\tTAT\tWT\tRT\n"; // draw table with all information
for (i=0; i<nop&&a[i].pname!='i'; i++){
if(a[i].pname=='\0')
break;
cout <<'P'<< a[i].pname << "\t";
cout << a[i].priority << "\t";
cout << a[i].atime << "\t";
cout << a[i].btime << "\t";
cout << a[i].ctime << "\t";
cout << a[i].wtime+a[i].ctime-rtime+a[i].btime << "\t";
averageTAT+=a[i].wtime+a[i].ctime-rtime+a[i].btime;
cout << a[i].wtime+a[i].ctime-rtime << "\t";
averageWaitingTime+=a[i].wtime+a[i].ctime-rtime;
cout << a[i].restime-a[i].atime << "\t";

cout <<"\n";
}

// calculating average waiting time and turn around time

cout<<"Average Waiting time: "<<(float)averageWaitingTime/(float)n<<endl;
cout<<"Average TA time: "<<(float)averageTAT/(float)n<<endl;
}
int main(){
int nop,choice,i,qt;
cout<<"Enter number of processes\n";
cin>>nop;
cout<<"Enter process, priority, AT, BT\n";
insert(nop);
disp(nop,1);
return 0;
}

Note - As per the policy answering only first part