c program to demonstrate the concept of preemptive priority scheduling algorithm code example
Example 1: c program to implement non preemptive priority scheduling algorithm
#include<stdio.h>
int main()
{
int bt[20],p[20],wt[20],tat[20],pr[20],i,j,n,total=0,pos,temp,avg_wt,avg_tat;
printf("Enter Total Number of Process:");
scanf("%d",&n);
printf("\nEnter Burst Time and Priority\n");
for(i=0;i<n;i++)
{
printf("\nP[%d]\n",i+1);
printf("Burst Time:");
scanf("%d",&bt[i]);
printf("Priority:");
scanf("%d",&pr[i]);
p[i]=i+1;
}
for(i=0;i<n;i++)
{
pos=i;
for(j=i+1;j<n;j++)
{
if(pr[j]<pr[pos])
pos=j;
}
temp=pr[i];
pr[i]=pr[pos];
pr[pos]=temp;
temp=bt[i];
bt[i]=bt[pos];
bt[pos]=temp;
temp=p[i];
p[i]=p[pos];
p[pos]=temp;
}
wt[0]=0;
for(i=1;i<n;i++)
{
wt[i]=0;
for(j=0;j<i;j++)
wt[i]+=bt[j];
total+=wt[i];
}
avg_wt=total/n;
total=0;
printf("\nProcess\t Burst Time \tWaiting Time\tTurnaround Time");
for(i=0;i<n;i++)
{
tat[i]=bt[i]+wt[i];
total+=tat[i];
printf("\nP[%d]\t\t %d\t\t %d\t\t\t%d",p[i],bt[i],wt[i],tat[i]);
}
avg_tat=total/n;
printf("\n\nAverage Waiting Time=%d",avg_wt);
printf("\nAverage Turnaround Time=%d\n",avg_tat);
return 0;
}
Example 2: preemptive priority scheduling implementation in c
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <string.h>
using namespace std;
struct process {
int pid;
int arrival_time;
int burst_time;
int priority;
int start_time;
int completion_time;
int turnaround_time;
int waiting_time;
int response_time;
};
int main() {
int n;
struct process p[100];
float avg_turnaround_time;
float avg_waiting_time;
float avg_response_time;
float cpu_utilisation;
int total_turnaround_time = 0;
int total_waiting_time = 0;
int total_response_time = 0;
int total_idle_time = 0;
float throughput;
int burst_remaining[100];
int is_completed[100];
memset(is_completed,0,sizeof(is_completed));
cout << setprecision(2) << fixed;
cout<<"Enter the number of processes: ";
cin>>n;
for(int i = 0; i < n; i++) {
cout<<"Enter arrival time of process "<<i+1<<": ";
cin>>p[i].arrival_time;
cout<<"Enter burst time of process "<<i+1<<": ";
cin>>p[i].burst_time;
cout<<"Enter priority of the process "<<i+1<<": ";
cin>>p[i].priority;
p[i].pid = i+1;
burst_remaining[i] = p[i].burst_time;
cout<<endl;
}
int current_time = 0;
int completed = 0;
int prev = 0;
while(completed != n) {
int idx = -1;
int mx = -1;
for(int i = 0; i < n; i++) {
if(p[i].arrival_time <= current_time && is_completed[i] == 0) {
if(p[i].priority > mx) {
mx = p[i].priority;
idx = i;
}
if(p[i].priority == mx) {
if(p[i].arrival_time < p[idx].arrival_time) {
mx = p[i].priority;
idx = i;
}
}
}
}
if(idx != -1) {
if(burst_remaining[idx] == p[idx].burst_time) {
p[idx].start_time = current_time;
total_idle_time += p[idx].start_time - prev;
}
burst_remaining[idx] -= 1;
current_time++;
prev = current_time;
if(burst_remaining[idx] == 0) {
p[idx].completion_time = current_time;
p[idx].turnaround_time = p[idx].completion_time - p[idx].arrival_time;
p[idx].waiting_time = p[idx].turnaround_time - p[idx].burst_time;
p[idx].response_time = p[idx].start_time - p[idx].arrival_time;
total_turnaround_time += p[idx].turnaround_time;
total_waiting_time += p[idx].waiting_time;
total_response_time += p[idx].response_time;
is_completed[idx] = 1;
completed++;
}
}
else {
current_time++;
}
}
int min_arrival_time = 10000000;
int max_completion_time = -1;
for(int i = 0; i < n; i++) {
min_arrival_time = min(min_arrival_time,p[i].arrival_time);
max_completion_time = max(max_completion_time,p[i].completion_time);
}
avg_turnaround_time = (float) total_turnaround_time / n;
avg_waiting_time = (float) total_waiting_time / n;
avg_response_time = (float) total_response_time / n;
cpu_utilisation = ((max_completion_time - total_idle_time) / (float) max_completion_time )*100;
throughput = float(n) / (max_completion_time - min_arrival_time);
cout<<endl<<endl;
cout<<"#P\t"<<"AT\t"<<"BT\t"<<"PRI\t"<<"ST\t"<<"CT\t"<<"TAT\t"<<"WT\t"<<"RT\t"<<"\n"<<endl;
for(int i = 0; i < n; i++) {
cout<<p[i].pid<<"\t"<<p[i].arrival_time<<"\t"<<p[i].burst_time<<"\t"<<p[i].priority<<"\t"<<p[i].start_time<<"\t"<<p[i].completion_time<<"\t"<<p[i].turnaround_time<<"\t"<<p[i].waiting_time<<"\t"<<p[i].response_time<<"\t"<<"\n"<<endl;
}
cout<<"Average Turnaround Time = "<<avg_turnaround_time<<endl;
cout<<"Average Waiting Time = "<<avg_waiting_time<<endl;
cout<<"Average Response Time = "<<avg_response_time<<endl;
cout<<"CPU Utilization = "<<cpu_utilisation<<"%"<<endl;
cout<<"Throughput = "<<throughput<<" process/unit time"<<endl;
}
}