Sem 4 Operating System : Process scheduling Algorithm - Pre-emptive Priority Algorithm Java program / code

Given below is Java program for Pre-emptive Priority algorithm.

//Aim:To implement preemptive priority scheduling //Program: import java.util.*; class PR { public int bt; public int at; public int pt; public int pr; PR() { bt=0; at=0; pt=0; } PR(int x,int y,int z) { bt=x; at=y; pt=z; } void t(PR p2) { pr=p2.at-at; } } class PEP { static int sum(PR p[],int n) { int s=0; for(int i=0;i<n;++i) s+=p[i].bt; if(s==0) return 1; else return 0; } public static void main(String args[]) { PR p[]; Scanner scr=new Scanner(System.in); System.out.println("Enter the number of processes"); int n=scr.nextInt(); p=new PR[n]; int i=0,j=0; int bt,at,pt; for(i=0;i<n;++i) { System.out.println("Enter the burst time and arrival time & priority of a process"); bt=scr.nextInt(); at=scr.nextInt(); pt=scr.nextInt(); p[i]=new PR(bt,at,pt); } PR temp; // Sorting processes in increasing order of arrival time for(i=0;i<=n-2;++i) { for(j=i;j<=n-1;++j) { if(p[i].at>p[j].at) { temp=p[i]; p[i]=p[j]; p[j]=temp; } } } int tt[]=new int[n]; int wt[]=new int[n]; int b[]=new int[n]; for(i=0;i<n;++i) b[i]=p[i].bt; for(i=0;i<n;++i) { System.out.println("Process "+(i+1)+" Burst time= "+p[i].bt+" priority= "+p[i].pt+" Arrival time= "+p[i].at); } int time=0; int av; for(int k=0;k<n-1;++k) { p[k].t(p[k+1]); } System.out.println(); int t1; do { t1=0; av=0; for(i=0;i<n;++i) if(p[i].at<=time) ++av; int hp; int max=0; if(p[0].bt==0) { for(i=1;i<n;++i) if(p[i].bt!=0) { max=i;break; } } for(i=0;i<av;++i) { if((p[max].pt>p[i].pt) && p[i].bt>0) max=i; } hp=max; p[hp].bt-=1; ++time; if(p[hp].bt==0) tt[hp]=time; ++t1; } while(sum(p,n)!=1); double att=0,awt=0; double s1=0,s2=0; for(i=0;i<n;++i) tt[i]=tt[i]-p[i].at; System.out.println(); for(int h=0;h<n;++h) System.out.println("Turn around time of process "+(h+1)+" = "+tt[h]+" wait time = "+(tt[h]-b[h])); for(i=0;i<n;++i) wt[i]=tt[i]-b[i]; for(i=0;i<n;++i) { s1+=tt[i]; s2+=wt[i]; } att=s1/n; awt=s2/n; System.out.println("Average Turn around time= "+att+" Average wait time= "+awt); } } /* output Enter the number of processes 5 Enter the burst time and arrival time & priority of a process 10 0 3 Enter the burst time and arrival time & priority of a process 1 1 1 Enter the burst time and arrival time & priority of a process 2 2 3 Enter the burst time and arrival time & priority of a process 1 3 4 Enter the burst time and arrival time & priority of a process 5 4 2 Process 1 Burst time= 10 priority= 3 Arrival time= 0 Process 2 Burst time= 1 priority= 1 Arrival time= 1 Process 3 Burst time= 2 priority= 3 Arrival time= 2 Process 4 Burst time= 1 priority= 4 Arrival time= 3 Process 5 Burst time= 5 priority= 2 Arrival time= 4 Turn around time of process 1 = 16 wait time = 6 Turn around time of process 2 = 1 wait time = 0 Turn around time of process 3 = 16 wait time = 14 Turn around time of process 4 = 16 wait time = 15 Turn around time of process 5 = 5 wait time = 0 Average Turn around time= 10.8 Average wait time= 7.0 */