Semester 4 Operating System : Pre Emptive SJF java program / code

Given below is Java program for Pre Emptive SJF.

//Aim:To implement preemptive SJF scheduling //Program: import java.util.*; class PR { int bt; int at; PR() { bt=0; at=0; } PR(int x,int y) { bt=x; at=y; } } class PESJF { 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; } /* Assume that the none of the processes terminate before all the processes have arrived */ 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; for(i=0;i<n;++i) { System.out.println("Enter the burst time and arrival time of a process"); bt=scr.nextInt(); at=scr.nextInt(); p[i]=new PR(bt,at); } 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 time=p[n-1].at; int tt[]=new int[n]; int wt[]=new int[n]; int b[]=new int[n]; for(i=0;i<n;++i) { System.out.println("Process "+(i+1)+" Burst time= "+p[i].bt+" Arrival time= "+p[i].at); b[i]=p[i].bt; } int mat=p[n-1].at; int pn=0; i=0; j=0; p1:while(j<mat) { while(j<p[i+1].at) { if(p[pn].bt>0) { p[pn].bt--; ++j; } else { System.out.println("Process "+(pn+1)+" executed.Turn around time= "+b[pn]+" Wait time=0"); ++i; for(int y=0;y<i;++y) { for(int z=y;z<i-1;++z) { if((p[y].bt<p[z].bt)&&p[y].bt>0) pn=y; } } continue p1; }} if(i<n-1) if(p[i+1].bt<p[pn].bt) pn=(i+1); ++i; } System.out.println("After arrival of all processes"); for(int g=0;g<n;++g) System.out.println("Burst time of process "+(g+1)+"left = "+ p[g].bt+" "); System.out.println("Time elapsed= "+i); time=i; int k=0; int min=0; do { min=0; if(p[0].bt==0) for(i=0;i<n;++i) { if(p[i].bt!=0) { min=i; break; } } for(i=0;i<n;++i) { if((p[i].bt<p[min].bt)&&p[i].bt>0) min=i; } while(p[min].bt>0) { ++time; p[min].bt--; } tt[min]=(time-p[min].at); wt[min]=(tt[min]-b[min]); System.out.println("Process "+(min+1)+" executed.Turn around time= "+tt[min]+" Wait time= "+wt[min]); ++k; } while(sum(p,n)!=1); double att=0,awt=0; double s1=0,s2=0; 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 4 Enter the burst time and arrival time of a process 8 0 Enter the burst time and arrival time of a process 4 1 Enter the burst time and arrival time of a process 9 2 Enter the burst time and arrival time of a process 5 3 Process 1 Burst time= 8 Arrival time= 0 Process 2 Burst time= 4 Arrival time= 1 Process 3 Burst time= 9 Arrival time= 2 Process 4 Burst time= 5 Arrival time= 3 After arrival of all processes Burst time of process 1left = 7 Burst time of process 2left = 2 Burst time of process 3left = 9 Burst time of process 4left = 5 Time elapsed= 3 Process 2 executed.Turn around time= 4 Wait time= 0 Process 4 executed.Turn around time= 7 Wait time= 2 Process 1 executed.Turn around time= 17 Wait time= 9 Process 3 executed.Turn around time= 24 Wait time= 15 Average Turn around time= 13.0 Average wait time= 6.5 */