Round Robin:
A straightforward way to reduce the penalty that short jobs suffer with FCFS is to use preemption based on a clock. The simplest such policy is round robin. A clock interrupt is generated at periodic intervals. When the interrupt occurs, the currently running process is placed in the ready queue, and the next ready job is selected on a FCFS basis. This technique is also known as time slicing, because each process is given a slice of time before being preempted.
/* C program to implement Round Robin Scheduling */
#include <stdio.h>
#include <conio.h>
int initialise();
void sort();
void print();
void GC();
void WT(int,int,char);
int RR();
float averagewaitingtime();
float averageturnaroundtime();
int p[15],a[15],b[15],br[15],gc[30],n,time,k;
static int wt[15];
void main()
{
int k;
clrscr();
printf("Enter the time slice:");
fflush(stdin);
scanf("%d",&time);
n=initialise();
sort();
k=RR();
print();
printf("
Average Wating time = %.2fmsec. & Average Turnaround time= %.2fmsec.
",averagewaitingtime()/n,averageturnaroundtime()/n);
GC(k);
getch();
}
int RR()
{
int i,flag,left,k=0;
do
{
flag=1;
for(i=0;i<n;i++)
{
if ( br[i]==0 || (a[i] > (k*time)))
continue;
if(br[i] <= time)
{
left=br[i];
gc[k++]=p[i];
br[i]=0;
WT(i,left,l);
}
else
{
gc[k++]=p[i];
br[i]-=time;
WT(i,time,g);
}
}
for(i=0;i<n;i++)
if(br[i]!=0)
flag=0;
}while(!flag);
return k;
}
void WT(int i,int add,char ch)
{
int j;
if ( ch == l )
{
for(j=0;j<n;j++)
if( j!=i && br[j]!=0 )
wt[j]+=add;
}
if ( ch == g )
{
for(j=0;j<n;j++)
if ( j!=i && br[j]!=0 )
wt[j]+=add;
}
}
void print()
{
int i;
printf("
| Process | Arrival time | Burst_Time | Waiting_Time | T_arnd_Time |
");
printf(" -------------------------------------------------------------------
");
for(i=0;i<n;i++)
printf(" |%4d |%8d |%6d |%8d |%6d |
",p[i],a[i],b[i],wt[i],b[i]+wt[i]);
printf(" --------------------------------------------------------------------
");
}
void GC(int g)
{
int i;
printf("
AND THE G.C IS :::
");
for(i=0;i<g;i++)
printf("------");
printf("
");
for(i=0;i<g;i++)
{
printf("| %d ",gc[i]);
if(i==g-1)
printf("|");
}
printf("
");
for(i=0;i<g;i++)
printf("------");
printf("
");
}
void sort()
{
int i,n,t,j;
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
if(a[i] > a[j])
{
t=p[i];
p[i]=p[j];
p[j]=t;
t=a[i];
a[i]=a[j];
a[j]=t;
t=b[i];
b[i]=b[j];
b[j]=t;
t=br[i];
br[i]=br[j];
br[j]=t;
}
}
}
}
int initialise()
{
FILE *fp;
int i=0,n1,n2,n3;
fp=fopen("sjf.txt","r");
while(fscanf(fp,"%d%d%d",&n1,&n2,&n3)!=EOF)
{
p[i]=n1;
a[i]=n2;
br[i]=b[i++]=n3;
}
fclose(fp);
return i;
}
float averagewaitingtime()
{
float sum=0;
int i;
for(i=0;i<n;i++)
sum+=wt[i];
return sum;
}
float averageturnaroundtime()
{
float sum=0;
int i;
for(i=0;i<n;i++)
sum+=(wt[i]+b[i]);
return sum;
}
Input File:
1 0 3
2 1 3
3 2 2
//Output Of the above program:-
A straightforward way to reduce the penalty that short jobs suffer with FCFS is to use preemption based on a clock. The simplest such policy is round robin. A clock interrupt is generated at periodic intervals. When the interrupt occurs, the currently running process is placed in the ready queue, and the next ready job is selected on a FCFS basis. This technique is also known as time slicing, because each process is given a slice of time before being preempted.
/* C program to implement Round Robin Scheduling */
#include <stdio.h>
#include <conio.h>
int initialise();
void sort();
void print();
void GC();
void WT(int,int,char);
int RR();
float averagewaitingtime();
float averageturnaroundtime();
int p[15],a[15],b[15],br[15],gc[30],n,time,k;
static int wt[15];
void main()
{
int k;
clrscr();
printf("Enter the time slice:");
fflush(stdin);
scanf("%d",&time);
n=initialise();
sort();
k=RR();
print();
printf("
Average Wating time = %.2fmsec. & Average Turnaround time= %.2fmsec.
",averagewaitingtime()/n,averageturnaroundtime()/n);
GC(k);
getch();
}
int RR()
{
int i,flag,left,k=0;
do
{
flag=1;
for(i=0;i<n;i++)
{
if ( br[i]==0 || (a[i] > (k*time)))
continue;
if(br[i] <= time)
{
left=br[i];
gc[k++]=p[i];
br[i]=0;
WT(i,left,l);
}
else
{
gc[k++]=p[i];
br[i]-=time;
WT(i,time,g);
}
}
for(i=0;i<n;i++)
if(br[i]!=0)
flag=0;
}while(!flag);
return k;
}
void WT(int i,int add,char ch)
{
int j;
if ( ch == l )
{
for(j=0;j<n;j++)
if( j!=i && br[j]!=0 )
wt[j]+=add;
}
if ( ch == g )
{
for(j=0;j<n;j++)
if ( j!=i && br[j]!=0 )
wt[j]+=add;
}
}
void print()
{
int i;
printf("
| Process | Arrival time | Burst_Time | Waiting_Time | T_arnd_Time |
");
printf(" -------------------------------------------------------------------
");
for(i=0;i<n;i++)
printf(" |%4d |%8d |%6d |%8d |%6d |
",p[i],a[i],b[i],wt[i],b[i]+wt[i]);
printf(" --------------------------------------------------------------------
");
}
void GC(int g)
{
int i;
printf("
AND THE G.C IS :::
");
for(i=0;i<g;i++)
printf("------");
printf("
");
for(i=0;i<g;i++)
{
printf("| %d ",gc[i]);
if(i==g-1)
printf("|");
}
printf("
");
for(i=0;i<g;i++)
printf("------");
printf("
");
}
void sort()
{
int i,n,t,j;
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
if(a[i] > a[j])
{
t=p[i];
p[i]=p[j];
p[j]=t;
t=a[i];
a[i]=a[j];
a[j]=t;
t=b[i];
b[i]=b[j];
b[j]=t;
t=br[i];
br[i]=br[j];
br[j]=t;
}
}
}
}
int initialise()
{
FILE *fp;
int i=0,n1,n2,n3;
fp=fopen("sjf.txt","r");
while(fscanf(fp,"%d%d%d",&n1,&n2,&n3)!=EOF)
{
p[i]=n1;
a[i]=n2;
br[i]=b[i++]=n3;
}
fclose(fp);
return i;
}
float averagewaitingtime()
{
float sum=0;
int i;
for(i=0;i<n;i++)
sum+=wt[i];
return sum;
}
float averageturnaroundtime()
{
float sum=0;
int i;
for(i=0;i<n;i++)
sum+=(wt[i]+b[i]);
return sum;
}
Input File:
1 0 3
2 1 3
3 2 2
//Output Of the above program:-
