Round Robin Scheduling Program in C

Here you will learn Round Robin Scheduling Algorithm using gantt chart and the source code of Round Robin Scheduling Program in C language.

Round Robin Scheduling

Round Robin in operating system is a type of preemptive scheduling algorithm used in computer multitasking systems. It assigns CPU time in a cyclic way to each process in a queue. This ensures that every process is allocated a fair share of CPU time, and prevents the starvation of any process. It is particularly useful in time-sharing systems, where multiple users have access to the same computer.

Difference between FCFS and Round Robin

*First Come First Served (FCFS)*	*Round Robin (RR)*
♦ First Come First Served (FCFS) scheduling algorithm is a scheduling algorithm where processes are scheduled according to their arrival time.	♦ Round Robin scheduling algorithm is a scheduling algorithm where processes are scheduled in a round-robin fashion.
♦ The process that arrives first will be scheduled first.	♦ Each process is given a fixed time slice (quantum), and once a process has used up its quantum. It is preempted and moved to the bottom of the ready queue.
♦ First Come First Served (FCFS) is non-preemptive scheduling algorithm.	♦ Round Robin(RR) is the preemptive and added to the end of the ready queue.

Working of Round Robin

Process Burst time

P1 48

P2 16

P3 62

P4 28

Process P1 will be allocated for 20 time unit after then pre-empted to next process. This process will be continue till all process execution done.

Waiting time of process = (start time-arrival time)+(new time -old finish time)

Step 1. Waiting time P1 = (0-0)+(76-20)+(124-96) = 84.

Step 2. Waiting time P2 = (20-0) = 20.

Step 3. Waiting time P3 = (36-0)+(96-56)+(132-116) = 92.

Step 4. Waiting time P4 = (56-0)+(116-76) = 96.

Step 5. Average Waiting time = (292)/4 = 73.

Waiting Time :

Waiting Time = Turn around time – Burst Time.

Turn Around Time :

Turn Around Time = Completion Time – Arrival Time.

Turn around time = Burst time + Waiting time.

Example of Round Robin Scheduling Program in C

//Round Robin Scheduling Program in C

#include<stdio.h>

int main()

{

int n,i,j,temp1,temp2;

printf("Input no. of processes: \n");

scanf("%d",&n);

int bt[n],at[n],p[n],wt[n],tat[n],ct[n];

float avgwt=0,avgtat=0;

printf("Input arrival time and burst time of process : \n");

for(i=0;i<n;i++)

{

printf("Process %d: \n",i+1);

scanf("%d",&at[i]);

scanf("%d",&bt[i]);

p[i]=i+1;

}

// sort by arrival time

for(i=0;i<n;i++)

{

for(j=0;j<n;j++)

{

if(at[i]<at[j])

{

temp1=bt[j];

bt[j]=bt[i];

bt[i]=temp1;

temp1=at[j];

at[j]=at[i];

at[i]=temp1;

temp2=p[j];

p[j]=p[i];

p[i]=temp2;

}

//calculating completion time

for(i=0;i<n;i++)

{

if(i==0)

{

ct[i]=at[i]+bt[i];

}

else

{

if(at[i]>ct[i-1])

{

ct[i]=at[i]+bt[i];

}

else

{

ct[i]=ct[i-1]+bt[i];

}

tat[i]=ct[i]-at[i];

wt[i]=tat[i]-bt[i];

avgwt+=wt[i];

avgtat+=tat[i];

}

avgwt=avgwt/n;

avgtat=avgtat/n;

printf("\nProcess\tAT\tBT\tCT\tTAT\tWT\n");

for(i=0;i<n;i++)

{

printf("%d\t%d\t%d\t%d\t%d\t%d\n",p[i],at[i],bt[i],ct[i],tat[i],wt[i]);

}

printf("Average Waiting Time: %f\n",avgwt);

printf("Average Turn Around Time: %f\n",avgtat);

return 0;

}

Output

Read Also

FCFS scheduling program in C

Round Robin Scheduling Program in C