Round Robin is a CPU scheduling algorithm where each process is cyclically assigned a fixed time slot. It is the preemptive version of the First come First Serve CPU Scheduling algorithm.
- Round Robin CPU Algorithm generally focuses on Time Sharing technique.
- The period of time for which a process or job is allowed to run in a pre-emptive method is called time quantum.
- Each process or job present in the ready queue is assigned the CPU for that time quantum, if the execution of the process is completed during that time then the process will end else the process will go back to the waiting table and wait for its next turn to complete the execution.
Characteristics of Round Robin CPU Scheduling Algorithm
- It is simple, easy to implement, and starvation-free as all processes get a fair share of CPU.
- One of the most commonly used techniques in CPU scheduling is a core.
- It is preemptive as processes are assigned CPU only for a fixed slice of time at most.
- The disadvantage of it is more overhead of context switching.
Advantages of Round Robin CPU Scheduling Algorithm
- There is fairness since every process gets an equal share of the CPU.
- The newly created process is added to the end of the ready queue.
- A round-robin scheduler generally employs time-sharing, giving each job a time slot or quantum.
- While performing a round-robin scheduling, a particular time quantum is allotted to different jobs.
- Each process get a chance to reschedule after a particular quantum time in this scheduling.
Disadvantages of Round Robin CPU Scheduling Algorithm
- There is Larger waiting time and Response time.
- There is Low throughput.
- There is Context Switches.
- Gantt chart seems to come too big (if quantum time is less for scheduling. For Example:1 ms for big scheduling.)
- Time consuming scheduling for small quantum.
Examples to show working of Round Robin Scheduling Algorithm
Example-1: Consider the following table of arrival time and burst time for four processes P1, P2, P3, and P4 and given Time Quantum = 2
Process | Burst Time | Arrival Time |
---|---|---|
P1 | 5 ms | 0 ms |
P2 | 4 ms | 1 ms |
P3 | 2 ms | 2 ms |
P4 | 1 ms | 4 ms |
The Round Robin CPU Scheduling Algorithm will work on the basis of steps as mentioned below:
At time = 0,
- The execution begins with process P1, which has burst time 5.
- Here, every process executes for 2 milliseconds (Time Quantum Period). P2 and P3 are still in the waiting queue.
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
0-2ms | P1 | 0ms | P2, P3 | P1 | 2ms | 5ms | 3ms |
At time = 2,
- The processes P1 and P3 arrives in the ready queue and P2 starts executing for TQ period
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
2-4ms | P1 | 0ms | P3, P1 | P2 | 0ms | 3ms | 3ms |
P2 | 1ms | 2ms | 4ms | 2ms |
At time = 4,
- The process P4 arrives in the ready queue,
- Then P3 executes for TQ period.
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
4-6ms | P1 | 0ms | P1, P4, P2 | P3 | 0ms | 3ms | 3ms |
P2 | 1ms | 0ms | 2ms | 2ms | |||
At time = 6,
- Process P3 completes its execution
- Process P1 starts executing for TQ period as it is next in the b.
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
6-8ms | P1 | 0ms | P4, P2 | P1 | 2ms | 3ms | 1ms |
P2 | 1ms | 0ms | 2ms | 2ms |
At time = 8,
- Process P4 starts executing, it will not execute for Time Quantum period as it has burst time = 1
- Hence, it will execute for only 1ms.
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
8-9ms | P1 | 0ms | P2, P1 | P4 | 0ms | 3ms | 1ms |
P2 | 1ms | 0ms | 2ms | 2ms | |||
1ms | 1ms | 0ms |
At time = 9,
- Process P4 completes its execution
- Process P2 starts executing for TQ period as it is next in the ready queue
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
9-11ms | P1 | 0ms | P1 | P2 | 0ms | 3ms | 1ms |
At time = 11,
- Process P2 completes its execution.
- Process P1 starts executing, it will execute for 1ms only
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
11-12ms |
At time = 12,
- Process P1 completes its execution.
- The overall execution of the processes will be as shown below:
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time |
Remaining Burst Time |
---|---|---|---|---|---|---|---|
0-2ms | P1 | 0ms | P2, P3 | P1 | 2ms | 5ms | 3ms |
2-4ms | P1 | 0ms | P3, P1 | P2 | 0ms | 3ms | 3ms |
P2 | 1ms | 2ms | 4ms | 2ms | |||
4-6ms | P1 | 0ms | P1, P4, P2 | P3 | 0ms | 3ms | 3ms |
P2 | 1ms | 0ms | 2ms | 2ms | |||
6-8ms | P1 | 0ms | P4, P2 | P1 | 2ms | 3ms | 1ms |
P2 | 1ms | 0ms | 2ms | 2ms | |||
8-9ms | P1 | 0ms | P2, P1 | P4 | 0ms | 3ms | 1ms |
P2 | 1ms | 0ms | 2ms | 2ms | |||
1ms | 1ms | 0ms | |||||
9-11ms | P1 | 0ms | P1 | P2 | 0ms | 3ms | 1ms |
11-12ms |
Gantt chart will be as following below:
How to compute below times in Round Robin using a program?
- Completion Time: Time at which process completes its execution.
- Turn Around Time: Time Difference between completion time and arrival time. Turn Around Time = Completion Time – Arrival Time
-
Waiting Time(W.T): Time Difference between turn around time and burst time.
Waiting Time = Turn Around Time – Burst Time
Now, lets calculate average waiting time and turn around time:
Processes | AT | BT | CT | TAT | WT |
---|---|---|---|---|---|
P1 | 0 | 5 | 12 | 12-0 = 12 | 12-5 = 7 |
P2 | 1 | 4 | 11 | 11-1 = 10 | 10-4 = 6 |
P3 | 2 | 2 | 6 | 6-2 = 4 | 4-2 = 2 |
P4 | 4 | 1 | 9 | 9-4 = 5 | 5-1 = 4 |
Now,
- Average Turn around time = (12 + 10 + 4 + 5)/4 = 31/4 = 7.7
- Average waiting time = (7 + 6 + 2 + 4)/4 = 19/4 = 4.7
Example 2: Consider the following table of arrival time and burst time for three processes P1, P2 and P3 and given Time Quantum = 2
Process | Burst Time | Arrival Time |
---|---|---|
P1 | 10 ms | 0 ms |
P2 | 5 ms | 0 ms |
P3 | 8 ms | 0 ms |
Similarly, Gantt chart for this example:
Now, lets calculate average waiting time and turn around time:
Processes | AT | BT | CT | TAT | WT |
---|---|---|---|---|---|
P1 | 0 | 10 | 23 | 23-0 = 23 | 23-10 = 13 |
P2 | 0 | 5 | 15 | 15-0 = 15 | 15-5 = 10 |
P3 | 0 | 8 | 21 | 21-0 = 21 | 21-8 = 13 |
Total Turn Around Time = 59 ms
So, Average Turn Around Time = 59/3 = 19.667 msAnd, Total Waiting Time = 36 ms
So, Average Waiting Time = 36/3 = 12.00 ms
Program for Round Robin Scheduling with arrival time as 0 for all processes
Steps to find waiting times of all processes
- Create an array rem_bt[] to keep track of remaining burst time of processes. This array is initially a copy of bt[] (burst times array)
- Create another array wt[] to store waiting times of processes. Initialize this array as 0.
- Initialize time : t = 0
- Keep traversing all the processes while they are not done. Do following for i’th process if it is not done yet.
- If rem_bt[i] > quantum
- t = t + quantum
- rem_bt[i] -= quantum;
- Else // Last cycle for this process
- t = t + rem_bt[i];
- wt[i] = t – bt[i]
- rem_bt[i] = 0; // This process is over
Once we have waiting times, we can compute turn around time tat[i] of a process as sum of waiting and burst times, i.e., wt[i] + bt[i].
Below is implementation of above steps.
// C++ program for implementation of RR scheduling #include<iostream> using namespace std;
// Function to find the waiting time for all // processes void findWaitingTime( int processes[], int n,
int bt[], int wt[], int quantum)
{ // Make a copy of burst times bt[] to store remaining
// burst times.
int rem_bt[n];
for ( int i = 0 ; i < n ; i++)
rem_bt[i] = bt[i];
int t = 0; // Current time
// Keep traversing processes in round robin manner
// until all of them are not done.
while (1)
{
bool done = true ;
// Traverse all processes one by one repeatedly
for ( int i = 0 ; i < n; i++)
{
// If burst time of a process is greater than 0
// then only need to process further
if (rem_bt[i] > 0)
{
done = false ; // There is a pending process
if (rem_bt[i] > quantum)
{
// Increase the value of t i.e. shows
// how much time a process has been processed
t += quantum;
// Decrease the burst_time of current process
// by quantum
rem_bt[i] -= quantum;
}
// If burst time is smaller than or equal to
// quantum. Last cycle for this process
else
{
// Increase the value of t i.e. shows
// how much time a process has been processed
t = t + rem_bt[i];
// Waiting time is current time minus time
// used by this process
wt[i] = t - bt[i];
// As the process gets fully executed
// make its remaining burst time = 0
rem_bt[i] = 0;
}
}
}
// If all processes are done
if (done == true )
break ;
}
} // Function to calculate turn around time void findTurnAroundTime( int processes[], int n,
int bt[], int wt[], int tat[])
{ // calculating turnaround time by adding
// bt[i] + wt[i]
for ( int i = 0; i < n ; i++)
tat[i] = bt[i] + wt[i];
} // Function to calculate average time void findavgTime( int processes[], int n, int bt[],
int quantum)
{ int wt[n], tat[n], total_wt = 0, total_tat = 0;
// Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt, quantum);
// Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
// Display processes along with all details
cout << "PN\t " << " \tBT "
<< " WT " << " \tTAT\n" ;
// Calculate total waiting time and total turn
// around time
for ( int i=0; i<n; i++)
{
total_wt = total_wt + wt[i];
total_tat = total_tat + tat[i];
cout << " " << i+1 << "\t\t" << bt[i] << "\t "
<< wt[i] << "\t\t " << tat[i] <<endl;
}
cout << "Average waiting time = "
<< ( float )total_wt / ( float )n;
cout << "\nAverage turn around time = "
<< ( float )total_tat / ( float )n;
} // Driver code int main()
{ // process id's
int processes[] = { 1, 2, 3};
int n = sizeof processes / sizeof processes[0];
// Burst time of all processes
int burst_time[] = {10, 5, 8};
// Time quantum
int quantum = 2;
findavgTime(processes, n, burst_time, quantum);
return 0;
} |
// Java program for implementation of RR scheduling public class GFG
{ // Method to find the waiting time for all
// processes
static void findWaitingTime( int processes[], int n,
int bt[], int wt[], int quantum)
{
// Make a copy of burst times bt[] to store remaining
// burst times.
int rem_bt[] = new int [n];
for ( int i = 0 ; i < n ; i++)
rem_bt[i] = bt[i];
int t = 0 ; // Current time
// Keep traversing processes in round robin manner
// until all of them are not done.
while ( true )
{
boolean done = true ;
// Traverse all processes one by one repeatedly
for ( int i = 0 ; i < n; i++)
{
// If burst time of a process is greater than 0
// then only need to process further
if (rem_bt[i] > 0 )
{
done = false ; // There is a pending process
if (rem_bt[i] > quantum)
{
// Increase the value of t i.e. shows
// how much time a process has been processed
t += quantum;
// Decrease the burst_time of current process
// by quantum
rem_bt[i] -= quantum;
}
// If burst time is smaller than or equal to
// quantum. Last cycle for this process
else
{
// Increase the value of t i.e. shows
// how much time a process has been processed
t = t + rem_bt[i];
// Waiting time is current time minus time
// used by this process
wt[i] = t - bt[i];
// As the process gets fully executed
// make its remaining burst time = 0
rem_bt[i] = 0 ;
}
}
}
// If all processes are done
if (done == true )
break ;
}
}
// Method to calculate turn around time
static void findTurnAroundTime( int processes[], int n,
int bt[], int wt[], int tat[])
{
// calculating turnaround time by adding
// bt[i] + wt[i]
for ( int i = 0 ; i < n ; i++)
tat[i] = bt[i] + wt[i];
}
// Method to calculate average time
static void findavgTime( int processes[], int n, int bt[],
int quantum)
{
int wt[] = new int [n], tat[] = new int [n];
int total_wt = 0 , total_tat = 0 ;
// Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt, quantum);
// Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
// Display processes along with all details
System.out.println( "PN " + " B " +
" WT " + " TAT" );
// Calculate total waiting time and total turn
// around time
for ( int i= 0 ; i<n; i++)
{
total_wt = total_wt + wt[i];
total_tat = total_tat + tat[i];
System.out.println( " " + (i+ 1 ) + "\t\t" + bt[i] + "\t " +
wt[i] + "\t\t " + tat[i]);
}
System.out.println( "Average waiting time = " +
( float )total_wt / ( float )n);
System.out.println( "Average turn around time = " +
( float )total_tat / ( float )n);
}
// Driver Method
public static void main(String[] args)
{
// process id's
int processes[] = { 1 , 2 , 3 };
int n = processes.length;
// Burst time of all processes
int burst_time[] = { 10 , 5 , 8 };
// Time quantum
int quantum = 2 ;
findavgTime(processes, n, burst_time, quantum);
}
} |
# Python3 program for implementation of # RR scheduling # Function to find the waiting time # for all processes def findWaitingTime(processes, n, bt,
wt, quantum):
rem_bt = [ 0 ] * n
# Copy the burst time into rt[]
for i in range (n):
rem_bt[i] = bt[i]
t = 0 # Current time
# Keep traversing processes in round
# robin manner until all of them are
# not done.
while ( 1 ):
done = True
# Traverse all processes one by
# one repeatedly
for i in range (n):
# If burst time of a process is greater
# than 0 then only need to process further
if (rem_bt[i] > 0 ) :
done = False # There is a pending process
if (rem_bt[i] > quantum) :
# Increase the value of t i.e. shows
# how much time a process has been processed
t + = quantum
# Decrease the burst_time of current
# process by quantum
rem_bt[i] - = quantum
# If burst time is smaller than or equal
# to quantum. Last cycle for this process
else :
# Increase the value of t i.e. shows
# how much time a process has been processed
t = t + rem_bt[i]
# Waiting time is current time minus
# time used by this process
wt[i] = t - bt[i]
# As the process gets fully executed
# make its remaining burst time = 0
rem_bt[i] = 0
# If all processes are done
if (done = = True ):
break
# Function to calculate turn around time def findTurnAroundTime(processes, n, bt, wt, tat):
# Calculating turnaround time
for i in range (n):
tat[i] = bt[i] + wt[i]
# Function to calculate average waiting # and turn-around times. def findavgTime(processes, n, bt, quantum):
wt = [ 0 ] * n
tat = [ 0 ] * n
# Function to find waiting time
# of all processes
findWaitingTime(processes, n, bt,
wt, quantum)
# Function to find turn around time
# for all processes
findTurnAroundTime(processes, n, bt,
wt, tat)
# Display processes along with all details
print ( "Processes Burst Time Waiting" ,
"Time Turn-Around Time" )
total_wt = 0
total_tat = 0
for i in range (n):
total_wt = total_wt + wt[i]
total_tat = total_tat + tat[i]
print ( " " , i + 1 , "\t\t" , bt[i],
"\t\t" , wt[i], "\t\t" , tat[i])
print ( "\nAverage waiting time = %.5f " % (total_wt / n) )
print ( "Average turn around time = %.5f " % (total_tat / n))
# Driver code if __name__ = = "__main__" :
# Process id's
proc = [ 1 , 2 , 3 ]
n = 3
# Burst time of all processes
burst_time = [ 10 , 5 , 8 ]
# Time quantum
quantum = 2 ;
findavgTime(proc, n, burst_time, quantum)
# This code is contributed by # Shubham Singh(SHUBHAMSINGH10) |
// C# program for implementation of RR // scheduling using System;
public class GFG {
// Method to find the waiting time
// for all processes
static void findWaitingTime( int []processes,
int n, int []bt, int []wt, int quantum)
{
// Make a copy of burst times bt[] to
// store remaining burst times.
int []rem_bt = new int [n];
for ( int i = 0 ; i < n ; i++)
rem_bt[i] = bt[i];
int t = 0; // Current time
// Keep traversing processes in round
// robin manner until all of them are
// not done.
while ( true )
{
bool done = true ;
// Traverse all processes one by
// one repeatedly
for ( int i = 0 ; i < n; i++)
{
// If burst time of a process
// is greater than 0 then only
// need to process further
if (rem_bt[i] > 0)
{
// There is a pending process
done = false ;
if (rem_bt[i] > quantum)
{
// Increase the value of t i.e.
// shows how much time a process
// has been processed
t += quantum;
// Decrease the burst_time of
// current process by quantum
rem_bt[i] -= quantum;
}
// If burst time is smaller than
// or equal to quantum. Last cycle
// for this process
else
{
// Increase the value of t i.e.
// shows how much time a process
// has been processed
t = t + rem_bt[i];
// Waiting time is current
// time minus time used by
// this process
wt[i] = t - bt[i];
// As the process gets fully
// executed make its remaining
// burst time = 0
rem_bt[i] = 0;
}
}
}
// If all processes are done
if (done == true )
break ;
}
}
// Method to calculate turn around time
static void findTurnAroundTime( int []processes,
int n, int []bt, int []wt, int []tat)
{
// calculating turnaround time by adding
// bt[i] + wt[i]
for ( int i = 0; i < n ; i++)
tat[i] = bt[i] + wt[i];
}
// Method to calculate average time
static void findavgTime( int []processes, int n,
int []bt, int quantum)
{
int []wt = new int [n];
int []tat = new int [n];
int total_wt = 0, total_tat = 0;
// Function to find waiting time of
// all processes
findWaitingTime(processes, n, bt, wt, quantum);
// Function to find turn around time
// for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
// Display processes along with
// all details
Console.WriteLine( "Processes " + " Burst time " +
" Waiting time " + " Turn around time" );
// Calculate total waiting time and total turn
// around time
for ( int i = 0; i < n; i++)
{
total_wt = total_wt + wt[i];
total_tat = total_tat + tat[i];
Console.WriteLine( " " + (i+1) + "\t\t" + bt[i]
+ "\t " + wt[i] + "\t\t " + tat[i]);
}
Console.WriteLine( "Average waiting time = " +
( float )total_wt / ( float )n);
Console.Write( "Average turn around time = " +
( float )total_tat / ( float )n);
}
// Driver Method
public static void Main()
{
// process id's
int []processes = { 1, 2, 3};
int n = processes.Length;
// Burst time of all processes
int []burst_time = {10, 5, 8};
// Time quantum
int quantum = 2;
findavgTime(processes, n, burst_time, quantum);
}
} // This code is contributed by nitin mittal. |
<script> // JavaScript program for implementation of RR scheduling
// Function to find the waiting time for all
// processes
const findWaitingTime = (processes, n, bt, wt, quantum) => {
// Make a copy of burst times bt[] to store remaining
// burst times.
let rem_bt = new Array(n).fill(0);
for (let i = 0; i < n; i++)
rem_bt[i] = bt[i];
let t = 0; // Current time
// Keep traversing processes in round robin manner
// until all of them are not done.
while (1) {
let done = true ;
// Traverse all processes one by one repeatedly
for (let i = 0; i < n; i++) {
// If burst time of a process is greater than 0
// then only need to process further
if (rem_bt[i] > 0) {
done = false ; // There is a pending process
if (rem_bt[i] > quantum) {
// Increase the value of t i.e. shows
// how much time a process has been processed
t += quantum;
// Decrease the burst_time of current process
// by quantum
rem_bt[i] -= quantum;
}
// If burst time is smaller than or equal to
// quantum. Last cycle for this process
else {
// Increase the value of t i.e. shows
// how much time a process has been processed
t = t + rem_bt[i];
// Waiting time is current time minus time
// used by this process
wt[i] = t - bt[i];
// As the process gets fully executed
// make its remaining burst time = 0
rem_bt[i] = 0;
}
}
}
// If all processes are done
if (done == true )
break ;
}
}
// Function to calculate turn around time
const findTurnAroundTime = (processes, n, bt, wt, tat) => {
// calculating turnaround time by adding
// bt[i] + wt[i]
for (let i = 0; i < n; i++)
tat[i] = bt[i] + wt[i];
}
// Function to calculate average time
const findavgTime = (processes, n, bt, quantum) => {
let wt = new Array(n).fill(0), tat = new Array(n).fill(0);
let total_wt = 0, total_tat = 0;
// Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt, quantum);
// Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
// Display processes along with all details
document.write(`Processes Burst time Waiting time Turn around time<br/>`);
// Calculate total waiting time and total turn
// around time
for (let i = 0; i < n; i++) {
total_wt = total_wt + wt[i];
total_tat = total_tat + tat[i];
document.write(`${i + 1} ${bt[i]} ${wt[i]} ${tat[i]}<br/>`);
}
document.write(`Average waiting time = ${total_wt / n}`);
document.write(`<br/>Average turn around time = ${total_tat / n}`);
}
// Driver code
// process id's
processes = [1, 2, 3];
let n = processes.length;
// Burst time of all processes
let burst_time = [10, 5, 8];
// Time quantum
let quantum = 2;
findavgTime(processes, n, burst_time, quantum);
// This code is contributed by rakeshsahni
</script> |
PN BT WT TAT 1 10 13 23 2 5 10 15 3 8 13 21 Average waiting time = 12 Average turn around time = 19.6667
Program for Round Robin Scheduling with arrival time as zero , different and same arrival times
#include <iostream> #include <climits> using namespace std;
struct Process {
int AT, BT, ST[20], WT, FT, TAT, pos;
}; int quant;
int main() {
int n, i, j;
// Taking Input
cout << "Enter the no. of processes: " ;
cin >> n;
Process p[n];
cout << "Enter the quantum: " << endl;
cin >> quant;
cout << "Enter the process numbers: " << endl;
for (i = 0; i < n; i++)
cin >> p[i].pos;
cout << "Enter the Arrival time of processes: " << endl;
for (i = 0; i < n; i++)
cin >> p[i].AT;
cout << "Enter the Burst time of processes: " << endl;
for (i = 0; i < n; i++)
cin >> p[i].BT;
// Declaring variables
int c = n, s[n][20];
float time = 0, mini = INT_MAX, b[n], a[n];
// Initializing burst and arrival time arrays
int index = -1;
for (i = 0; i < n; i++) {
b[i] = p[i].BT;
a[i] = p[i].AT;
for (j = 0; j < 20; j++) {
s[i][j] = -1;
}
}
int tot_wt, tot_tat;
tot_wt = 0;
tot_tat = 0;
bool flag = false ;
while (c != 0) {
mini = INT_MAX;
flag = false ;
for (i = 0; i < n; i++) {
float p = time + 0.1;
if (a[i] <= p && mini > a[i] && b[i] > 0) {
index = i;
mini = a[i];
flag = true ;
}
}
// if at =1 then loop gets out hence set flag to false
if (!flag) {
time ++;
continue ;
}
// calculating start time
j = 0;
while (s[index][j] != -1) {
j++;
}
if (s[index][j] == -1) {
s[index][j] = time ;
p[index].ST[j] = time ;
}
if (b[index] <= quant) {
time += b[index];
b[index] = 0;
} else {
time += quant;
b[index] -= quant;
}
if (b[index] > 0) {
a[index] = time + 0.1;
}
// calculating arrival, burst, final times
if (b[index] == 0) {
c--;
p[index].FT = time ;
p[index].WT = p[index].FT - p[index].AT - p[index].BT;
tot_wt += p[index].WT;
p[index].TAT = p[index].BT + p[index].WT;
tot_tat += p[index].TAT;
}
} // end of while loop
// Printing output
cout << "Process number " ;
cout << "Arrival time " ;
cout << "Burst time " ;
cout << "\tStart time" ;
j = 0;
while (j != 10) {
j += 1;
cout << " " ;
}
cout << "\t\tFinal time" ;
cout << "\tWait Time " ;
cout << "\tTurnAround Time" << endl;
for (i = 0; i < n; i++) {
cout << p[i].pos << "\t\t" ;
cout << p[i].AT << "\t\t" ;
cout << p[i].BT << "\t" ;
j = 0;
int v = 0;
while (s[i][j] != -1) {
cout << p[i].ST[j] << " " ;
j++;
v += 3;
}
while (v != 40) {
cout << " " ;
v += 1;
}
cout << p[i].FT << "\t\t" ;
cout << p[i].WT << "\t\t" ;
cout << p[i].TAT << endl;
}
// Calculating average wait time and turnaround time
double avg_wt, avg_tat;
avg_wt = tot_wt / static_cast < double >(n);
avg_tat = tot_tat / static_cast < double >(n);
// Printing average wait time and turnaround time
cout << "The average wait time is: " << avg_wt << endl;
cout << "The average TurnAround time is: " << avg_tat << endl;
return 0;
} |
#include<stdio.h> #include<limits.h> #include<stdbool.h> struct P{
int AT,BT,ST[20],WT,FT,TAT,pos;
}; int quant;
int main(){
int n,i,j;
// Taking Input printf ( "Enter the no. of processes :" );
scanf ( "%d" ,&n);
struct P p[n];
printf ( "Enter the quantum \n" );
scanf ( "%d" ,&quant);
printf ( "Enter the process numbers \n" );
for (i=0;i<n;i++)
scanf ( "%d" ,&(p[i].pos));
printf ( "Enter the Arrival time of processes \n" );
for (i=0;i<n;i++)
scanf ( "%d" ,&(p[i].AT));
printf ( "Enter the Burst time of processes \n" );
for (i=0;i<n;i++)
scanf ( "%d" ,&(p[i].BT));
// Declaring variables int c=n,s[n][20];
float time =0,mini=INT_MAX,b[n],a[n];
// Initializing burst and arrival time arrays int index=-1;
for (i=0;i<n;i++){
b[i]=p[i].BT;
a[i]=p[i].AT;
for (j=0;j<20;j++){
s[i][j]=-1;
}
} int tot_wt,tot_tat;
tot_wt=0; tot_tat=0; bool flag= false ;
while (c!=0){
mini=INT_MAX; flag= false ;
for (i=0;i<n;i++){
float p= time +0.1;
if (a[i]<=p && mini>a[i] && b[i]>0){
index=i;
mini=a[i];
flag= true ;
}
} // if at =1 then loop gets out hence set flag to false if (!flag){
time ++;
continue ;
} //calculating start time j=0; while (s[index][j]!=-1){
j++; } if (s[index][j]==-1){
s[index][j]= time ;
p[index].ST[j]= time ;
} if (b[index]<=quant){
time +=b[index];
b[index]=0; } else {
time +=quant;
b[index]-=quant; } if (b[index]>0){
a[index]= time +0.1;
} // calculating arrival,burst,final times if (b[index]==0){
c--; p[index].FT= time ;
p[index].WT=p[index].FT-p[index].AT-p[index].BT; tot_wt+=p[index].WT; p[index].TAT=p[index].BT+p[index].WT; tot_tat+=p[index].TAT; } } // end of while loop
// Printing output printf ( "Process number " );
printf ( "Arrival time " );
printf ( "Burst time " );
printf ( "\tStart time" );
j=0; while (j!=10){
j+=1; printf ( " " );
} printf ( "\t\tFinal time" );
printf ( "\tWait Time " );
printf ( "\tTurnAround Time \n" );
for (i=0;i<n;i++){
printf ( "%d \t\t" ,p[i].pos);
printf ( "%d \t\t" ,p[i].AT);
printf ( "%d \t" ,p[i].BT);
j=0; int v=0;
while (s[i][j]!=-1){
printf ( "%d " ,p[i].ST[j]);
j++; v+=3; } while (v!=40){
printf ( " " );
v+=1; } printf ( "%d \t\t" ,p[i].FT);
printf ( "%d \t\t" ,p[i].WT);
printf ( "%d \n" ,p[i].TAT);
} //Calculating average wait time and turnaround time double avg_wt,avg_tat;
avg_wt=tot_wt/( float )n;
avg_tat=tot_tat/( float )n;
//Printing average wait time and turnaround time printf ( "The average wait time is : %lf\n" ,avg_wt);
printf ( "The average TurnAround time is : %lf\n" ,avg_tat);
return 0;
} |
Output:
Enter the number of processes : 4
Enter the time quanta : 2
Enter the process numbers : 1 2 3 4
Enter the arrival time of the processes : 0 1 2 3
Enter the burst time of the processes : 5 4 2 1
Program No. Arrival Time Burst Time Wait Time TurnAround Time
1 0 5 7 12
2 1 4 6 10
3 2 2 2 4
4 3 1 5 6
Average wait time : 5
Average Turn Around Time : 8
Program for Round Robin Scheduling with Different Arrival Times for all Processes
For detailed implementation of Preemptive Round Robin algorithm with different arrival times for all processes please refer: Program for Round Robin Scheduling with different arrival times.
Conclusion
In conclusion, Round Robin CPU scheduling is a fair and preemptive algorithm that allocates a fixed time quantum to each process, ensuring equal CPU access. It is simple to implement but can lead to higher context-switching overhead. While it promotes fairness and prevents starvation, it may result in longer waiting times and reduced throughput, depending on the time quantum. Effective program implementation allows for the calculation of key metrics like completion time, turnaround time, and waiting time, aiding in performance evaluation and optimization.