# Program for Round Robin scheduling | Set 1

• Difficulty Level : Medium
• Last Updated : 21 Sep, 2021

Round Robin is a CPU scheduling algorithm where each process is assigned a fixed time slot in a cyclic way.

• It is simple, easy to implement, and starvation-free as all processes get fair share of CPU.
• One of the most commonly used technique in CPU scheduling as a core.
• It is preemptive as processes are assigned CPU only for a fixed slice of time at most.

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Illustration:

How to compute below times in Round Robin using a program?

1. Completion Time: Time at which process completes its execution.
2. Turn Around Time: Time Difference between completion time and arrival time. Turn Around Time = Completion Time – Arrival Time
3. Waiting Time(W.T): Time Difference between turn around time and burst time.
Waiting Time = Turn Around Time – Burst Time

In this post, we have assumed arrival times as 0, so turn around and completion times are same.
The tricky part is to compute waiting times. Once waiting times are computed, turn around times can be quickly computed.
Steps to find waiting times of all processes:

1- 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)
2- Create another array wt[] to store waiting times
of processes. Initialize this array as 0.
3- Initialize time : t = 0
4- Keep traversing the all processes while all processes
are not done. Do following for i'th process if it is
not done yet.
a- If rem_bt[i] > quantum
(i)  t = t + quantum
(ii) rem_bt[i] -= quantum;
c- Else // Last cycle for this process
(i)  t = t + rem_bt[i];
(ii) wt[i] = t - bt[i]
(ii) 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++

 // C++ program for implementation of RR scheduling#includeusing namespace std; // Function to find the waiting time for all// processesvoid 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 timevoid 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 timevoid 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 << "Processes "<< " Burst time "        << " Waiting time " << " Turn around time\n";     // Calculate total waiting time and total turn    // around time    for (int i=0; i

## Java

 // 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("Processes " + " Burst time " +                      " Waiting time " + " Turn around time");              // Calculate total waiting time and total turn        // around time        for (int i=0; i

## Python3

 # Python3 program for implementation of# RR scheduling # Function to find the waiting time# for all processesdef 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 timedef 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 codeif __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#

 // C# program for implementation of RR// schedulingusing 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.

## Javascript



Output:

Processes  Burst time  Waiting time  Turn around time
1        10     13         23
2        5     10         15
3        8     13         21
Average waiting time = 12
Average turn around time = 19.6667

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