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Program for FCFS CPU Scheduling | Set 2 (Processes with different arrival times)

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  • Difficulty Level : Easy
  • Last Updated : 21 Dec, 2022
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We have already discussed FCFS Scheduling of processes with same arrival time. In this post, scenarios, when processes have different arrival times, are discussed. Given n processes with their burst times and arrival times, the task is to find average waiting time and an average turn around time using FCFS scheduling algorithm. 
FIFO simply queues processes in the order they arrive in the ready queue. Here, the process that comes first will be executed first and next process will start only after the previous gets fully executed. 

  1. Completion Time: Time at which the 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.

ff2_ff23_

Process     Wait Time : Service Time - Arrival Time
   P0                        0 - 0   = 0
   P1                        5 - 1   = 4
   P2                        8 - 2   = 6
   P3                        16 - 3  = 13

Average Wait Time: (0 + 4 + 6 + 13) / 4 = 5.75

Service Time: Service time means the amount of time after which a process can start execution. It is summation of burst time of previous processes (Processes that came before)

Changes in code as compare to code of FCFS with same arrival time: To find waiting time: Time taken by all processes before the current process to be started (i.e. burst time of all previous processes) – arrival time of current process 
wait_time[i] = (bt[0] + bt[1] +…… bt[i-1] ) – arrival_time[i]

Implementation: 

1- Input the processes along with their burst time(bt)
   and arrival time(at)
2- Find waiting time for all other processes i.e. for
   a given process  i:
       wt[i] = (bt[0] + bt[1] +...... bt[i-1]) - at[i] 
3- Now find turn around time 
          = waiting_time + burst_time for all processes
4- Average waiting time = 
                    total_waiting_time / no_of_processes
5- Average turn around time = 
                 total_turn_around_time / no_of_processes

C++




//Process Synced, dynamic input, c++ easy to understand code
#include<iostream>
#include<stdlib.h>
using namespace std;
//class process with all the time values and functions
class Process{
    int id, bt, at, ct, tat, wt;
    public:
    void input(Process*,int );
    void calc(Process *,int);
    void show(Process*,int);
    void sort(Process *, int);
};
//main function
int main(){
    int n;
    cout<<"\nEnter the no of processes in your system:\n";
    cin>>n;
    Process *p = new Process[n];
    Process f;
    f.input(p,n);
    f.sort(p, n);
    f.calc(p,n);
    f.show(p,n);
    return 0;
}
//taking input arrival and burst times for all processes
void Process::input(Process *p,int n){
    for(int i = 0;i<n;i++){
        cout<<"\nEnter pival time for process "<<i+1<<":\n";
        cin>>p[i].at;
        cout<<"\nEnter burst time for process "<<i+1<<":\n";
        cin>>p[i].bt;
        p[i].id = i+1;
    }
}
//calculating waiting, turn-around and completion time
void Process::calc(Process*p, int n){
    int sum = 0;
    sum = sum + p[0].at;
    for(int i = 0;i<n;i++){
        sum = sum + p[i].bt;
        p[i].ct = sum;
        p[i].tat = p[i].ct - p[i].at;
        p[i].wt = p[i].tat - p[i].bt; 
        if(sum<p[i+1].at){
            int t = p[i+1].at-sum;
            sum = sum+t;
        }
    }
}
//Sorting processes with respect to arrival times (needed for synchronized input)
void Process::sort(Process*p, int n){
    for(int i=0;i<n-1;i++){
        for(int j=0;j<n-i-1;j++){
            if(p[j].at>p[j+1].at){
                int temp;
                //sorting burst times
                temp = p[j].bt;
                p[j].bt = p[j+1].bt;
                p[j+1].bt = temp;
                //sorting arrival times
                temp = p[j].at;
                p[j].at = p[j+1].at;
                p[j+1].at = temp;
                //sorting their respective IDs
                temp = p[j].id;
                p[j].id = p[j+1].id;
                p[j+1].id = temp;
            }
        }
    }
}
//display function
void Process::show(Process*p, int n){
    cout<<"Process\tArrival\tBurst\tWaiting\tTurn Around\tCompletion\n";
    for(int i =0;i<n;i++){
        cout<<"  P["<<p[i].id<<"]\t  "<<p[i].at<<"\t"<<p[i].bt<<"\t"<<p[i].wt<<"\t   "<<p[i].tat<<"\t\t"<<p[i].ct<<"\n";
    }
}

Java



// Java program for implementation of FCFS
// scheduling with different arrival time
public class GFG{
 
 
// Function to find the waiting time for all
// processes
static void findWaitingTime(int processes[], int n, int bt[], int wt[], int at[])
{
    int service_time[] = new int[n];
    service_time[0] = at[0];
    wt[0] = 0;
 
    // calculating waiting time
    for (int i = 1; i < n ; i++)
    {
        //representing wasted time in queue
        int wasted=0;
        // Add burst time of previous processes
        service_time[i] = service_time[i-1] + bt[i-1];
 
        // Find waiting time for current process =
        // sum - at[i]
        wt[i] = service_time[i] - at[i];
 
        // If waiting time for a process is in negative
        // that means it is already in the ready queue
        // before CPU becomes idle so its waiting time is 0
        // wasted time is basically time for process to wait after a process is over
        if (wt[i] < 0) {
            wasted = Math.abs(wt[i]);
            wt[i] = 0;
        }
        //Add wasted time
        service_time[i] = service_time[i] + wasted;
    }
}
 
// Function 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];
}
 
// Function to calculate average waiting and turn-around
// times.
static void findavgTime(int processes[], int n, int bt[], int at[])
{
    int wt[] = new int[n], tat[] = new int[n];
 
    // Function to find waiting time of all processes
    findWaitingTime(processes, n, bt, wt, at);
 
    // Function to find turn around time for all processes
    findTurnAroundTime(processes, n, bt, wt, tat);
 
    // Display processes along with all details
    System.out.print("Processes " + " Burst Time " + " Arrival Time "
        + " Waiting Time " + " Turn-Around Time "
        + " Completion Time \n");
    int total_wt = 0, total_tat = 0;
    for (int i = 0 ; i < n ; i++)
    {
        total_wt = total_wt + wt[i];
        total_tat = total_tat + tat[i];
        int compl_time = tat[i] + at[i];
        System.out.println(i+1 + "\t\t" + bt[i] + "\t\t"
            + at[i] + "\t\t" + wt[i] + "\t\t "
            + tat[i] + "\t\t " + compl_time);
    }
 
    System.out.print("Average waiting time = "
        + (float)total_wt / (float)n);
    System.out.print("\nAverage turn around time = "
        + (float)total_tat / (float)n);
}
 
// Driver code
 
    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[] = {5, 9, 6};
 
    // Arrival time of all processes
    int arrival_time[] = {0, 3, 6};
 
    findavgTime(processes, n, burst_time, arrival_time);
 
    }
}
 
/*This code is contributed by PrinciRaj1992*/
Python3



# Python3 program for implementation of FCFS
# scheduling with different arrival time
 
# Function to find the waiting time
# for all processes
def findWaitingTime(processes, n, bt, wt, at):
    service_time = [0] * n
    service_time[0] = 0
    wt[0] = 0
 
    # calculating waiting time
    for i in range(1, n):
         
        # Add burst time of previous processes
        service_time[i] = (service_time[i - 1] +
                                     bt[i - 1])
 
        # Find waiting time for current
        # process = sum - at[i]
        wt[i] = service_time[i] - at[i]
 
        # If waiting time for a process is in
        # negative that means it is already
        # in the ready queue before CPU becomes
        # idle so its waiting time is 0
        if (wt[i] < 0):
            wt[i] = 0
     
# Function to calculate turn around time
def findTurnAroundTime(processes, n, bt, wt, tat):
     
    # Calculating turnaround time by
    # adding bt[i] + wt[i]
    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, at):
    wt = [0] * n
    tat = [0] * n
 
    # Function to find waiting time
    # of all processes
    findWaitingTime(processes, n, bt, wt, at)
 
    # 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   Arrival Time     Waiting",
          "Time   Turn-Around Time  Completion Time \n")
    total_wt = 0
    total_tat = 0
    for i in range(n):
 
        total_wt = total_wt + wt[i]
        total_tat = total_tat + tat[i]
        compl_time = tat[i] + at[i]
        print(" ", i + 1, "\t\t", bt[i], "\t\t", at[i],
              "\t\t", wt[i], "\t\t ", tat[i], "\t\t ", compl_time)
 
    print("Average waiting time = %.5f "%(total_wt /n))
    print("\nAverage turn around time = ", total_tat / n)
 
# Driver code
if __name__ =="__main__":
     
    # Process id's
    processes = [1, 2, 3]
    n = 3
 
    # Burst time of all processes
    burst_time = [5, 9, 6]
 
    # Arrival time of all processes
    arrival_time = [0, 3, 6]
 
    findavgTime(processes, n, burst_time,
                            arrival_time)
 
# This code is contributed
# Shubham Singh(SHUBHAMSINGH10)
C#



// C# program for implementation of FCFS
// scheduling with different arrival time
using System;
     
public class GFG{
  
  
// Function to find the waiting time for all
// processes
static void findWaitingTime(int []processes, int n, int []bt, int []wt, int []at)
{
    int []service_time = new int[n];
    service_time[0] = 0;
    wt[0] = 0;
  
    // calculating waiting time
    for (int i = 1; i < n ; i++)
    {
        // Add burst time of previous processes
        service_time[i] = service_time[i-1] + bt[i-1];
  
        // Find waiting time for current process =
        // sum - at[i]
        wt[i] = service_time[i] - at[i];
  
        // If waiting time for a process is in negative
        // that means it is already in the ready queue
        // before CPU becomes idle so its waiting time is 0
        if (wt[i] < 0)
            wt[i] = 0;
    }
}
  
// Function 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];
}
  
// Function to calculate average waiting and turn-around
// times.
static void findavgTime(int []processes, int n, int []bt, int []at)
{
    int []wt = new int[n]; int []tat = new int[n];
  
    // Function to find waiting time of all processes
    findWaitingTime(processes, n, bt, wt, at);
  
    // Function to find turn around time for all processes
    findTurnAroundTime(processes, n, bt, wt, tat);
  
    // Display processes along with all details
    Console.Write("Processes " + " Burst Time " + " Arrival Time "
        + " Waiting Time " + " Turn-Around Time "
        + " Completion Time \n");
    int total_wt = 0, total_tat = 0;
    for (int i = 0 ; i < n ; i++)
    {
        total_wt = total_wt + wt[i];
        total_tat = total_tat + tat[i];
        int compl_time = tat[i] + at[i];
        Console.WriteLine(i+1 + "\t\t" + bt[i] + "\t\t"
            + at[i] + "\t\t" + wt[i] + "\t\t "
            + tat[i] + "\t\t " + compl_time);
    }
  
    Console.Write("Average waiting time = "
        + (float)total_wt / (float)n);
    Console.Write("\nAverage turn around time = "
        + (float)total_tat / (float)n);
}
  
// Driver code
  
    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 = {5, 9, 6};
  
    // Arrival time of all processes
    int []arrival_time = {0, 3, 6};
  
    findavgTime(processes, n, burst_time, arrival_time);
  
    }
}
// This code is contributed by Princi Singh
Javascript



<script>
  
// JavaScript program for implementation of FCFS
// scheduling with different arrival time
  
// Function to find the waiting time for all
// processes
function findWaitingTime(processes , n , bt , wt , at)
{
    var service_time = Array.from({length: n}, (_, i) => 0);
    service_time[0] = at[0];
    wt[0] = 0;
  
    // calculating waiting time
    for (var i = 1; i < n ; i++)
    {
        //representing wasted time in queue
        var wasted=0;
        // Add burst time of previous processes
        service_time[i] = service_time[i-1] + bt[i-1];
  
        // Find waiting time for current process =
        // sum - at[i]
        wt[i] = service_time[i] - at[i];
  
        // If waiting time for a process is in negative
        // that means it is already in the ready queue
        // before CPU becomes idle so its waiting time is 0
        // wasted time is basically time for process to
        // wait after a process is over
        if (wt[i] < 0) {
            wasted = Math.abs(wt[i]);
            wt[i] = 0;
        }
        // Add wasted time
        service_time[i] = service_time[i] + wasted;
    }
}
  
// Function to calculate turn around time
function findTurnAroundTime(processes , n , bt, wt , tat)
{
    // Calculating turnaround time by adding bt[i] + wt[i]
    for (var i = 0; i < n ; i++)
        tat[i] = bt[i] + wt[i];
}
  
// Function to calculate average waiting and turn-around
// times.
function findavgTime(processes , n , bt , at)
{
    var wt = Array.from({length: n}, (_, i) => 0.0);
    var tat = Array.from({length: n}, (_, i) => 0.0);
  
    // Function to find waiting time of all processes
    findWaitingTime(processes, n, bt, wt, at);
  
    // 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 " + " Arrival Time "
        + " Waiting Time " + " Turn-Around Time "
        + " Completion Time <br>");
    var total_wt = 0, total_tat = 0;
    for (var i = 0 ; i < n ; i++)
    {
        total_wt = total_wt + wt[i];
        total_tat = total_tat + tat[i];
        var compl_time = tat[i] + at[i];
        document.write(i+1 + "  " + bt[i]
        + "  "
            + at[i] + "  " + wt[i] + "  "
            + tat[i] + "  " + compl_time+"<br>");
    }
  
    document.write("<br>Average waiting time = "
        + total_wt/n +"<br>");
    document.write("<br>Average turn around time = "
        + total_tat/n+"<br>");
}
  
// Driver code
  
       
    // Process id's
   var processes = [1, 2, 3];
   var n = processes.length;
  
// Burst time of all processes
var burst_time = [5, 9, 6];
  
// Arrival time of all processes
var arrival_time = [0, 3, 6];
  
findavgTime(processes, n, burst_time, arrival_time);
  
  
  
// This code is contributed by 29AjayKumar
  
</script>
Output: 
Processes  Burst Time  Arrival Time  Waiting Time  Turn-Around Time  Completion Time 
 1        5        0        0         5         5
 2        9        3        2         11         14
 3        6        6        8         14         20
Average waiting time = 3.33333
Average turn around time = 10.0
This article is contributed by Sahil Chhabra. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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