Pre-emptive Shortest Job First Scheduling Example (Operating Systems)

Pre-emptive Shortest Job First Scheduling Example (Operating Systems)

05:56

Description: Following C++ code runs a simulation to show how process scheduling in operating system is done using the job scheduling algorithm Shortest Job First and also taking into account the concept of pre-emption. Pre-emptive SJF is one of the many scheduling algorithms in operating system.

#include<iostream>

#include<windows.h>

using namespace std;

struct Node{

    int p_id;

    int arr_time;

    int exe_time;

    int sum;

    int rem_time;

};

int main(){

    int i, j, min = 100000, no_of_processes;

   

    cout<<"\n\t*** --> Pre-emptive Shortest Job First Scheduling <--   ***\n\n";

   

    cout<<"Enter no. of Processes:";

    cin>>no_of_processes;

   

    Node *Queue = new Node[no_of_processes];

   

    for (i = 0; i<no_of_processes; i++){

       

        cout << "\n\nGive Process#" << i + 1 << " id :";

        cin>>Queue[i].p_id;

       

        cout<<"\nGive Arrival Time (0~23):";

        cin>>Queue[i].arr_time;

       

        if (Queue[i].arr_time<min)

            min = i;

       

        cout<<"\nGive Execution Time (in secs.):";

        cin>>Queue[i].exe_time;

       

        Queue[i].sum = 0;

        Queue[i].rem_time = Queue[i].exe_time;

    }

    int time = 0, count = 0;

    i = min;

    while (count<no_of_processes){

       

        cout << "Process#" << Queue[i].p_id<<" executing\t(Total Time Elapsed : "<<time<<"secs.)\n";

        cout << "--> " << ++Queue[i].sum << endl;

       

        Sleep(1000);

       

        Queue[i].rem_time--;

        if (Queue[i].rem_time == 0)

            count++;

        time++;

       

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

            if (Queue[j].rem_time != 0 && time >= Queue[j].arr_time){

                min = j;

                break;

            }

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

            if (Queue[j].rem_time != 0 && Queue[j].rem_time <= Queue[min].rem_time&&time >= Queue[j].arr_time)

                min = j;

       

        i = min;

    }

    system("pause");

    return 0;

}