SJF Scheduling Program in C

Last Updated on November 28, 2023 by Ankit Kochar

The "shortest job first scheduling" method operates on the principle of prioritizing the completion of the shortest task first. This approach finds application in various real-world scenarios. For example, online delivery applications often employ this technique by choosing the nearest order for delivery as the initial task. Subsequently, upon completing the initial delivery, the system proceeds to identify the next nearby delivery location for efficiency.

What is the Shortest Job Scheduling?

One CPU scheduling strategy involves giving priority to the shortest jobs first, using an algorithm that depends on the burst time of processes. Simply put, processes with lower burst times are executed first. The term "Shortest Job Next" (SJN) is synonymous with "Shortest Job First" (SJF). Consider, for example, four processes – P1, P2, P3, and P4 – with burst times of 5, 7, 6, and 2, respectively. In this case, Process P4 is scheduled to run first due to its shorter burst period. Subsequently, Processes P1, P3, and P2 will be executed in that specific order.

Shortest Job First Scheduling Algorithm

Below are the steps to perform the SJF scheduling program in c.

• Firstly, we will begin the procedure.
• After that, we will Consider the number of elements to be inserted.
• Then, we will choose the process with the shortest burst time and will execute the first process.
• We will check that if both processes have the same burst time length then the FCFS scheduling algorithm is used.
• We will make the average waiting time for the next process.
• We will begin with the first process, make the above selection, and place the other processes in a queue.
• We will calculate burst time.
• We will display the values that are related.
• In the end, we will stop the process.
• Likewise, we will run all the steps until all the processes are executed.

Characteristics of Shortest Job Scheduling

• This algorithm is Greedy.
• It is helpful for batch processing.
• Shortest Job First has the benefit of having the quickest average waiting time out of all scheduling algorithms.
• By offering shorter assignments that must be finished first and often have a quicker turnaround time, enhances job output.

Shortest Job Scheduling Algorithm with an Example

Let’s look at an example of the implementation of the shortest job first scheduling method. Here, we’ve used an illustration to explain how the algorithm functions. To further comprehend it, we’ll also conduct a dry run.

In the above example, we have taken 4 processes P1, P2, P3, and P4 with an arrival time of 1,2,1, and 4 respectively. They also have burst times 3, 4, 2, and 4 respectively. Now, we need to create two queues the ready queue and the running queue which is also known as the Gantt chart.

Step 1: First, we will sort all the processes according to their arrival time.

In the above image, we can see that after performing a sort on arrival time order of the processes changes to P1, P3, P2, and P4.

Step 2: We will push all the processes into the ready queue with an arrival time of 0. In this example, we do not have processes that have 0 arrival times which is why we will push processes that have an arrival time of 1. In this example, we have P1 And P3 with an arrival time of 1. For time 0-1 running queue is in the ideal mode.

This is how queues will look after the completion of the second step.

In the above image, we can see that first process P3 is pushed into the ready queue and after that, process P1 is pushed. While running queue is in the ideal condition.

Step 3: After that, we will select a process that comes at an arrival time of 1 from the ready queue which has a minimum burst time. Here, P3 has the least burst time which is 2 and it is moved into the running queue. That’s why P3 is executed first.

Step 4: During the execution of P3, we will push P2 into the ready queue that has an arrival time of 2 because P3 runs till time 3. Now, in the ready queue, there are 2 processes available: P1, P2

Step 5: P3 finishes at time 3. Again we will select a process from the ready queue that has minimum burst time. In our ready queue, we have 2 processes P1 and P2. Among them, P1 has the minimum burst time which is 3. Then P1 enters into the running queue and it is executed till time 6.

Step 6: During the execution of P1, we will push P4 into the ready queue that has an arrival time of 4 because P1 runs till time 6. Now, in the ready queue, there are 2 processes available: P2, P4

After this, we do not have any new process to add to the ready queue so we will not modify the running queue.

Step 7: P1 completes on time 6. Again, we will choose a process from the ready queue with the shortest burst time. We have two processes in our ready queue: P2 and P4. In this case, both processes (P2, P4) have equal burst time which is 4. That is why we will select a process that has a minimum arrival time. So, P2 came on time 2 and P4 came on time 4 but P2 has a minimum arrival time compared to P4. That is why P2 is then added to the running queue and executed until time 10.

After this, we do not have any new process to add to the ready queue so we will not modify the running queue.
Step 8: P2 completes on time 10. Now, we have only one process (P4) in the ready queue which has burst time 4. P4 is moved to the running queue and executed until time 14.

After performing all the operations, our running queue also known as the Gantt chart will look like the below.

Let’s calculate the other terms like Completion time, Turn Around Time (TAT), Waiting Time (WT), and Response Time (RT). Below are the equations to calculate the above terms.

Turn Around Time = Completion Time – Arrival Time
Waiting Time = Turn Around Time – Burst Time

Average waiting time = Addition of waiting time of all processes divided by the number of processes

SJF Scheduling Program in C

We have already seen what is SJF scheduling and how SJF scheduling works. Now, We will see how to write the SJF scheduling program in c. We will use the above algorithm to write the SJF scheduling program in c.

// SJF scheduling program in c
#include<string.h>
int main()
{
    int bt[20],at[10],n,i,j,temp,st[10],ft[10],wt[10],ta[10];
    int totwt=0,totta=0;
    double awt,ata;
    char pn[10][10],t[10];
    //clrscr();
    printf("Enter the number of process:");
    scanf("%d",&n);
    for(i=0; i<n; i++)
    {
        printf("Enter process name, arrival time& burst time:");
        scanf("%s%d%d",pn[i],&at[i],&bt[i]);
    }
    for(i=0; i<n; i++)
        for(j=0; j<n; j++)
        {
            if(bt[i]<bt[j])
            {
                temp=at[i];
                at[i]=at[j];
                at[j]=temp;
                temp=bt[i];
                bt[i]=bt[j];
                bt[j]=temp;
                strcpy(t,pn[i]);
                strcpy(pn[i],pn[j]);
                strcpy(pn[j],t);
            }
        }
    for(i=0; i<n; i++)
    {
        if(i==0)
            st[i]=at[i];
        else
            st[i]=ft[i-1];
        wt[i]=st[i]-at[i];
        ft[i]=st[i]+bt[i];
        ta[i]=ft[i]-at[i];
        totwt+=wt[i];
        totta+=ta[i];
    }
    awt=(double)totwt/n;
    ata=(double)totta/n;
    printf("\nProcessname\tarrivaltime\tbursttime\twaitingtime\tturnaroundtime");
    for(i=0; i<n; i++)
    {
        printf("\n%s\t%5d\t\t%5d\t\t%5d\t\t%5d",pn[i],at[i],bt[i],wt[i],ta[i]);
    }
    printf("\nAverage waiting time: %f",awt);
    printf("\nAverage turnaroundtime: %f",ata);
    return 0;
}

Output

Enter the number of process:4
Enter process name, arrival time& burst time:
1
1 
3
Enter process name, arrival time& burst time:
2
2
4
Enter process name, arrival time& burst time:
3
1
2
Enter process name, arrival time& burst time:
4
4
4

Average waiting time: 3.000000
Average turnaround time: 6.250000

Read more:
10 Simple C Programs for Beginners

Advantages of the SJF Scheduling Algorithm

• Prioritization will be given to processes with the lowest burst time.
• This method generates a low average waiting time, making it incredibly effective.

Disadvantages of the SJF Scheduling Algorithm

• Short processes can lead to famine if they occur repeatedly. We can fix this issue by becoming older.
• This approach cannot be used to achieve short-term CPU scheduling.

Conclusion
In conclusion, Shortest Job First (SJF) scheduling proves to be a valuable CPU scheduling strategy in C programming. By prioritizing processes based on their burst times, this algorithm enhances efficiency and minimizes waiting times. The example scenario with processes P1, P2, P3, and P4 illustrated the practical application of SJF scheduling, showcasing how it optimally schedules processes for execution. When implementing SJF scheduling in C, developers can improve system performance and responsiveness, particularly in scenarios with varying process burst times.

FAQs Related to SJF Scheduling Program in C

Here are some of the FAQs related to SJF Scheduling Program in C:

Q1: What is SJF scheduling in C, and how does it work?
A1: SJF scheduling in C, or Shortest Job First scheduling, is a CPU scheduling strategy that prioritizes processes based on their burst times. The process with the shortest burst time is scheduled for execution first, reducing waiting times and improving overall system efficiency.

Q2: Can SJF scheduling lead to starvation of longer processes?
A2: Yes, SJF scheduling can potentially lead to starvation for longer processes, as they may continually be delayed by the arrival of shorter processes. To mitigate this, techniques such as aging or priority aging can be incorporated into the scheduling algorithm.

Q3: How is burst time determined in the context of SJF scheduling?
A3: Burst time in SJF scheduling refers to the time a process requires for execution. It is determined based on the actual time taken by the process to complete its execution.

Q4: Are there scenarios where SJF scheduling may not be the most suitable choice?
A4: Yes, SJF scheduling may face challenges in scenarios where accurate prediction of burst times is difficult. Additionally, in dynamic environments with frequent arrivals of short jobs, longer jobs might experience delays, potentially impacting overall system fairness.

Q5: What are some advantages of SJF scheduling in C programming?
A5: SJF scheduling in C offers advantages such as reduced waiting times, improved system throughput, and efficient utilization of CPU resources. It is particularly beneficial in scenarios where burst times are known or can be accurately predicted.

Q6: Can SJF scheduling be preemptive in nature?
A6: Yes, SJF scheduling can be preemptive, known as Shortest Remaining Time First (SRTF), where the scheduler can interrupt the currently running process if a new process with a shorter burst time arrives.

Q7: How is the turnaround time affected by SJF scheduling?
A7: SJF scheduling aims to minimize turnaround time by prioritizing the execution of processes with shorter burst times. This leads to quicker completion of processes, reducing overall turnaround time in the system.