Priority Scheduling in C

Priority scheduling is an important concept in computer science that deals with the efficient allocation of resources. In a priority scheduling program, processes are assigned a priority level based on their importance, and the system allocates resources to them accordingly. The goal is to ensure that high-priority processes receive the resources they need to complete their tasks in a timely manner, while low-priority processes do not interfere with the execution of high-priority processes.

In a priority scheduling program in C, the efficiency of the algorithm is calculated based on the average waiting and turnaround time. There are possibilities for a process having low priority to fall into a state of starvation for resources. To prevent this from happening, a solution to the problem of indefinite blockage of the low-priority process is aging. In this way, the priority scheduling program in C ensures that all processes are treated fairly and that resources are allocated in the most efficient manner possible.

Overview of Priority Scheduling

In priority scheduling, the CPU executes the process with the highest priority first. The priority of a process is determined by factors such as its execution time, memory requirements, and resource requirements. This algorithm is widely used in operating systems and real-time systems to manage processes efficiently.

Definition of Priority Scheduling

Priority scheduling is a scheduling algorithm that determines the order in which processes are executed based on their priority. Each process is assigned a priority value, which is used to determine the order in which it is executed. The process with the highest priority value is executed first.

Types of Priority Scheduling

There are two types of priority scheduling algorithms – preemptive and non-preemptive. In preemptive priority scheduling, the CPU can interrupt a running process and switch to a higher priority process. In non-preemptive priority scheduling, the CPU does not interrupt a running process and waits for it to finish before executing the next process.

In both types of priority scheduling, if two processes have the same priority value, then the scheduling is done on a first-come, first-serve (FCFS) basis.

In non-preemptive priority scheduling, there is a risk of starvation, where a process with a low priority value may never get executed. To prevent starvation, the aging technique can be used, where the priority value of a process increases as it waits in the ready queue.

Implementation of Priority Scheduling in C

The implementation of priority scheduling in C involves creating a struct process that stores the process ID, burst time, priority number, and other necessary information. The processes are stored in an array, and the array is sorted based on the priority value of each process.

The code for priority scheduling in C involves inputting the processes with their burst time and priority, sorting the processes based on priority, and applying the FCFS algorithm. The output includes the waiting time, turnaround time, and average turnaround time of each process.

The time complexity of the priority scheduling algorithm is O(nlogn), where n is the number of processes. The space complexity is O(n).

Conclusion

Priority scheduling is an efficient algorithm for managing processes in operating systems and real-time systems. It ensures that processes with higher priority are executed first, leading to better resource utilization and efficiency. The implementation of priority scheduling in C involves creating a struct process, sorting the processes based on priority, and applying the FCFS algorithm.

Preemptive Priority Scheduling

Definition

Preemptive Priority Scheduling is a CPU scheduling algorithm that works based on the priority of a process. In this algorithm, the scheduler schedules the tasks to work as per the priority, which means that a higher priority process should be executed first. The algorithm works in a preemptive manner, which means that the currently executing process can be interrupted by a higher priority process at any time.

Algorithm

The algorithm works by assigning a priority number to each process. The process with the highest priority number is executed first. If two processes have the same priority number, then the scheduling is done on a First Come First Serve (FCFS) basis. The algorithm works in a preemptive manner, which means that the currently executing process can be interrupted by a higher priority process at any time.

The algorithm works as follows:

1. Assign a priority number to each process.
2. The process with the highest priority number is executed first.
3. If two processes have the same priority number, then the scheduling is done on a First Come First Serve (FCFS) basis.
4. The currently executing process can be interrupted by a higher priority process at any time.

Implementation in C

To implement the Preemptive Priority Scheduling algorithm in C, we need to create a struct process that will hold the information about each process. The struct process will have the following fields:

• id: the process ID
• burst_time: the time required by the process to complete its execution
• priority: the priority of the process
• arrival_time: the time at which the process arrives in the ready queue
• waiting_time: the time the process has spent waiting in the ready queue
• turnaround_time: the time the process takes to complete its execution

We will also need to create a job queue and a ready queue. The job queue will hold all the processes that are waiting to be executed, and the ready queue will hold all the processes that are ready to be executed.

We can implement the algorithm using the following steps:

1. Read the input from the user, which includes the number of processes, burst time, priority, and arrival time for each process.
2. Create a struct process for each process and add it to the job queue.
3. Sort the job queue based on the arrival time of the processes.
4. Initialize the current time to 0.
5. While the job queue is not empty or the ready queue is not empty:
   • Move all the processes that have arrived in the job queue to the ready queue.
   • Sort the ready queue based on the priority of the processes.
   • Execute the process at the front of the ready queue for one unit of time.
   • If the process has completed its execution, remove it from the ready queue and calculate its waiting time and turnaround time.
   • If there is a process with a higher priority than the currently executing process, preempt it and add the currently executing process to the ready queue.
   • Increment the current time by one unit.
6. Calculate the average waiting time and average turnaround time.

Here is a sample code for the Preemptive Priority Scheduling algorithm in C:

#include<stdio.h>
#include<stdlib.h>

struct process {
    int id;
    int burst_time;
    int priority;
    int arrival_time;
    int waiting_time;
    int turnaround_time;
};

int main() {
    int n, i, j;
    float total_wt = 0, total_tat = 0, avg_wt, avg_tat;
    struct process p[100], temp;
    printf("Enter the number of processes: ");
    scanf("%d", &n);
    for(i=0;i<n;i++) {
        printf("Enter the burst time, priority, and arrival time of process %d: ", i+1);
        scanf("%d %d %d", &p[i].burst_time, &p[i].priority, &p[i].arrival_time);
        p[i].id = i+1;
    }
    for(i=0;i<n-1;i++) {
        for(j=0;j<n-i-1;j++) {
            if(p[j].arrival_time > p[j+1].arrival_time) {
                temp = p[j];
                p[j] = p[j+1];
                p[j+1] = temp;
            }
        }
    }
    int current_time = 0;
    int count = 0;
    int pt[100];
    while(count < n) {
        for(i=0;i<n;i++) {
            if(p[i].arrival_time == current_time) {
                pt[count] = i;
                count++;
            }
        }
        int min_priority = 9999;
        int min_index = -1;
        for(i=0;i<count;i++) {
            if(p[pt[i]].

Non-Preemptive Priority Scheduling

In the world of operating systems, process scheduling is an essential task that needs to be performed efficiently. One of the most widely used scheduling algorithms is the Priority Scheduling algorithm. In this section, we will discuss the Non-Preemptive Priority Scheduling algorithm in detail.

Definition

The Non-Preemptive Priority Scheduling algorithm is a process scheduling algorithm in which each process is assigned a priority value, and the process with the highest priority is executed first. In this algorithm, once a process starts executing, it is not interrupted until it completes its execution or enters into the waiting state.

Algorithm

The Non-Preemptive Priority Scheduling algorithm works on the following principles:

1. Assign a priority value to each process.
2. The process with the highest priority is executed first.
3. If two processes have the same priority, then the process that arrived first is executed first.

Implementation in C

Let’s take a look at how we can implement the Non-Preemptive Priority Scheduling algorithm in C programming language.

We start by defining a structure to store the details of each process, such as the process ID, arrival time, burst time, and priority number.

struct process {
    int pid;
    int arrivaltime;
    int bursttime;
    int prioritynumber;
};

Next, we create an array of structures to store the details of all the processes.

struct process pt[10];

We then take input from the user for the number of processes and their details such as arrival time, burst time, and priority number.

printf("Enter the number of processes: ");
scanf("%d", &n);

for (i = 0; i < n; i++) {
    printf("Enter the arrival time, burst time, and priority number of process %d: ", i+1);
    scanf("%d %d %d", &pt[i].arrivaltime, &pt[i].bursttime, &pt[i].prioritynumber);
    pt[i].pid = i+1;
}

We then sort the processes based on their priority number using the Selection Sort algorithm.

for (i = 0; i < n; i++) {
    pos = i;
    for (j = i+1; j < n; j++) {
        if (pt[j].prioritynumber < pt[pos].prioritynumber)
            pos = j;
    }
    temp = pt[i];
    pt[i] = pt[pos];
    pt[pos] = temp;
}

Finally, we calculate the turnaround time and waiting time for each process and output the results.

for (i = 0; i < n; i++) {
    tat = tat + pt[i].bursttime;
    pt[i].tat = tat - pt[i].arrivaltime;
    wt = wt + pt[i].tat - pt[i].bursttime;
    pt[i].waitingtime = wt;
}

printf("nProcessttBurst TimetArrival TimetPriority NumbertTurnaround TimetWaiting Timen");

for (i = 0; i < n; i++) {
    printf("%dtt%dtt%dtt%dtt%dtt%dn", pt[i].pid, pt[i].bursttime, pt[i].arrivaltime, pt[i].prioritynumber, pt[i].tat, pt[i].waitingtime);
}

Conclusion

The Non-Preemptive Priority Scheduling algorithm is a widely used scheduling algorithm in operating systems. It assigns a priority value to each process and executes the process with the highest priority first. In this section, we discussed the definition, algorithm, and implementation of the Non-Preemptive Priority Scheduling algorithm in C programming language.

Advantages and Disadvantages of Priority Scheduling

Advantages

Priority scheduling is a widely used scheduling algorithm in operating systems. It has several advantages over other scheduling algorithms. Here are some of the benefits of using priority scheduling:

• Efficient resource utilization: Priority scheduling ensures that high priority processes are executed first, which leads to efficient utilization of resources. This means that important tasks are completed quickly, and the CPU is not idle for long periods.
• Improved system performance: Priority scheduling can improve system performance by ensuring that important processes are executed first. This can lead to faster response times and better overall system performance.
• Flexible priority assignment: Priority scheduling allows for flexible priority assignment based on various factors such as time of execution, memory requirements, and other factors. This means that important tasks can be assigned higher priorities to ensure faster execution.

Disadvantages

While priority scheduling has several advantages, it also has some disadvantages. Here are some of the drawbacks of using priority scheduling:

• Starvation of low priority processes: If high priority processes take up a lot of CPU time, then low priority processes may starve and be postponed indefinitely. This can lead to reduced system performance and slow response times.
• Inefficient utilization of resources: If the priority of a process is set too high, it may monopolize system resources, leading to inefficient utilization of resources. This can lead to reduced system performance and slow response times.
• Difficulty in defining priorities: Defining priorities can be difficult, especially if there are many processes running simultaneously. This can lead to inefficient resource utilization and reduced system performance.

In conclusion, priority scheduling has several advantages and disadvantages. It is important to carefully consider these factors when choosing a scheduling algorithm for an operating system.

Real-World Applications of Priority Scheduling

Priority scheduling is a widely used algorithm in operating systems today. It is used to schedule processes based on their priority levels. In this section, we will discuss some real-world applications of priority scheduling.

Batch Systems

Batch systems are used in large-scale data processing applications. They are designed to process large amounts of data in a batch mode. In batch systems, priority scheduling is used to determine the order in which jobs are executed. Jobs with higher priority levels are executed first. This helps to ensure that critical jobs are completed on time.

Real-Time Systems

Real-time systems are used in applications where time is critical. These systems are designed to respond to events within a specific time frame. In real-time systems, priority scheduling is used to ensure that the most critical tasks are executed first. This helps to ensure that the system responds to events within the required time frame.

Priority scheduling is used in a wide range of applications, including:

• Multimedia applications
• Real-time database systems
• Network applications
• Web servers
• Operating systems

In conclusion, priority scheduling is a versatile algorithm that is used in many real-world applications. Its ability to prioritize tasks based on their importance makes it an essential component in modern operating systems.