Priority Scheduling in OS: A Comprehensive Guide

Introduction

In operating systems, process scheduling is essential for efficient task execution. Priority Scheduling is a widely used algorithm where each process is assigned a priority, determining its execution order. This approach ensures critical tasks complete first, making it ideal for real-time and embedded systems.

What is Priority Scheduling?

Priority scheduling is a CPU scheduling algorithm where processes are executed based on their assigned priority. The scheduler selects the highest-priority process for execution. If multiple processes have the same priority, they follow First-Come, First-Served (FCFS) order.

Priority scheduling can be classified as:

• Preemptive: A high-priority process interrupts a running lower-priority process.
• Non-Preemptive: Once a process starts, it runs until completion before another process is executed.

How Priority Scheduling Works

1. Each process is assigned a priority value.
2. The scheduler selects the highest-priority process.
3. If a new process with a higher priority arrives (in preemptive scheduling), it replaces the current process.
4. If multiple processes have the same priority, FCFS order is followed.
5. Execution continues until all processes are completed.

Types of Priority Scheduling

1. Preemptive Priority Scheduling

• Higher-priority processes can interrupt lower-priority ones.
• Ensures critical tasks complete first.
• May lead to starvation (low-priority processes never execute).

2. Non-Preemptive Priority Scheduling

• Processes run to completion once started.
• Simple to implement but may delay high-priority tasks.

Advantages of Priority Scheduling

✔️ Ensures critical tasks complete first. ✔️ Efficient for real-time applications. ✔️ Reduces response time for high-priority processes.

Disadvantages of Priority Scheduling

❌ Starvation: Low-priority processes may never execute. ❌ Complexity: Requires priority assignment and management. ❌ CPU Overhead: Preemptive scheduling increases context switching.

Preventing Starvation with Aging

Aging is a technique where the priority of a waiting process gradually increases over time, ensuring eventual execution.

Comparison with Other Scheduling Algorithms

Practical Applications of Priority Scheduling

✅ Operating Systems: Windows, Linux, and real-time OS use priority scheduling for task management. ✅ Cloud Computing: Allocates resources dynamically based on priority. ✅ Healthcare Systems: Ensures critical patient monitoring tasks execute first. ✅ Financial Systems: Processes high-value transactions with higher priority.

Implementing Priority Scheduling in Programming

Here’s a simple Python implementation of Non-Preemptive Priority Scheduling:

class Process:
    def __init__(self, id, priority, burst_time):
        self.id = id
        self.priority = priority
        self.burst_time = burst_time

def priority_scheduling(processes):
    processes.sort(key=lambda x: x.priority)  # Sorting by priority
    print("Execution Order: ", [p.id for p in processes])

# Example
processes = [Process(1, 2, 10), Process(2, 1, 5), Process(3, 3, 8)]
priority_scheduling(processes)

Conclusion

Priority Scheduling is a crucial algorithm for managing process execution in operating systems. While it optimizes resource allocation, handling starvation with aging techniques is essential.

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