Process Synchronization and Scheduling in Operating Systems

Day 5: Process Synchronization and Scheduling in Operating Systems

Date: January 17, 2025

As we wrap up this series on operating systems, we delve into two crucial aspects that ensure smooth multitasking and efficiency: process synchronization and scheduling. These concepts lie at the heart of how modern operating systems manage resources and execute tasks seamlessly.

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Goals for the Day

1. Understand process synchronization and its importance in multitasking.
2. Learn about CPU scheduling algorithms and their role in optimizing performance.

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Topics to Cover

What is Process Synchronization?

Process synchronization ensures that multiple processes can execute concurrently without interference or resource conflicts. It's essential for maintaining data consistency and preventing race conditions.

Key Concepts in Process Synchronization

1. Critical Section Problem:

   • A critical section is a part of a program where shared resources are accessed.
   • The problem arises when multiple processes attempt to access shared resources simultaneously.

2. Mutual Exclusion:

   • Ensures that only one process enters the critical section at a time.

3. Semaphores and Locks:

   • Semaphore: A signaling mechanism used to manage access to shared resources.
     • Types: Binary (mutex) and Counting semaphores.
   • Locks: Prevent multiple processes from accessing a resource simultaneously.

4. Deadlock and Starvation:

   • Deadlock: Occurs when processes are stuck, waiting indefinitely for resources held by each other.
   • Starvation: Happens when a process waits indefinitely due to resource allocation priorities.

Examples of Synchronization Mechanisms:

• Peterson’s Algorithm.
• Monitors.
• Reader-Writer Locks.

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What is Process Scheduling?

Process scheduling determines the order in which processes are executed by the CPU. It maximizes CPU utilization, throughput, and responsiveness while minimizing turnaround time and waiting time.

Types of Scheduling:

1. Long-Term Scheduling:

   • Decides which processes to admit into the system.

2. Medium-Term Scheduling:

   • Manages processes in memory by swapping them in or out.

3. Short-Term Scheduling:

   • Determines which process gets CPU time next.

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CPU Scheduling Algorithms

1. First-Come, First-Served (FCFS):

• Processes are executed in the order they arrive.
• Advantage: Simple to implement.
• Disadvantage: May cause long waiting times (convoy effect).

2. Shortest Job Next (SJN):

• Executes the process with the shortest execution time first.
• Advantage: Reduces waiting time.
• Disadvantage: Can lead to starvation.

3. Round Robin (RR):

• Each process gets a fixed time slice (quantum) in a cyclic order.
• Advantage: Ensures fairness.
• Disadvantage: Context switching overhead.

4. Priority Scheduling:

• Executes processes based on priority.
• Advantage: Critical tasks are handled first.
• Disadvantage: May cause starvation for lower-priority processes.

5. Multi-Level Queue Scheduling:

• Divides processes into multiple queues based on their priority or type.
• Each queue can use different scheduling algorithms.

6. Multi-Level Feedback Queue Scheduling:

• Processes move between queues based on their behavior and execution time.
• Advantage: Balances responsiveness and efficiency.

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Activities

1. Read/Watch:

• Refer to Operating System Concepts by Silberschatz for an in-depth explanation.
• Watch videos on synchronization techniques and CPU scheduling algorithms.

2. Hands-On Practice:

• Use a simulator to understand scheduling algorithms (e.g., CPU Scheduling Simulator tools).
• Implement a small program in Java or Python to simulate Round Robin scheduling.

Practical Task:

Write a program to simulate the Producer-Consumer problem using semaphores. This will help you understand synchronization practically.

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Interview Preparation

Common Questions:

1. What is a critical section, and why is it important?

   • A critical section is a part of a program where shared resources are accessed. Proper management ensures data consistency and avoids conflicts.

2. Explain the difference between deadlock and starvation.

   • Deadlock: Processes wait indefinitely due to circular resource dependency.
   • Starvation: A process waits indefinitely because higher-priority processes are always executed first.

3. What are the advantages of Round Robin scheduling?

   • Fairness in CPU allocation and better response times for interactive systems.

4. How does a semaphore work in process synchronization?

   • A semaphore controls access to shared resources by maintaining a counter.

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Outcome

By the end of Day 5, you should:

1. Understand the mechanisms and importance of process synchronization.
2. Be able to explain and implement basic CPU scheduling algorithms.
3. Gain insights into how operating systems manage multitasking and resource allocation.

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This concludes our five-day journey into the fascinating world of operating systems. With a solid foundation in OS concepts, you’re now better equipped to tackle both academic and practical challenges. Let me know if you’d like additional resources or clarifications on any of the topics!