Module 8: Process Synchronization

Introduction to Synchronization

• Definition: Coordination needed when two processes access a shared resource.
• Purpose: Maintain consistency of shared resources to prevent operational inconsistency.
• Importance: Essential for maintaining OS integrity and has security implications due to potential race conditions.

Objectives

• Coordinate processes sharing resources.
• Protect memory regions with locks.
• Maintain consistency of shared data.

Reasons for Synchronization

• Resource Sharing: Needed in environments where multiple processes cooperate.
• Examples:
  • Buffer sharing between a producer and consumer.
  • Scheduling for better CPU and I/O time utilization.
• Benefits: Modularity and convenience in software development.

Buffer Sharing Problem

• Setup: Producer adds to buffer, consumer removes from buffer.
• Rules:
  • Producer must not add to a full buffer.
  • Consumer must not remove from an empty buffer.
• Solution: Implement a synchronization mechanism to enforce these rules.

Critical Section and Mutual Exclusion

• Critical Section: Code block where shared resources are accessed.
• Problem: Inconsistent state when two processes access a shared data.
• Solution: Mutual exclusion - ensuring only one process accesses the critical section at a time.

Semaphore and Monitors

• Semaphore: A synchronization tool with an integer value.
  • Operations: wait (decrement) and signal (increment).
• Binary Semaphore: Represents lock/unlock states, used as mutex locks.
• Monitors: Higher-level synchronization construct.

Reader-Writer Problem

• Scenario: Multiple readers, single writer.
• Conditions:
  • Multiple readers can read simultaneously.
  • Only one writer can write at a time.
  • No reading during writing.
• Solution: Use semaphores for synchronization.
  • Mutex for read count management.
  • WRT semaphore for controlling access to writing.

Implementing Synchronization

• Atomic Instructions: Essential for implementing semaphores.
• Examples: Test and set, swap instructions in microprocessors.
• Deadlock Prevention: Ensure no circular wait conditions.

Key Concepts

• Mutual Exclusion: Only one process accesses critical section among n processes.
• Progress: Process should enter critical section if no others are present.
• Bounded Waiting: Process should access critical section within a bounded time.

Implications

• Deadlock: Conditions leading to perpetual blocking.
• Security: Synchronization critical for preventing race conditions and denial of service.

Summary

• Synchronization is key for operating system consistency and security.
• Understanding critical sections, semaphores, and mutual exclusion is crucial for OS administration and security.
• Further reading: textbooks like Galvin and MOOC courses on operating systems.

Note: This lecture provides a foundational understanding, further study recommended for comprehensive knowledge.