Operating System
Process Synchronization
Process Synchronization is a mechanism used by Operating Systems to coordinate multiple processes or threads that access shared resources. When several processes execute simultaneously, improper access to shared data may lead to inconsistent results.
Synchronization ensures that processes execute in a safe, controlled, and coordinated manner without causing conflicts, data corruption, or unexpected behavior.
Critical Section Problem
A critical section is a part of a program where shared resources such as variables, files, or memory are accessed. Only one process should execute inside the critical section at a time.
- Shared resources must be protected from simultaneous access.
- Multiple processes entering together may produce incorrect output.
- Synchronization techniques solve this problem.
Requirements for a Good Synchronization Solution
- Mutual Exclusion: Only one process enters critical section at a time.
- Progress: Waiting processes should eventually get access.
- Bounded Waiting: No process should wait forever.
Race Condition
A race condition occurs when multiple processes access and modify shared data simultaneously, causing unpredictable results.
Race Condition Example
Process P1
- Read X = 5
- Increment X
- Write X = 6
Process P2
- Read X = 5
- Increment X
- Write X = 6
Expected Value = 7
Actual Value = 6
Mutex Lock
Mutex stands for Mutual Exclusion. A mutex lock allows only one process to access the critical section at a time.
- Process must acquire lock before entering critical section.
- Lock is released after execution.
- Other processes wait until lock becomes free.
Semaphore
A semaphore is a synchronization tool used to manage access to shared resources.
- Integer variable used for synchronization.
- Two operations: wait() and signal().
- Helps avoid race conditions.
| Operation | Purpose |
|---|---|
| wait() | Decreases semaphore value |
| signal() | Increases semaphore value |
Types of Semaphores
Binary Semaphore
- Value can be 0 or 1
- Works similar to mutex
- Allows single process access
Counting Semaphore
- Value can be greater than 1
- Controls multiple resources
- Used in resource allocation
Producer Consumer Problem
This classic synchronization problem occurs when producers generate data while consumers use it.
- Producer adds items to buffer
- Consumer removes items from buffer
- Synchronization prevents overflow and underflow
Dining Philosophers Problem
This synchronization problem demonstrates deadlock and resource sharing among processes.
- Five philosophers sit around a table.
- Each philosopher needs two forks to eat.
- Improper synchronization can cause deadlock.
Monitor
A monitor is a high-level synchronization construct that allows only one process to execute inside it at a time.
- Provides automatic mutual exclusion
- Simplifies synchronization programming
- Used in modern programming languages
Advantages of Synchronization
- Prevents data inconsistency
- Avoids race conditions
- Ensures proper resource sharing
- Improves system reliability
- Supports concurrent execution safely
Summary
Process Synchronization is essential in multi-tasking operating systems where multiple processes share resources. Synchronization mechanisms such as mutexes, semaphores, and monitors help maintain data consistency and prevent conflicts during concurrent execution.
Ready to test your Chapter IV: Process Synchronization knowledge?
Chapter IV: Process Synchronization
A short module quiz on process synchronization, mutual exclusion, semaphores, monitors, race conditions, and related problems.