In a world where multiple threads or processes run concurrently, synchronization is the key to ensuring correct and predictable behavior. Whether it's threads updating shared data or processes coordinating access to system resources, synchronization prevents race conditions, maintains data integrity, and avoids chaos.
🧠 What is Synchronization?
✅ Definition:
Synchronization is the coordination of concurrent processes or threads to ensure correct sequencing of operations and controlled access to shared resources.
It ensures that only one thread/process accesses critical data at a time, avoiding data corruption and logical errors.
💡 Real-Life Analogy
Imagine multiple people trying to write on a whiteboard. If they write at the same time without coordination, the content gets jumbled — this is like a race condition. Synchronization is like using a token or turn-based system, ensuring only one person writes at a time.
📌 Why Synchronization is Needed
1. To Prevent Race Conditions
Occurs when multiple threads modify shared data without proper synchronization.
2. To Avoid Inconsistent States
Uncoordinated access may leave shared objects in an invalid state.
3. To Maintain Order
Some operations must occur in a specific sequence (e.g., initializing before using a variable).
⚙️ Types of Synchronization
| Type | Description |
|---|---|
| Process Synchronization | Ensures proper sequence and coordination among processes. |
| Thread Synchronization | Ensures threads in a process work without interfering with each other. |
🧱 Critical Section Problem
A critical section is a part of a program where shared resources are accessed or modified.
🔐 Conditions for Correct Synchronization (for critical sections):
- Mutual Exclusion – Only one process/thread is in the critical section at a time.
- Progress – If no process is in the critical section, one of the waiting processes must enter.
- Bounded Waiting – Each process must have a limit on how long it waits to enter the section.
🛠️ Synchronization Mechanisms
| Mechanism | Description |
|---|---|
| Mutex (Mutual Exclusion Lock) | Allows only one thread to access a critical section at a time. |
| Semaphore | A variable used to control access to a resource. Can be binary or counting. |
| Spinlock | A lock where a thread waits in a loop (spins) while checking for availability. |
| Monitor | A high-level synchronization construct that provides automatic locking. |
| Atomic Variables / Instructions | Operations on shared variables that execute as a single, indivisible unit. |
| Condition Variables | Used to block a thread until a condition is true. Usually paired with mutexes. |
🔄 Mutex vs Semaphore (Quick Comparison)
| Feature | Mutex | Semaphore |
|---|---|---|
| Resource Count | 1 (binary lock) | 1 or more (can count multiple) |
| Ownership | Only owner can unlock | Anyone can signal (release) |
| Use Case | Exclusive access | Signaling between threads/processes |