Synchronization

1. What is Synchronization?

Synchronization is a mechanism that ensures only one thread can access a particular block of code or resource at a time, preventing multiple threads from causing conflicting changes to shared data simultaneously.

2. Why is it used?

When multiple threads access and modify the same shared data (like a bank account balance) at the same time, it can lead to incorrect or corrupted results. Synchronization prevents this by allowing only one thread in at a time.

3. Real-Life Example

Think of a single-occupancy washroom with a lock. Only one person can go inside and lock the door at a time; others must wait outside until it's free. Synchronization enforces this same "one at a time" access to shared resources.

4. Syntax

java
synchronized void methodName() {
    // only one thread can execute this at a time
}

5. Example Program

java
class Counter {
    int count = 0;

    synchronized void increment() {
        count++;
    }
}

public class SynchronizationDemo {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        Runnable task = () -> {
            for (int i = 0; i < 1000; i++) counter.increment();
        };

        Thread t1 = new Thread(task);
        Thread t2 = new Thread(task);
        t1.start();
        t2.start();
        t1.join();
        t2.join();

        System.out.println("Final count: " + counter.count);
    }
}

Output:

Final count: 2000

6. Key Points to Remember

• The synchronized keyword can be applied to methods or specific blocks of code.
• Synchronization prevents data corruption but can slow down a program if overused, since threads must wait their turn.
• Without synchronization, shared data updated by multiple threads can produce unpredictable, incorrect results.