12. Mutex in Java

💡 A mutex (short for mutual exclusion) is a synchronization mechanism used to control access to a shared resource by multiple threads. A mutex allows only one thread to access a resource at any given time, preventing race conditions and ensuring data integrity.

1. What is a Mutex?

• A mutex is a locking mechanism that allows only one thread to own the lock at any given time.
• When a thread acquires a mutex, other threads trying to acquire the same mutex are blocked until the mutex is released.

2. How to Implement a Mutex in Java

In Java, the ReentrantLock class from the java.util.concurrent.locks package is often used as a mutex. It provides a way to implement mutual exclusion and is more flexible than synchronized blocks or methods.

Example Using ReentrantLock as a Mutex

import java.util.concurrent.locks.ReentrantLock;

public class MutexExample {
    private final ReentrantLock mutex = new ReentrantLock();
    private int sharedResource = 0;

    public void increment() {
        mutex.lock(); // Acquire the mutex
        try {
            sharedResource++; // Critical section
            System.out.println("Shared Resource: " + sharedResource);
        } finally {
            mutex.unlock(); // Ensure the mutex is released
        }
    }

    public static void main(String[] args) {
        MutexExample example = new MutexExample();

        // Create multiple threads
        Thread thread1 = new Thread(example::increment);
        Thread thread2 = new Thread(example::increment);
        Thread thread3 = new Thread(example::increment);

        // Start threads
        thread1.start();
        thread2.start();
        thread3.start();

        try {
            thread1.join();
            thread2.join();
            thread3.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

3. Key Points

• Locking and Unlocking: Always ensure that locks are released in a finally block to prevent deadlocks.
• Reentrancy: ReentrantLock allows the same thread to acquire the lock multiple times without blocking itself.
• Fairness: ReentrantLock can be configured for fairness, which ensures that threads acquire locks in the order they requested them.

4. Summary of Mutex

Feature	Description
Purpose	Control access to shared resources.
Blocking Behavior	Other threads are blocked until the mutex is released.
Implementation	Typically implemented using ReentrantLock.
Reentrancy	Allows the same thread to acquire the lock multiple times.
Fairness	Can be configured to ensure FIFO access to threads.

Using mutexes is essential in multi-threaded applications to prevent race conditions and ensure data consistency. Let me know if you have further questions or need more details!