How do I use semaphores in Java?

How do I use semaphores in Java?

Semaphores in Java are used to control access to a shared resource by multiple threads. You can use the Semaphore class from the java.util.concurrent package. Would you like a code example?

Yes, please provide a code example.

Here's a simple example:

import java.util.concurrent.Semaphore;

public class SemaphoreExample {
    private static final Semaphore semaphore = new Semaphore(1);

    public static void main(String[] args) {
        Thread thread1 = new Thread(() -> accessResource("Thread 1"));
        Thread thread2 = new Thread(() -> accessResource("Thread 2"));

        thread1.start();
        thread2.start();
    }

    private static void accessResource(String threadName) {
        try {
            semaphore.acquire();
            System.out.println(threadName + " has acquired the semaphore.");
            // Simulate resource access
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println(threadName + " is releasing the semaphore.");
            semaphore.release();
        }
    }
}

This code demonstrates how two threads can access a shared resource using a semaphore.

What happens if a thread tries to acquire a semaphore that is already held?

If a thread tries to acquire a semaphore that is already held, it will block and wait until the semaphore is released by the thread that currently holds it. This ensures that only a limited number of threads can access the resource at the same time.