What are some examples of semaphores in Java?

What are some examples of semaphores in Java?

Semaphores in Java are used to control access to a shared resource. For example, you can use a semaphore to limit the number of threads accessing a database connection pool.

Can you show me a code example of using a semaphore?

Sure! Here's a simple example:

import java.util.concurrent.Semaphore;

public class SemaphoreExample {
    private static final Semaphore semaphore = new Semaphore(2);

    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            new Thread(new Worker(i)).start();
        }
    }

    static class Worker implements Runnable {
        private int id;

        Worker(int id) {
            this.id = id;
        }

        public void run() {
            try {
                System.out.println("Worker " + id + " is waiting to acquire the semaphore.");
                semaphore.acquire();
                System.out.println("Worker " + id + " has acquired the semaphore.");
                // Simulate work
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                System.out.println("Worker " + id + " is releasing the semaphore.");
                semaphore.release();
            }
        }
    }
}

What happens if a thread tries to acquire a semaphore that is already at its limit?

If a thread tries to acquire a semaphore that has reached its limit, it will block and wait until another thread releases the semaphore.