What are some examples of semaphore usage in programming?

What are some examples of semaphore usage in programming?

Semaphores are often used in concurrent programming to control access to shared resources. For example, in a multi-threaded application, a semaphore can limit the number of threads that access a particular resource at the same time.

Can you give me a specific programming language example?

Sure! In Java, you can use the Semaphore class from the java.util.concurrent package. 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 thread2 = new Thread(() -> accessResource());
        thread1.start();
        thread2.start();
    }

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

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

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