import java.util.concurrent.*;

public class TestSemaphore {
    public static void main(String[] args) {
        int resources = 2;
        Semaphore semaphore = new Semaphore(resources);
        ExecutorService executor = Executors.newCachedThreadPool();
        for (int i = 1; i <= 10; i++) {
            final int num = i;
            executor.execute(() -> {
                try {
                    semaphore.acquire();
                    System.out.println("Thread " + num + " start.");
                    Thread.sleep(100);
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            });
        }
        executor.shutdown();
    }
}