Semaphore应用

场景

桥只能允许两个人，多一个人上桥就会落水，所以只能保证桥上的人流量为2人。

实现

public class SemaphoreTest {

    private static final Semaphore semaphore = new Semaphore(2);
    
    public static void main(String[] args) {
        ThreadPoolExecutor tpe = new ThreadPoolExecutor(2, 
                2, 
                20, 
                TimeUnit.SECONDS, 
                new ArrayBlockingQueue<Runnable>(10));
        
        tpe.allowCoreThreadTimeOut(true);
        
        tpe.execute(new Runnable() {

            @Override
            public void run() {
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + " 上桥");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        
        tpe.execute(new Runnable() {

            @Override
            public void run() {
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + " 上桥");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        
        tpe.execute(new Runnable() {

            @Override
            public void run() {
                try {
                    semaphore.release();
                    System.out.println(Thread.currentThread().getName() + " 下桥");
                    
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + " 上桥");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

结果：

pool-1-thread-1 上桥
pool-1-thread-2 上桥
pool-1-thread-1 下桥
pool-1-thread-1 上桥