Semaphore

信号量主要用于两个目的：

1.用于多个共享资源的互斥使用

2.用于并发数的控制.

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class SemaphoreDemo {
    public static void main(String[] args) {
        Semaphore semaphore = new Semaphore(3);
        for (int i = 0; i <= 6; i++) {
            new Thread(() -> {

                System.out.println(Thread.currentThread().getName() + "	 抢到车位");
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName());
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "	 停车三秒后离开车位");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            }, String.valueOf(i)).start();
        }
    }
}