semaphore

1.信号量：java.util.concurrent的一个工具类，可以设置参数，控制同时访问的个数；主要有方法acquire（），release（）获取和释放令牌；可以用于限流操作。

2、停车场demo

package com.ydlclass.collection;

import com.ydlclass.lock.ThreadUtil;

import java.util.Random;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

public class SemaphoreTest {
    public static void main(String[] args) {
        final Semaphore semaphore = new Semaphore(5);//定义信号量为5
        ExecutorService executorService = Executors.newCachedThreadPool();//可缓存的线程池,不限制线程的个数
        for (int i = 0; i < 100; i++) {
            Runnable task = () -> {
                try {
                    semaphore.acquire();//首先让线程拿到令牌
                    System.out.println("开进一辆车");
                    Thread.sleep(new Random().nextInt(15));//假设每辆车随机在停车场停留了一段时间
                    System.out.println("开出一辆车");
                    semaphore.release();
                } catch (InterruptedException e){
                    e.printStackTrace();
                }

            };
            executorService.execute(task);//执行线程池中task
        }
        executorService.shutdown();//关闭线程池



    }
}