Java并发信号量demo

个人觉得信号量Semaphore  防止代码一次超过多个线程进入，在线程之间发送信号，下面代码是拷贝别的网站的demo。

import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Semaphore;public class TestSemaphore {public static void main(String[] args) {// 线程池ExecutorService exec = Executors.newCachedThreadPool();// 只能5个线程同时访问final Semaphore semp = new Semaphore(5);// 模拟20个客户端访问for (int index = 0; index < 20; index++) {final int NO = index;Runnable run = new Runnable() {public void run() {try {// 获取许可semp.acquire();System.out.println("Accessing: " + NO);Thread.sleep((long) (Math.random() * 10000));// 访问完后，释放semp.release();System.out.println("-----------------" + semp.availablePermits());} catch (InterruptedException e) {e.printStackTrace();}}};exec.execute(run);}// 退出线程池exec.shutdown();}}