一直被忽略的java 多线程并发工具类 CountDownLatch、Semaphore

CountDownLatch： 进行等待，知道发生指定数量事件后停止

构造方法:CountDownLatch(int num)
num是指锁存器而必须发生的事件次数。
主要方法：
await() : 当计数器（也就是上面的num）等于0时才结束等待
countDown(): 计数器（num)递减

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Semaphore： 实现经典信号量

构造方法：Semaphore(int num)
num是产生的信号量个数
主要方法：
acquire(): 获取一个信号量
release(): 释放一个信号量

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代码如下：

package com.test;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Semaphore;public class Question2 implements Runnable{    private String name;    private Semaphore sem;    private CountDownLatch downLatch;    public Question2(String name, Semaphore sem,CountDownLatch downLatch) {        super();        this.name = name;        this.sem = sem;        this.downLatch = downLatch;    }    public void test(String name){        System.out.println(name + " in!");        try {            Thread.sleep(2 * 1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println(name + " out!");    }    public static void main(String[] args) throws InterruptedException {        // TODO Auto-generated method stub        int thread_num = 10;        ExecutorService executorService = Executors.newCachedThreadPool();        Semaphore sem = new Semaphore(1); //每次产生信号量个数        CountDownLatch downLatch = new CountDownLatch(5); //初始化同步器        for(int i=0; i< thread_num;i++){            executorService.execute(new Question2("test "+i, sem,downLatch));        }        downLatch.await();        executorService.shutdown();    }    @Override    public void run() {        // TODO Auto-generated method stub        try {            sem.acquire();            this.test(this.name);            sem.release();            downLatch.countDown();        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}