详解Java中CountDownLatch异步转同步工具类详解Java中CountDownLatch异步转同

使用场景由于公司业务需求，需要对接socket、MQTT等消息队列。
众所周知 socket 是双向通信，socket的回复是人为定义的，客户端推送消息给服务端，服务端的回复是两条线。无法像http请求有回复。
下发指令给硬件时，需要校验此次数据下发是否成功。
用户体验而言，点击按钮就要知道此次的下发成功或失败。

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如上图模型，
第一种方案使用Tread.sleep
优点:占用资源小，放弃当前cpu资源
缺点: 回复速度快，休眠时间过长，仍然需要等待休眠结束才能返回，响应速度是固定的，无法及时响应第二种方案使用CountDownLatch

package com.lzy.demo.delay; import java.util.Map; import java.util.concurrent.ArrayBlockingQueue; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.CountDownLatch; import java.util.concurrent.DelayQueue; import java.util.concurrent.Delayed; import java.util.concurrent.ExecutorService; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; public class CountDownLatchPool {//countDonw池private final static Map countDownLatchMap = new ConcurrentHashMap<>(); //延迟队列private final static DelayQueue delayQueue = new DelayQueue<>(); private volatile static boolean flag =false; //单线程池private final static ExecutorService t = new ThreadPoolExecutor(1, 1,0L, TimeUnit.MILLISECONDS,new ArrayBlockingQueue<>(1)); public static void addCountDownLatch(Integer messageId) {CountDownLatch countDownLatch = countDownLatchMap.putIfAbsent(messageId,new CountDownLatch(1) ); if(countDownLatch == null){countDownLatch = countDownLatchMap.get(messageId); }try {addDelayQueue(messageId); countDownLatch.await(3L, TimeUnit.SECONDS); } catch (InterruptedException e) {e.printStackTrace(); }System.out.println("阻塞等待结束~~~~~~"); }public static void removeCountDownLatch(Integer messageId){CountDownLatch countDownLatch = countDownLatchMap.get(messageId); if(countDownLatch == null)return; countDownLatch.countDown(); countDownLatchMap.remove(messageId); System.out.println("清除Map数据"+countDownLatchMap); }private static void addDelayQueue(Integer messageId){delayQueue.add(new MessageDelayQueueUtil(messageId)); clearMessageId(); }private static void clearMessageId(){synchronized (CountDownLatchPool.class){if(flag){return; }flag = true; }t.execute(()->{while (delayQueue.size() > 0){System.out.println("进入线程并开始执行"); try {MessageDelayQueueUtil take = delayQueue.take(); Integer messageId1 = take.getMessageId(); removeCountDownLatch(messageId1); System.out.println("清除队列数据"+messageId1); } catch (InterruptedException e) {e.printStackTrace(); }}flag = false; System.out.println("结束end----"); }); }public static void main(String[] args) throws InterruptedException {/*测试超时清空mapnew Thread(()->addCountDownLatch(1)).start(); new Thread(()->addCountDownLatch(2)).start(); new Thread(()->addCountDownLatch(3)).start(); *///提前创建线程，清空countdownnew Thread(()->{try {Thread.sleep(500L); removeCountDownLatch(1); } catch (InterruptedException e) {e.printStackTrace(); }}).start(); //开始阻塞addCountDownLatch(1); //通过调整上面的sleep我们发现阻塞市场取决于countDownLatch.countDown()执行时间System.out.println("阻塞结束----"); }}class MessageDelayQueueUtil implements Delayed {private Integer messageId; private long avaibleTime; public Integer getMessageId() {return messageId; }public void setMessageId(Integer messageId) {this.messageId = messageId; }public long getAvaibleTime() {return avaibleTime; }public void setAvaibleTime(long avaibleTime) {this.avaibleTime = avaibleTime; }public MessageDelayQueueUtil(Integer messageId){this.messageId = messageId; //avaibleTime = 当前时间+ delayTime//重试3次，每次3秒+1秒的延迟this.avaibleTime=3000*3+1000 + System.currentTimeMillis(); }@Overridepublic long getDelay(TimeUnit unit) {long diffTime= avaibleTime- System.currentTimeMillis(); return unit.convert(diffTime,TimeUnit.MILLISECONDS); }@Overridepublic int compareTo(Delayed o) {//compareTo用在DelayedUser的排序return (int)(this.avaibleTime - ((MessageDelayQueueUtil) o).getAvaibleTime()); }}

由于socket并不确定每次都会有数据返回，所以map的数据会越来越大，最终导致内存溢出
需定时清除map内的无效数据。
可以使用DelayedQuene延迟队列来处理，相当于给对象添加一个过期时间
使用方法 addCountDownLatch 等待消息,异步回调消息清空removeCountDownLatch
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