详解Java中CountDownLatch异步转同步工具类
作者：lingzhi_ying
今天给大家带来的是关于Java的相关知识,文章围绕着CountDownLatch异步转同步工具类展开,文中有非常详细的介绍及代码示例,需要的朋友可以参考下
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。
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<Integer, CountDownLatch> countDownLatchMap = new ConcurrentHashMap<>();
//延迟队列
private final static DelayQueue<MessageDelayQueueUtil> 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map
new Thread(()->addCountDownLatch(1)).start();
new Thread(()->addCountDownLatch(2)).start();
new Thread(()->addCountDownLatch(3)).start();
*/
//提前创建线程，清空countdown
new 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();
}
@Override
public long getDelay(TimeUnit unit) {
long diffTime= avaibleTime- System.currentTimeMillis();
return unit.convert(diffTime,TimeUnit.MILLISECONDS);
}
@Override
public 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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