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
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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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原文链接：https://blog.csdn.net/qq_37256345/article/details/117808156
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