由于公司業務需求，需要對接socket、MQTT等消息隊列。眾所周知 socket 是雙向通信，socket的回復是人為定義的，客戶端推送消息給服務端，服務端的回復是兩條線。無法像http請求有回復。下發指令給硬件時，需要校驗此次數據下發是否成功。用戶體驗而言，點擊按鈕就要知道此次的下發成功或失敗。

如上圖模型，

第一種方案使用Tread.sleep優點:占用資源小，放棄當前cpu資源缺點: 回復速度快，休眠時間過長，仍然需要等待休眠結束才能返回，響應速度是固定的，無法及時響應第二種方案使用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<>(); //延遲隊列 private final static DelayQueue<MessageDelayQueueUtil> delayQueue = new DelayQueue<>(); private volatile static boolean flag =false; //單線程池 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('阻塞等待結束~~~~~~'); } 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數據'+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('進入線程并開始執行');try { MessageDelayQueueUtil take = delayQueue.take(); Integer messageId1 = take.getMessageId(); removeCountDownLatch(messageId1); System.out.println('清除隊列數據'+messageId1);} catch (InterruptedException e) { e.printStackTrace();} } flag = false; System.out.println('結束end----');}); } public static void main(String[] args) throws InterruptedException {/*測試超時清空mapnew Thread(()->addCountDownLatch(1)).start();new Thread(()->addCountDownLatch(2)).start();new Thread(()->addCountDownLatch(3)).start();*///提前創建線程，清空countdownnew Thread(()->{ try {Thread.sleep(500L);removeCountDownLatch(1); } catch (InterruptedException e) {e.printStackTrace(); }}).start();//開始阻塞addCountDownLatch(1); //通過調整上面的sleep我們發現阻塞市場取決于countDownLatch.countDown()執行時間 System.out.println('阻塞結束----'); }}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 = 當前時間+ delayTime//重試3次，每次3秒+1秒的延遲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并不確定每次都會有數據返回，所以map的數據會越來越大，最終導致內存溢出需定時清除map內的無效數據?？梢允褂肈elayedQuene延遲隊列來處理，相當于給對象添加一個過期時間

使用方法 addCountDownLatch 等待消息,異步回調消息清空removeCountDownLatch

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