上一篇【第35篇】Netty时间轮HashedWheelTimer源码解析——百万定时任务的秘密下一篇【第37篇】Netty流量整形——优雅控制客户端发送速率一、场景一延迟消息队列publicclassDelayMessageQueue{privatefinalHashedWheelTimertimernewHashedWheelTimer();privatefinalMapString,TimeoutpendingnewConcurrentHashMap();// 发送延迟消息publicvoidsendDelayed(StringmsgId,Stringcontent,longdelayMs){Timeouttimeouttimer.newTimeout(t-{pending.remove(msgId);System.out.println(延迟消息到达: idmsgId, contentcontent);processMessage(content);},delayMs,TimeUnit.MILLISECONDS);pending.put(msgId,timeout);}// 取消延迟消息publicvoidcancelDelayed(StringmsgId){Timeouttimeoutpending.remove(msgId);if(timeout!null)timeout.cancel();}}二、场景二超时重试publicclassTimeoutRetryHandler{privatefinalHashedWheelTimertimernewHashedWheelTimer();publicFuture?sendWithRetry(Channelchannel,Objectmsg,intmaxRetries){PromiseBooleanpromisechannel.eventLoop().newPromise();doSend(channel,msg,promise,maxRetries,0);returnpromise;}privatevoiddoSend(Channelchannel,Objectmsg,PromiseBooleanpromise,intmaxRetries,intattempt){channel.writeAndFlush(msg).addListener(f-{if(f.isSuccess()){promise.setSuccess(true);}elseif(attemptmaxRetries){// 指数退避1s, 2s, 4s, 8s...longdelay(long)Math.pow(2,attempt)*1000;timer.newTimeout(t-doSend(channel,msg,promise,maxRetries,attempt1),delay,TimeUnit.MILLISECONDS);}else{promise.setFailure(f.cause());}});}}三、场景三连接心跳管理publicclassHeartbeatManager{privatefinalHashedWheelTimertimernewHashedWheelTimer();privatefinalMapChannel,TimeoutheartbeatsnewConcurrentHashMap();publicvoidstartHeartbeat(Channelchannel,longintervalMs){scheduleHeartbeat(channel,intervalMs);}privatevoidscheduleHeartbeat(Channelchannel,longintervalMs){Timeouttimeouttimer.newTimeout(t-{if(channel.isActive()){channel.writeAndFlush(newHeartbeatMsg());scheduleHeartbeat(channel,intervalMs);// 递归调度}},intervalMs,TimeUnit.MILLISECONDS);heartbeats.put(channel,timeout);}publicvoidstopHeartbeat(Channelchannel){Timeouttimeoutheartbeats.remove(channel);if(timeout!null)timeout.cancel();}}四、大规模定时任务层级时间轮设计单层时间轮8槽×100ms 800ms周期。如果需要1小时的定时任务就需要大量remainingRounds。层级时间轮多层时间轮每层精度不同。Layer 0: 256槽 × 1ms 256ms (毫秒级) Layer 1: 64槽 × 256ms 16.384s (秒级) Layer 2: 64槽 × 16s 1024s (分钟级) Layer 3: 64槽 × 17min 18小时 (小时级) 当Layer 0转满一轮Layer 1推进一格 当Layer 1转满一轮Layer 2推进一格五、总结场景实现方式优势延迟消息timer.newTimeout()O(1)插入超时重试递归调度指数退避自动重试心跳管理递归调度心跳任务无需线程池大规模任务层级时间轮亿级定时任务上一篇【第35篇】Netty时间轮HashedWheelTimer源码解析——百万定时任务的秘密下一篇【第37篇】Netty流量整形——优雅控制客户端发送速率
