前言

前面我们讲了《nacos源码分析-服务注册(客户端)》 和 《nacos源码分析-服务注册(服务端)》，主要是讲的服务注册流程，本章节我们来讲服务心跳检测机制。

心跳续约客户端

其实我们在讲 nacos服务注册客户端的时候顺带就说了心跳，服务注册流程是：

nacos客户端服务心跳在服务注册的流程中触发，这里我再贴一下源码， NacosNamingService#registerInstance的源码：

public void registerInstance(String serviceName, String groupName, Instance instance) throws NacosException {
        if (instance.isEphemeral()) {
            BeatInfo beatInfo = new BeatInfo();
            beatInfo.setServiceName(NamingUtils.getGroupedName(serviceName, groupName));
            beatInfo.setIp(instance.getIp());
            beatInfo.setPort(instance.getPort());
            beatInfo.setCluster(instance.getClusterName());
            beatInfo.setWeight(instance.getWeight());
            beatInfo.setMetadata(instance.getMetadata());
            beatInfo.setScheduled(false);
            beatInfo.setPeriod(instance.getInstanceHeartBeatInterval());
            
            //添加心跳
            this.beatReactor.addBeatInfo(NamingUtils.getGroupedName(serviceName, groupName), beatInfo);
        }

        this.serverProxy.registerService(NamingUtils.getGroupedName(serviceName, groupName), groupName, instance);
    }

这里就看的比较清楚了，这里会把服务的ip，端口，服务名等信息封装到 BeatInfo 对象中，beatReactor.addBeatInfo是把当前服务实例加入心跳机制（心跳续约），然后通过serverProxy.registerService注册

代码在 BeatReactor#addBeatInfo中添加的心跳续约，在 NacosNamingService#registerInstance方法中把服务信息封装为一个 BeatInfo ，然后加入this.beatReactor.addBeatInfo 心跳机制。我们来看一下心跳是如何做的，下面是beatReactor.addBeatInfo的源码

 public void addBeatInfo(String serviceName, BeatInfo beatInfo) {
        LogUtils.NAMING_LOGGER.info("[BEAT] adding beat: {} to beat map.", beatInfo);
        String key = this.buildKey(serviceName, beatInfo.getIp(), beatInfo.getPort());
        BeatInfo existBeat = null;
        if ((existBeat = (BeatInfo)this.dom2Beat.remove(key)) != null) {
            existBeat.setStopped(true);
        }

        this.dom2Beat.put(key, beatInfo);
        //线程池，定时任务，5000毫秒发送一次心跳。beatInfo.getPeriod()是定时任务执行的频率
        this.executorService.schedule(new BeatTask(beatInfo), beatInfo.getPeriod(), TimeUnit.MILLISECONDS);
        MetricsMonitor.getDom2BeatSizeMonitor().set((double)this.dom2Beat.size());
    }

   //心跳任务
   class BeatTask implements Runnable {
        BeatInfo beatInfo;

        public BeatTask(BeatInfo beatInfo) {
            this.beatInfo = beatInfo;
        }

       public void run() {
            if (!this.beatInfo.isStopped()) {
            
                long nextTime = this.beatInfo.getPeriod();

                try {
                //发送心跳请求，拿到结果
                    JSONObject result = BeatReactor.this.serverProxy.sendBeat(this.beatInfo, BeatReactor.this.lightBeatEnabled);
                    long interval = (long)result.getIntValue("clientBeatInterval");
                    boolean lightBeatEnabled = false;
                    if (result.containsKey("lightBeatEnabled")) {
                        lightBeatEnabled = result.getBooleanValue("lightBeatEnabled");
                    }

                    BeatReactor.this.lightBeatEnabled = lightBeatEnabled;
                    if (interval > 0L) {
                        nextTime = interval;
                    }

                    int code = 10200;
                    if (result.containsKey("code")) {
                        code = result.getIntValue("code");
                    }

                    if (code == 20404) {
                    //实例不存在就创建
                        Instance instance = new Instance();
                        instance.setPort(this.beatInfo.getPort());
                        instance.setIp(this.beatInfo.getIp());
                        instance.setWeight(this.beatInfo.getWeight());
                        instance.setMetadata(this.beatInfo.getMetadata());
                        instance.setClusterName(this.beatInfo.getCluster());
                        instance.setServiceName(this.beatInfo.getServiceName());
                        instance.setInstanceId(instance.getInstanceId());
                        instance.setEphemeral(true);

                        try {
                            //注册服务
                            BeatReactor.this.serverProxy.registerService(this.beatInfo.getServiceName(), NamingUtils.getGroupName(this.beatInfo.getServiceName()), instance);
                        } catch (Exception var10) {
                        }
                    }
                } catch (NacosException var11) {
                    LogUtils.NAMING_LOGGER.error("[CLIENT-BEAT] failed to send beat: {}, code: {}, msg: {}", new Object[]{JSON.toJSONString(this.beatInfo), var11.getErrCode(), var11.getErrMsg()});
                }

                //定时任务：5s一次执行心跳任务
                BeatReactor.this.executorService.schedule(BeatReactor.this.new BeatTask(this.beatInfo), nextTime, TimeUnit.MILLISECONDS);
            }
        }
   }

和Eureka一样，心跳也是通过线程池 ScheduledExecutorService 来实现的，时间频率默认是5秒一次。

• BeatInfo : 心跳续约的对象，其中包括服务的IP，端口，服务名，权重等
• executorService.schedule ：定时任务，beatInfo.getPeriod()是定时任务执行频率，默认是5000 毫秒发送一次心跳续约请求到NacosServer
• BeatTask ：是一个Runnable线程，run方法中会调用 BeatReactor.this.serverProxy.sendBeat 发送心跳请求。

BeatTask作为心跳续约的线程对象，他的run方法中 通过 BeatReactor.this.serverProxy.sendBeat发送心跳，如果发现服务未注册会通过 BeatReactor.this.serverProxy.registerService 注册服务。

下面是 com.alibaba.nacos.client.naming.net.NamingProxy#sendBeat 发送心跳的方法

 public JSONObject sendBeat(BeatInfo beatInfo, boolean lightBeatEnabled) throws NacosException {
        if (LogUtils.NAMING_LOGGER.isDebugEnabled()) {
            LogUtils.NAMING_LOGGER.debug("[BEAT] {} sending beat to server: {}", this.namespaceId, beatInfo.toString());
        }

        Map<String, String> params = new HashMap(8);
        String body = "";
        if (!lightBeatEnabled) {
            try {
                body = "beat=" + URLEncoder.encode(JSON.toJSONString(beatInfo), "UTF-8");
            } catch (UnsupportedEncodingException var6) {
                throw new NacosException(500, "encode beatInfo error", var6);
            }
        }

        params.put("namespaceId", this.namespaceId);
        params.put("serviceName", beatInfo.getServiceName());
        params.put("clusterName", beatInfo.getCluster());
        params.put("ip", beatInfo.getIp());
        params.put("port", String.valueOf(beatInfo.getPort()));
        String result = this.reqAPI(UtilAndComs.NACOS_URL_BASE + "/instance/beat", params, body, "PUT");
        return JSON.parseObject(result);
    }

这里也是会拼接好心跳的地址 ：127.0.0.1:8848/nacos/v1/ns/instance/beat ,参数包括namespaceId命名空间ID；serviceName 服务名；clusterName 集群名；ip 服务的IP；port 端口。然后发送一个PUT请求。底层依然是从多个NacosServer随机选择一个发起心跳请求。底层交给httpClient去执行

心跳续约服务端

服务端还是在InstanceController中，其中提供了一个beat方法，我们出了要考虑他是如何处理心跳请求外，还要考虑他是如何做心跳过期检查的。源码如下

 /**
     * Create a beat for instance.
     * 心跳检测
     * @param request http request
     * @return detail information of instance
     * @throws Exception any error during handle
     */
    @CanDistro
    @PutMapping("/beat")
    @Secured(parser = NamingResourceParser.class, action = ActionTypes.WRITE)
    public ObjectNode beat(HttpServletRequest request) throws Exception {
        //客户端心跳频率 5s/次
         ObjectNode result = JacksonUtils.createEmptyJsonNode();
        result.put(SwitchEntry.CLIENT_BEAT_INTERVAL, switchDomain.getClientBeatInterval());
        //拿到请求中的beat数据，转成clientBeat对象
        String beat = WebUtils.optional(request, "beat", StringUtils.EMPTY);
        RsInfo clientBeat = null;
        if (StringUtils.isNotBlank(beat)) {
            clientBeat = JacksonUtils.toObj(beat, RsInfo.class);
        }//集群名
        String clusterName = WebUtils
                .optional(request, CommonParams.CLUSTER_NAME, UtilsAndCommons.DEFAULT_CLUSTER_NAME);
        //拿到客户端IP，端口
        String ip = WebUtils.optional(request, "ip", StringUtils.EMPTY);
        int port = Integer.parseInt(WebUtils.optional(request, "port", "0"));
        if (clientBeat != null) {
            if (StringUtils.isNotBlank(clientBeat.getCluster())) {
                clusterName = clientBeat.getCluster();
            } else {
                // fix #2533
                clientBeat.setCluster(clusterName);
            }
            ip = clientBeat.getIp();
            port = clientBeat.getPort();
        }
        //拿到命名空间ID和服务名
        String namespaceId = WebUtils.optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID);
        String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME);
        //检查服务名
        NamingUtils.checkServiceNameFormat(serviceName);
        Loggers.SRV_LOG.debug("[CLIENT-BEAT] full arguments: beat: {}, serviceName: {}", clientBeat, serviceName);
        //拿到服务表中的服务实例
        Instance instance = serviceManager.getInstance(namespaceId, serviceName, clusterName, ip, port);
        // 如果获取失败，说明心跳失败，实例尚未注册
        if (instance == null) {
            if (clientBeat == null) {//如果客户端心跳出现为空(请求参数中没beat)，返回资源没找到
                result.put(CommonParams.CODE, NamingResponseCode.RESOURCE_NOT_FOUND);
                return result;
            }
            
            Loggers.SRV_LOG.warn("[CLIENT-BEAT] The instance has been removed for health mechanism, "
                    + "perform data compensation operations, beat: {}, serviceName: {}", clientBeat, serviceName);
            //创建一个实例
            instance = new Instance();
            instance.setPort(clientBeat.getPort());
            instance.setIp(clientBeat.getIp());
            instance.setWeight(clientBeat.getWeight());
            instance.setMetadata(clientBeat.getMetadata());
            instance.setClusterName(clusterName);
            instance.setServiceName(serviceName);
            instance.setInstanceId(instance.getInstanceId());
            instance.setEphemeral(clientBeat.isEphemeral());
            //注册实例
            serviceManager.registerInstance(namespaceId, serviceName, instance);
        }
        //获取服务
        Service service = serviceManager.getService(namespaceId, serviceName);
        
        if (service == null) {
            //服务为空
            throw new NacosException(NacosException.SERVER_ERROR,
                    "service not found: " + serviceName + "@" + namespaceId);
        }
        if (clientBeat == null) {
            clientBeat = new RsInfo();
            clientBeat.setIp(ip);
            clientBeat.setPort(port);
            clientBeat.setCluster(clusterName);
        }
        //处理心跳请求
        service.processClientBeat(clientBeat);
        
        result.put(CommonParams.CODE, NamingResponseCode.OK);
        if (instance.containsMetadata(PreservedMetadataKeys.HEART_BEAT_INTERVAL)) {
            result.put(SwitchEntry.CLIENT_BEAT_INTERVAL, instance.getInstanceHeartBeatInterval());
        }
        result.put(SwitchEntry.LIGHT_BEAT_ENABLED, switchDomain.isLightBeatEnabled());
        return result;
    }

方法大致逻辑如下

• 拿到心跳请求参数，beat,其中包括客户端服务的IP，端口，服务名，命名空间等
• 通过serviceManager 从服务端服务注册表中拿到当前心跳请求的服务实例
• 如果实例为空会创建新的instance,通过serviceManager注册实例
• 然后拿到当前服务的service对象，调用 service.processClientBeat 方法处理心跳
• 最后返回OK
  

下面是 service#processClientBeat方法源码

public void processClientBeat(final RsInfo rsInfo) {
        //心跳处理器，runnable对象
        ClientBeatProcessor clientBeatProcessor = new ClientBeatProcessor();
        clientBeatProcessor.setService(this);
        clientBeatProcessor.setRsInfo(rsInfo);
        //这里HealthCheckReactor.scheduleNow(clientBeatProcessor);
        // 开启一个没有延迟的任务，可以理解为这里就是开启了一个异步线程处理心跳续约逻辑
        HealthCheckReactor.scheduleNow(clientBeatProcessor);
    }
    
 /**	没有延迟的任务
     * Schedule client beat check task without a delay.
     *
     * @param task health check task
     * @return scheduled future
     */
    public static ScheduledFuture<?> scheduleNow(Runnable task) {
        return GlobalExecutor.scheduleNamingHealth(task, 0, TimeUnit.MILLISECONDS);
    }

看得出来，心跳是通过 ClientBeatProcessor去处理的。通过定时任务去执行。ClientBeatProcessor是一个线程对象

public class ClientBeatProcessor implements Runnable {
    
    public static final long CLIENT_BEAT_TIMEOUT = TimeUnit.SECONDS.toMillis(15);
    
    private RsInfo rsInfo;
    
    private Service service;
    
    @JsonIgnore
    public PushService getPushService() {
        return ApplicationUtils.getBean(PushService.class);
    }
    
    public RsInfo getRsInfo() {
        return rsInfo;
    }
    
    public void setRsInfo(RsInfo rsInfo) {
        this.rsInfo = rsInfo;
    }
    
    public Service getService() {
        return service;
    }
    
    public void setService(Service service) {
        this.service = service;
    }
    
    @Override
    public void run() {
        //拿到续约的服务
        Service service = this.service;
        if (Loggers.EVT_LOG.isDebugEnabled()) {
            Loggers.EVT_LOG.debug("[CLIENT-BEAT] processing beat: {}", rsInfo.toString());
        }
        //拿到ip,端口，集群名等
        String ip = rsInfo.getIp();
        String clusterName = rsInfo.getCluster();
        int port = rsInfo.getPort();
        //拿到服务中的cLuster对象
        Cluster cluster = service.getClusterMap().get(clusterName);
        //拿到所有实例
        List<Instance> instances = cluster.allIPs(true);
        
        for (Instance instance : instances) {
            //找到当前发送心跳的instance,通过IP和端口对比
            if (instance.getIp().equals(ip) && instance.getPort() == port) {
                if (Loggers.EVT_LOG.isDebugEnabled()) {
                    Loggers.EVT_LOG.debug("[CLIENT-BEAT] refresh beat: {}", rsInfo.toString());
                }
                //设置心跳最后发送时间【重要】
                instance.setLastBeat(System.currentTimeMillis());
                if (!instance.isMarked() && !instance.isHealthy()) {
                    //设置健康状态为true
                    instance.setHealthy(true);
                    Loggers.EVT_LOG
                            .info("service: {} {POS} {IP-ENABLED} valid: {}:{}@{}, region: {}, msg: client beat ok",
                                    cluster.getService().getName(), ip, port, cluster.getName(),
                                    UtilsAndCommons.LOCALHOST_SITE);
                    //发布一个改变事件：ServiceChangeEvent
                    //PushService发布ServiceChangeEvent事件，使用udpPush推送给所有的客户端
                    getPushService().serviceChanged(service);
                }
            }
        }
    }
}

方法中会从服务注册表中取出心跳续约对应的服务，然后设置最后心跳时间和健康状态。

• instance.setLastBeat(System.currentTimeMillis()); ：就是把最后续约时间修改为当前系统时间
• instance.setHealthy(true);：把健康状态设置为tue

心跳超时检测

Nacos中的实例分为临时实例和永久实例，临时实例会在心跳续约超时后被注册中心剔除，则不会。对于非临时实例（ephemeral=false)，Nacos会采用主动的健康检测，定时向实例发送请求，根据响应来判断实例健康状态。

上面只是心跳续约的处理流程，心跳过期检测入口在servieManager#registerInstance 注册服务方法中，会调用servieManager#putServiceAndInit(service)方法对service进行初始化，在该方法中调用Service#init方法来开启心跳检查，该方法是在服务注册成功之后就会被调用。

// servieManager#putServiceAndInit 服务初始化
private void putServiceAndInit(Service service) throws NacosException {
        putService(service);
        service = getService(service.getNamespaceId(), service.getName());
        //服务初始化，心跳检查入口
        service.init();
        consistencyService
                .listen(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), true), service);
        consistencyService
                .listen(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), false), service);
        Loggers.SRV_LOG.info("[NEW-SERVICE] {}", service.toJson());
    }

下面是service#init()方法

@JsonInclude(Include.NON_NULL)
public class Service extends com.alibaba.nacos.api.naming.pojo.Service implements Record, RecordListener<Instances> {

	public void init() {
        //心跳检查。对临时服务的初始化	
        HealthCheckReactor.scheduleCheck(clientBeatCheckTask);
        //遍历注册表，初始化集群
        for (Map.Entry<String, Cluster> entry : clusterMap.entrySet()) {
            entry.getValue().setService(this);
           //对永久实例初始化,调用Cluster.init()
            entry.getValue().init();
        }
    }

//定时心跳超时检查 5s一次
public static void scheduleCheck(ClientBeatCheckTask task) {
        futureMap.computeIfAbsent(task.taskKey(),
                k -> GlobalExecutor.scheduleNamingHealth(task, 5000, 5000, TimeUnit.MILLISECONDS));
    }

临时服务，心跳检查通过定时任务5s一次，通过 ClientBeatCheckTask 线程对象来完成，

//客户端心跳检查
public class ClientBeatCheckTask implements Runnable {
   
    @Override
    public void run() {
        try {
            if (!getDistroMapper().responsible(service.getName())) {
                return;
            }
            
            if (!getSwitchDomain().isHealthCheckEnabled()) {
                return;
            }
            //拿到注册表中的所有实例
            List<Instance> instances = service.allIPs(true);
            
            // first set health status of instances:
            for (Instance instance : instances) {
                //判断心跳是否超时：系统时间 - 最后心跳时间 > 超时时间
                if (System.currentTimeMillis() - instance.getLastBeat() > instance.getInstanceHeartBeatTimeOut()) {
                    if (!instance.isMarked()) {
                        //如果是健康的，设置为不健康
                        if (instance.isHealthy()) {
                            instance.setHealthy(false);
                            Loggers.EVT_LOG
                                    .info("{POS} {IP-DISABLED} valid: {}:{}@{}@{}, region: {}, msg: client timeout after {}, last beat: {}",
                                            instance.getIp(), instance.getPort(), instance.getClusterName(),
                                            service.getName(), UtilsAndCommons.LOCALHOST_SITE,
                                            instance.getInstanceHeartBeatTimeOut(), instance.getLastBeat());
                            //抛出服务改变时间
                            getPushService().serviceChanged(service);
                            //抛出服务超时事件
                            ApplicationUtils.publishEvent(new InstanceHeartbeatTimeoutEvent(this, instance));
                        }
                    }
                }
            }
            
            if (!getGlobalConfig().isExpireInstance()) {
                return;
            }
            
            //移除过时的实例
            // then remove obsolete instances:
            for (Instance instance : instances) {
                //是否超时的标记
                if (instance.isMarked()) {
                    continue;
                }
                //超时时间大于30s就要把服务剔除
                if (System.currentTimeMillis() - instance.getLastBeat() > instance.getIpDeleteTimeout()) {
                    // delete instance
                    Loggers.SRV_LOG.info("[AUTO-DELETE-IP] service: {}, ip: {}", service.getName(),
                            JacksonUtils.toJson(instance));
                    //剔除服务
                    deleteIp(instance);
                }
            }
            
        } catch (Exception e) {
            Loggers.SRV_LOG.warn("Exception while processing client beat time out.", e);
        }
        
    }
    

方法做如下几个事情

• 拿到注册表中所有的服务实例
• 使用算法: 系统时间 - 最后心跳时间 > 超时时间 。来判断是否心跳超时，心跳超时默认是15s
• 超时的实例会设置健康状态为false,然后抛出服务改变事件ServiceChangeEvent和抛出心跳超时事件InstanceHeartbeatTimeoutEvent.也就是说你通过nacos的控制台看到服务的健康状态是false
• 最后还会判断如果超时时间超过 30s ，会删除当前服务

对于serviceChanged 服务改变事件的话是通过：PushService#serviceChanged来发布的，他会采用 udpPush 协议push给所有的客户端，当前服务状态。

永久实例的检查

下面是 com.alibaba.nacos.naming.core.Cluster#init 方法源码

   public synchronized void init() {
        if (inited) {
            return;
        }
        checkTask = new HealthCheckTask(this);
        //开启对 永久实例的 定时健康检测
        HealthCheckReactor.scheduleCheck(checkTask);
        inited = true;
    }
    
	public static ScheduledFuture<?> scheduleCheck(HealthCheckTask task) {
        task.setStartTime(System.currentTimeMillis());
        //开启定时任务心跳检查
        return GlobalExecutor.scheduleNamingHealth(task, task.getCheckRtNormalized(), TimeUnit.MILLISECONDS);
    }

这里通过HealthCheckTask来处理永久实例的健康检查，通过定时任务定时检查。下面是 HealthCheckTask源码

//这里在计算定时任务的时间频率
private void initCheckRT() {
        // first check time delay 计算主动检测的时间频率
        //周期为2000 + 5000毫秒内的随机数
        checkRtNormalized =
                2000 + RandomUtils.nextInt(0, RandomUtils.nextInt(0, switchDomain.getTcpHealthParams().getMax()));
        checkRtBest = Long.MAX_VALUE;
        checkRtWorst = 0L;
    }
    
    @Override
    public void run() {
        
        try {
            if (distroMapper.responsible(cluster.getService().getName()) && switchDomain
                    .isHealthCheckEnabled(cluster.getService().getName())) {
                    //执行检查逻辑，使用的是 TcpSuperSenseProcessor 处理，基于TCP模式
                healthCheckProcessor.process(this);
                if (Loggers.EVT_LOG.isDebugEnabled()) {
                    Loggers.EVT_LOG
                            .debug("[HEALTH-CHECK] schedule health check task: {}", cluster.getService().getName());
                }
            }
        } catch (Throwable e) {
            Loggers.SRV_LOG
                    .error("[HEALTH-CHECK] error while process health check for {}:{}", cluster.getService().getName(),
                            cluster.getName(), e);
        } finally {
            ...
        }
    }

代码 healthCheckProcessor.process(this); 是处理心跳检查，使用的是实现类 TcpSuperSenseProcessor ，他是一个Runnable，源码如下

@Override
   public void process(HealthCheckTask task) {
   	//拿到集群中的所有实例，非临时ephemeral=false的实例
       List<Instance> ips = task.getCluster().allIPs(false);
       
       if (CollectionUtils.isEmpty(ips)) {
           return;
       }
       
       for (Instance ip : ips) {
           
           ...
           Beat beat = new Beat(ip, task);
           //添加到队列LinkedBlockingQueue，可以看到，所有的健康检测任务都被放入一个阻塞队列
           taskQueue.add(beat);
           MetricsMonitor.getTcpHealthCheckMonitor().incrementAndGet();
       }
   }

//处理任务
	private void processTask() throws Exception {
        Collection<Callable<Void>> tasks = new LinkedList<>();
        do {
            Beat beat = taskQueue.poll(CONNECT_TIMEOUT_MS / 2, TimeUnit.MILLISECONDS);
            if (beat == null) {
                return;
            }
            //把任务封装到TaskProcessor
            tasks.add(new TaskProcessor(beat));
        } while (taskQueue.size() > 0 && tasks.size() < NIO_THREAD_COUNT * 64);
        //执行所有任务，批量执行
        for (Future<?> f : GlobalExecutor.invokeAllTcpSuperSenseTask(tasks)) {
            f.get();
        }
    }
    
    @Override
    public void run() {
    //循环，不停的从队列中拿到beat心跳任务去执行
        while (true) {
            try {
            //执行任务
                processTask();
                
                int readyCount = selector.selectNow();
                if (readyCount <= 0) {
                    continue;
                }
                
                Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
                while (iter.hasNext()) {
                    SelectionKey key = iter.next();
                    iter.remove();
                    
                    GlobalExecutor.executeTcpSuperSense(new PostProcessor(key));
                }
            } catch (Throwable e) {
                SRV_LOG.error("[HEALTH-CHECK] error while processing NIO task", e);
            }
        }
    }
    

看到这里我们大概明白，healthCheckProcessor通过TCP来向客户端发送心跳检查，底层通过队列LinkedBlockingQueue来存储心跳任务Beat 。 然后TcpSuperSenseProcessor 本身是一个Runnable，通过定时从队列中取出Beat任务，并封装陈 TaskProcessor批量执行。下面是 TaskProcessor源码

 private class TaskProcessor implements Callable<Void> {
        
        private static final int MAX_WAIT_TIME_MILLISECONDS = 500;
        
        Beat beat;
        
        public TaskProcessor(Beat beat) {
            this.beat = beat;
        }
        
        @Override
        public Void call() {
            long waited = System.currentTimeMillis() - beat.getStartTime();
            if (waited > MAX_WAIT_TIME_MILLISECONDS) {
                Loggers.SRV_LOG.warn("beat task waited too long: " + waited + "ms");
            }
            
            SocketChannel channel = null;
            try {
                Instance instance = beat.getIp();
                
                BeatKey beatKey = keyMap.get(beat.toString());
                if (beatKey != null && beatKey.key.isValid()) {
                    if (System.currentTimeMillis() - beatKey.birthTime < TCP_KEEP_ALIVE_MILLIS) {
                        instance.setBeingChecked(false);
                        return null;
                    }
                    
                    beatKey.key.cancel();
                    beatKey.key.channel().close();
                }
                
                channel = SocketChannel.open();
                channel.configureBlocking(false);
                // only by setting this can we make the socket close event asynchronous
                channel.socket().setSoLinger(false, -1);
                channel.socket().setReuseAddress(true);
                channel.socket().setKeepAlive(true);
                channel.socket().setTcpNoDelay(true);
                
                Cluster cluster = beat.getTask().getCluster();
                int port = cluster.isUseIPPort4Check() ? instance.getPort() : cluster.getDefCkport();
                channel.connect(new InetSocketAddress(instance.getIp(), port));
                
                SelectionKey key = channel.register(selector, SelectionKey.OP_CONNECT | SelectionKey.OP_READ);
                key.attach(beat);
                keyMap.put(beat.toString(), new BeatKey(key));
                
                beat.setStartTime(System.currentTimeMillis());
                
                GlobalExecutor
                        .scheduleTcpSuperSenseTask(new TimeOutTask(key), CONNECT_TIMEOUT_MS, TimeUnit.MILLISECONDS);
            } catch (Exception e) {
                beat.finishCheck(false, false, switchDomain.getTcpHealthParams().getMax(),
                        "tcp:error:" + e.getMessage());
                
                if (channel != null) {
                    try {
                        channel.close();
                    } catch (Exception ignore) {
                    }
                }
            }
            
            return null;
        }
    }

看得出来他是一个 Callable，通过 NIO去发送TCP请求。这里做个小总结

Nacos的健康检测分为临时实例和永久实例两种：

• 对于临时实例：客户端5秒发送一次心跳，超过15秒则标记为不健康，超时30秒则从服务列表删除
• 对于永久实例：服务端主动健康检测，周期为2000 + 5000毫秒内的随机数，检测超时只会标记为不健康，不会删除

好了文章到此结束，用一个图来总结一下服务注册和心跳

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