Nacos源码—8.Nacos升级gRPC分析三

大纲

7.服务端对服务实例进行健康检查

8.服务下线如何注销注册表和客户端等信息

9.事件驱动架构源码分析

7.服务端对服务实例进行健康检查

(1)服务端对服务实例进行健康检查的设计逻辑

(2)服务端对服务实例进行健康检查的源码

(3)服务端检查服务实例不健康后的注销处理

(1)服务端对服务实例进行健康检查的设计逻辑

一.首先会获取所有客户端的Connection连接对象

Connection连接对象里有个属性叫lastActiveTime，表示的是最后存活时间。

二.然后判断当前时间-最后存活时间是否大于20s

如果大于，则把该Connection连接对象的connectionId放入到一个集合里。这个集合是一个名为outDatedConnections的待移除集合Set，此时该Connection连接对象并不会马上删除。

三.当判断完全部的Connection连接对象后会遍历outDatedConnections集合

向遍历到的Connection连接对象发起一次请求，确认是否真的下线。如果响应成功，则往successConnections集合中添加connectionId，并且刷新Connection连接对象的lastActiveTime属性。这个机制有一个专业的名称叫做：探活机制。

四.遍历待移除集合进行注销并且在注销之前先判断一下是否探活成功

也就是connectionId存在于待移除集合outDatedConnections中，但是不存在于探活成功集合successConnections中，那么这个connectionId对应的客户端就会被注销掉。

(2)服务端对服务实例进行健康检查的源码

对服务实例进行健康检查的源码入口是ConnectionManager的start()方法。

@Service
public class ConnectionManager extends Subscriber<ConnectionLimitRuleChangeEvent> {
    Map<String, Connection> connections = new ConcurrentHashMap<>();
    ...

    //Start Task：Expel the connection which active Time expire.
    @PostConstruct
    public void start() {
        //Start UnHealthy Connection Expel Task.
        RpcScheduledExecutor.COMMON_SERVER_EXECUTOR.scheduleWithFixedDelay(new Runnable() {
            @Override
            public void run() {
                ...
                //一.首先获取所有的连接
                Set<Map.Entry<String, Connection>> entries = connections.entrySet();
                ...
                //二.然后判断客户端是否超过20s没有发来心跳信息了，如果是则会将clientId加入outDatedConnections集合中
                Set<String> outDatedConnections = new HashSet<>();
                long now = System.currentTimeMillis();

                for (Map.Entry<String, Connection> entry : entries) {
                    Connection client = entry.getValue();
                    String clientIp = client.getMetaInfo().getClientIp();
                    AtomicInteger integer = expelForIp.get(clientIp);
                    if (integer != null && integer.intValue() > 0) {
                        integer.decrementAndGet();
                        expelClient.add(client.getMetaInfo().getConnectionId());
                        expelCount--;
                    } else if (now - client.getMetaInfo().getLastActiveTime() >= KEEP_ALIVE_TIME) {//判断心跳时间
                        //添加到待移除列表
                        outDatedConnections.add(client.getMetaInfo().getConnectionId());
                    }
                }
                ...
                //client active detection.
                //三.初次检测完超过20s的Connection连接对象后，并不会立马进行删除，而是进行探活，服务端主动请求客户端，来确认是否真的下线
                Loggers.REMOTE_DIGEST.info("Out dated connection ,size={}", outDatedConnections.size());
                if (CollectionUtils.isNotEmpty(outDatedConnections)) {
                    Set<String> successConnections = new HashSet<>();
                    final CountDownLatch latch = new CountDownLatch(outDatedConnections.size());
                    //遍历超过20s没有心跳的客户端clientId
                    for (String outDateConnectionId : outDatedConnections) {
                        try {
                            Connection connection = getConnection(outDateConnectionId);
                            if (connection != null) {
                                ClientDetectionRequest clientDetectionRequest = new ClientDetectionRequest();
                                //调用GrpcConnection.asyncRequest()方法异步发送请求
                                connection.asyncRequest(clientDetectionRequest, new RequestCallBack() {
                                    @Override
                                    public Executor getExecutor() {
                                        return null;
                                    }

                                    @Override
                                    public long getTimeout() {
                                        return 1000L;
                                    }

                                    @Override
                                    public void onResponse(Response response) {
                                        latch.countDown();
                                        if (response != null && response.isSuccess()) {
                                            //响应成功刷新心跳时间
                                            connection.freshActiveTime();
                                            //并且加入到探活成功的集合列表中
                                            successConnections.add(outDateConnectionId);
                                        }
                                    }

                                    @Override
                                    public void onException(Throwable e) {
                                        latch.countDown();
                                    }
                                });
                                Loggers.REMOTE_DIGEST.info("[{}]send connection active request ", outDateConnectionId);
                            } else {
                                latch.countDown();
                            }
                        } catch (ConnectionAlreadyClosedException e) {
                            latch.countDown();
                        } catch (Exception e) {
                            Loggers.REMOTE_DIGEST.error("[{}]Error occurs when check client active detection ,error={}", outDateConnectionId, e);
                            latch.countDown();
                        }
                    }

                    latch.await(3000L, TimeUnit.MILLISECONDS);
                    Loggers.REMOTE_DIGEST.info("Out dated connection check successCount={}", successConnections.size());
                    //经过探活还是不成功的Connection连接对象，就准备进行移除了
                    //遍历20s没有心跳的客户端，准备移除客户端信息
                    for (String outDateConnectionId : outDatedConnections) {
                        //判断探活是否成功，如果成功了则不需要移除
                        if (!successConnections.contains(outDateConnectionId)) {
                            Loggers.REMOTE_DIGEST.info("[{}]Unregister Out dated connection....", outDateConnectionId);
                            //执行客户端注销逻辑
                            unregister(outDateConnectionId);
                        }
                    }
                }
                ...
            }
        }, 1000L, 3000L, TimeUnit.MILLISECONDS);
    }
    ...
}

(3)服务端检查服务实例不健康后的注销处理

进行注销处理的方法是ConnectionManager的unregister()方法。该方法主要会移除Connection连接对象 + 清除一些数据，以及发布一个ClientDisconnectEvent客户端注销事件。

@Service
public class ConnectionManager extends Subscriber<ConnectionLimitRuleChangeEvent> {
    private Map<String, AtomicInteger> connectionForClientIp = new ConcurrentHashMap<String, AtomicInteger>(16);
    Map<String, Connection> connections = new ConcurrentHashMap<>();

    @Autowired
    private ClientConnectionEventListenerRegistry clientConnectionEventListenerRegistry;
    ...

    //unregister a connection .
    public synchronized void unregister(String connectionId) {
        //移除客户端信息
        Connection remove = this.connections.remove(connectionId);
        if (remove != null) {
            String clientIp = remove.getMetaInfo().clientIp;
            AtomicInteger atomicInteger = connectionForClientIp.get(clientIp);
            if (atomicInteger != null) {
                int count = atomicInteger.decrementAndGet();
                if (count <= 0) {
                    connectionForClientIp.remove(clientIp);
                }
            }
            remove.close();
            Loggers.REMOTE_DIGEST.info("[{}]Connection unregistered successfully. ", connectionId);
            //通知客户端注销连接
            clientConnectionEventListenerRegistry.notifyClientDisConnected(remove);
        }
    }
    ...
}

@Service
public class ClientConnectionEventListenerRegistry {
    ...
    //notify where a new client disconnected.
    public void notifyClientDisConnected(final Connection connection) {
        for (ClientConnectionEventListener clientConnectionEventListener : clientConnectionEventListeners) {
            try {
                //调用ConnectionBasedClientManager.clientDisConnected()方法
                clientConnectionEventListener.clientDisConnected(connection);
            } catch (Throwable throwable) {
                Loggers.REMOTE.info("[NotifyClientDisConnected] failed for listener {}", clientConnectionEventListener.getName(), throwable);
            }
        }
    }
    ...
}

@Component("connectionBasedClientManager")
public class ConnectionBasedClientManager extends ClientConnectionEventListener implements ClientManager {
    private final ConcurrentMap<String, ConnectionBasedClient> clients = new ConcurrentHashMap<>();
    ...

    @Override
    public boolean clientDisconnected(String clientId) {
        Loggers.SRV_LOG.info("Client connection {} disconnect, remove instances and subscribers", clientId);
        ConnectionBasedClient client = clients.remove(clientId);
        if (null == client) {
            return true;
        }
        client.release();
        //最后发布客户端注销事件
        NotifyCenter.publishEvent(new ClientEvent.ClientDisconnectEvent(client));
        return true;
    }
    ...
}

ClientDisconnectEvent客户端注销事件会被两个监听响应：一是ClientServiceIndexesManager的onEvent()方法用来移除注册表 + 订阅表信息，二是DistroClientDataProcessor的onEvent()方法用来同步服务实例被注销后的数据。

@Component
public class ClientServiceIndexesManager extends SmartSubscriber {
    //注册表(服务提供者)，一个Service服务对象，对应多个服务实例的clientId
    private final ConcurrentMap<Service, Set<String>> publisherIndexes = new ConcurrentHashMap<>();

    //订阅者列表(服务消费者)，一个Service服务对象，对应多个订阅者的clientId
    private final ConcurrentMap<Service, Set<String>> subscriberIndexes = new ConcurrentHashMap<>();
    ...

    @Override
    public void onEvent(Event event) {
        if (event instanceof ClientEvent.ClientDisconnectEvent) {
            handleClientDisconnect((ClientEvent.ClientDisconnectEvent) event);
        } else if (event instanceof ClientOperationEvent) {
            handleClientOperation((ClientOperationEvent) event);
        }
    }

    private void handleClientDisconnect(ClientEvent.ClientDisconnectEvent event) {
        Client client = event.getClient();
        for (Service each : client.getAllSubscribeService()) {
            //移除订阅者列表的元素
            removeSubscriberIndexes(each, client.getClientId());
        }
        for (Service each : client.getAllPublishedService()) {
            //移除注册表的元素
            removePublisherIndexes(each, client.getClientId());
        }
    }

    private void removePublisherIndexes(Service service, String clientId) {
        if (!publisherIndexes.containsKey(service)) {
            return;
        }
        publisherIndexes.get(service).remove(clientId);
        NotifyCenter.publishEvent(new ServiceEvent.ServiceChangedEvent(service, true));
    }

    private void removeSubscriberIndexes(Service service, String clientId) {
        if (!subscriberIndexes.containsKey(service)) {
            return;
        }
        subscriberIndexes.get(service).remove(clientId);
        if (subscriberIndexes.get(service).isEmpty()) {
            subscriberIndexes.remove(service);
        }
    }
    ...
}

public class DistroClientDataProcessor extends SmartSubscriber implements DistroDataStorage, DistroDataProcessor {
    ...
    @Override
    public void onEvent(Event event) {
        ...
        if (event instanceof ClientEvent.ClientVerifyFailedEvent) {
            syncToVerifyFailedServer((ClientEvent.ClientVerifyFailedEvent) event);
        } else {
            syncToAllServer((ClientEvent) event);
        }
    }

    private void syncToAllServer(ClientEvent event) {
        Client client = event.getClient();
        //Only ephemeral data sync by Distro, persist client should sync by raft.
        //临时实例使用Distro协议，持久化实例使用Raft协议
        //ClientManager.isResponsibleClient()方法，判断只有该client的责任节点才能进行集群数据同步
        if (null == client || !client.isEphemeral() || !clientManager.isResponsibleClient(client)) {
            return;
        }
        if (event instanceof ClientEvent.ClientDisconnectEvent) {
            //如果event是客户端注销实例时需要进行集群节点同步的事件
            DistroKey distroKey = new DistroKey(client.getClientId(), TYPE);
            distroProtocol.sync(distroKey, DataOperation.DELETE);
        } else if (event instanceof ClientEvent.ClientChangedEvent) {
            //如果event是客户端注册实例时需要进行集群节点同步的事件
            DistroKey distroKey = new DistroKey(client.getClientId(), TYPE);
            distroProtocol.sync(distroKey, DataOperation.CHANGE);
        }
    }
    ...
}

(4)总结

在Nacos 1.4.1版本中的服务健康检查：是15s没心跳则把健康状态修改为不健康，30s没心跳则把实例对象移除。

在Nacos 2.1.0版本中的服务健康检查：是20s没心跳则把客户端放入一个过期集合，此时并不移除客户端连接。由于引入了gRPC长连接，所以可以新增探活机制检查过期集合中的连接。服务端发送探活请求给客户端时的代价并不大，可确保客户端下线。

8.服务下线如何注销注册表和客户端等信息

(1)客户端发出服务下线请求的源码

(2)服务端处理服务下线请求的源码

(1)客户端发出服务下线请求的源码

Nacos客户端发起服务下线的入口在AbstractAutoServiceRegistration这个类之中，而AbstractAutoServiceRegistration是nacos-discovery中的类。

由于AbstractAutoServiceRegistration的destroy()方法被@PreDestroy修饰，所以当容器关闭时，会调用AbstractAutoServiceRegistration的destroy()方法。该方法最后会触发调用NacosNamingService的deregisterInstance()方法，然后调用NamingClientProxyDelegate的deregisterService()方法，接着调用NamingGrpcClientProxy的deregisterService()方法。和客户端发起服务注册一样，首先会创建请求参数对象，然后通过NamingGrpcClientProxy的requestToServer()方法发起请求，也就是调用RpcClient的request()方法发起gRPC请求进行服务下线。

public abstract class AbstractAutoServiceRegistration<R extends Registration>
    implements AutoServiceRegistration, ApplicationContextAware, ApplicationListener<WebServerInitializedEvent> {
    ...

    @PreDestroy
    public void destroy() {
        stop();
    }

    public void stop() {
        if (this.getRunning().compareAndSet(true, false) && isEnabled()) {
            deregister();
            if (shouldRegisterManagement()) {
                deregisterManagement();
            }
            this.serviceRegistry.close();
        }
    }

    protected void deregister() {
        this.serviceRegistry.deregister(getRegistration());
    }
    ...
}

public class NacosServiceRegistry implements ServiceRegistry<Registration> {
    ...
    @Override
    public void deregister(Registration registration) {
        log.info("De-registering from Nacos Server now...");
        if (StringUtils.isEmpty(registration.getServiceId())) {
            log.warn("No dom to de-register for nacos client...");
            return;
        }
        NamingService namingService = namingService();
        String serviceId = registration.getServiceId();
        String group = nacosDiscoveryProperties.getGroup();
        try {
            //调用NacosNamingService.deregisterInstance()方法
            namingService.deregisterInstance(serviceId, group, registration.getHost(), registration.getPort(), nacosDiscoveryProperties.getClusterName());
        } catch (Exception e) {
            log.error("ERR_NACOS_DEREGISTER, de-register failed...{},", registration.toString(), e);
        }
        log.info("De-registration finished.");
    }
    ...
}

@SuppressWarnings("PMD.ServiceOrDaoClassShouldEndWithImplRule")
public class NacosNamingService implements NamingService {
    private NamingClientProxy clientProxy;
    ...

    public NacosNamingService(Properties properties) throws NacosException {
        init(properties);
    }

    private void init(Properties properties) throws NacosException {
        ...
        this.clientProxy = new NamingClientProxyDelegate(this.namespace, serviceInfoHolder, properties, changeNotifier);
    }

    @Override
    public void deregisterInstance(String serviceName, String groupName, String ip, int port, String clusterName) throws NacosException {
        Instance instance = new Instance();
        instance.setIp(ip);
        instance.setPort(port);
        instance.setClusterName(clusterName);
        deregisterInstance(serviceName, groupName, instance);
    }

    @Override
    public void deregisterInstance(String serviceName, String groupName, Instance instance) throws NacosException {
        //调用NamingClientProxyDelegate.deregisterService()方法
        clientProxy.deregisterService(serviceName, groupName, instance);
    }
    ...
}

public class NamingClientProxyDelegate implements NamingClientProxy {
    private final NamingHttpClientProxy httpClientProxy;
    private final NamingGrpcClientProxy grpcClientProxy;
    ...

    public NamingClientProxyDelegate(String namespace, ServiceInfoHolder serviceInfoHolder, Properties properties, InstancesChangeNotifier changeNotifier) throws NacosException {
        ...
        this.httpClientProxy = new NamingHttpClientProxy(namespace, securityProxy, serverListManager, properties, serviceInfoHolder);
        this.grpcClientProxy = new NamingGrpcClientProxy(namespace, securityProxy, serverListManager, properties, serviceInfoHolder);
    }

    @Override
    public void deregisterService(String serviceName, String groupName, Instance instance) throws NacosException {
        getExecuteClientProxy(instance).deregisterService(serviceName, groupName, instance);
    }

    private NamingClientProxy getExecuteClientProxy(Instance instance) {
        return instance.isEphemeral() ? grpcClientProxy : httpClientProxy;
    }
    ...
}

public class NamingGrpcClientProxy extends AbstractNamingClientProxy {
    private final NamingGrpcRedoService redoService;
    ...

    @Override
    public void deregisterService(String serviceName, String groupName, Instance instance) throws NacosException {
        NAMING_LOGGER.info("[DEREGISTER-SERVICE] {} deregistering service {} with instance: {}", namespaceId, serviceName, instance);
        redoService.instanceDeregister(serviceName, groupName);
        doDeregisterService(serviceName, groupName, instance);
    }

    //Execute deregister operation.
    public void doDeregisterService(String serviceName, String groupName, Instance instance) throws NacosException {
        //创建请求参数对象
        InstanceRequest request = new InstanceRequest(namespaceId, serviceName, groupName, NamingRemoteConstants.DE_REGISTER_INSTANCE, instance);
        //向服务端发起请求
        requestToServer(request, Response.class);
        redoService.removeInstanceForRedo(serviceName, groupName);
    }

    private <T extends Response> T requestToServer(AbstractNamingRequest request, Class<T> responseClass) throws NacosException {
        try {
            request.putAllHeader(getSecurityHeaders(request.getNamespace(), request.getGroupName(), request.getServiceName()));
            //实际会调用RpcClient.request()方法发起gRPC请求
            Response response = requestTimeout < 0 ? rpcClient.request(request) : rpcClient.request(request, requestTimeout);
            if (ResponseCode.SUCCESS.getCode() != response.getResultCode()) {
                throw new NacosException(response.getErrorCode(), response.getMessage());
            }
            if (responseClass.isAssignableFrom(response.getClass())) {
                return (T) response;
            }
            NAMING_LOGGER.error("Server return unexpected response '{}', expected response should be '{}'", response.getClass().getName(), responseClass.getName());
        } catch (Exception e) {
            throw new NacosException(NacosException.SERVER_ERROR, "Request nacos server failed: ", e);
        }
        throw new NacosException(NacosException.SERVER_ERROR, "Server return invalid response");
    }
    ...
}

(2)服务端处理服务下线请求的源码

服务注册时请求参数InstanceRequest的类型是REGISTER_INSTANCE，服务下线时请求参数InstanceRequest的类型是DE_REGISTER_INSTANCE。

处理服务注册和服务下线的入口是InstanceRequestHandler的handle()方法，这个方法会触发调用InstanceRequestHandler的deregisterInstance()方法，也就是调用EphemeralClientOperationServiceImpl的deregisterInstance()方法。

在EphemeralClientOperationServiceImpl的deregisterInstance()方法中，会在移除Client对象中的instance信息时，发布ClientChangedEvent事件，然后接着发布客户端注销服务实例的事件ClientDeregisterServiceEvent。

其中ClientChangedEvent事件是用来同步数据给集群节点的，ClientDeregisterServiceEvent事件是用来移除注册表 + 订阅表的服务实例。移除注册表 + 订阅表的服务实例时，还会发布ServiceChangeEvent事件，ServiceChangeEvent事件是用来通知订阅了该服务的Nacos客户端的。同理，服务注册时其实也会发布类似的三个事件。

@Component
public class InstanceRequestHandler extends RequestHandler<InstanceRequest, InstanceResponse> {
    private final EphemeralClientOperationServiceImpl clientOperationService;

    public InstanceRequestHandler(EphemeralClientOperationServiceImpl clientOperationService) {
        this.clientOperationService = clientOperationService;
    }

    @Override
    @Secured(action = ActionTypes.WRITE)
    public InstanceResponse handle(InstanceRequest request, RequestMeta meta) throws NacosException {
        //根据请求信息创建一个Service对象，里面包含了：命名空间、分组名、服务名
        Service service = Service.newService(request.getNamespace(), request.getGroupName(), request.getServiceName(), true);
        switch (request.getType()) {
            case NamingRemoteConstants.REGISTER_INSTANCE:
                //注册实例
                return registerInstance(service, request, meta);
            case NamingRemoteConstants.DE_REGISTER_INSTANCE:
                //注销实例
                return deregisterInstance(service, request, meta);
            default:
                throw new NacosException(NacosException.INVALID_PARAM, String.format("Unsupported request type %s", request.getType()));
        }
    }

    private InstanceResponse registerInstance(Service service, InstanceRequest request, RequestMeta meta) {
        //调用EphemeralClientOperationServiceImpl的注册方法registerInstance()，这里需要注意如下参数；
        //参数service：根据请求信息创建的一个Service对象，里面有命名空间、分组名、服务名
        //参数request.getInstance()：这个参数就对应了客户端的实例对象，里面包含IP、端口等信息
        //参数meta.getConnectionId()：这个参数很关键，它是连接ID
        clientOperationService.registerInstance(service, request.getInstance(), meta.getConnectionId());
        return new InstanceResponse(NamingRemoteConstants.REGISTER_INSTANCE);
    }

    private InstanceResponse deregisterInstance(Service service, InstanceRequest request, RequestMeta meta) {
        //调用EphemeralClientOperationServiceImpl的注销方法deregisterInstance()
        clientOperationService.deregisterInstance(service, request.getInstance(), meta.getConnectionId());
        return new InstanceResponse(NamingRemoteConstants.DE_REGISTER_INSTANCE);
    }
}

@Component("ephemeralClientOperationService")
public class EphemeralClientOperationServiceImpl implements ClientOperationService {
    private final ClientManager clientManager;
    ...

    @Override
    public void deregisterInstance(Service service, Instance instance, String clientId) {
        if (!ServiceManager.getInstance().containSingleton(service)) {
            Loggers.SRV_LOG.warn("remove instance from non-exist service: {}", service);
            return;
        }
        //从ServiceManager中根据由请求信息创建的Service对象获取一个已注册的Service对象
        Service singleton = ServiceManager.getInstance().getSingleton(service);
        //从ClientManagerDelegate中根据请求参数中的connectionId获取一个Client对象，即IpPortBasedClient对象
        Client client = clientManager.getClient(clientId);
        if (!clientIsLegal(client, clientId)) {
            return;
        }
        //调用AbstractClient.removeServiceInstance()方法
        //移除Client对象中的instance信息并发布ClientChangedEvent事件来同步集群节点
        InstancePublishInfo removedInstance = client.removeServiceInstance(singleton);
        client.setLastUpdatedTime();
        if (null != removedInstance) {
            //发布客户端注销服务实例的事件
            NotifyCenter.publishEvent(new ClientOperationEvent.ClientDeregisterServiceEvent(singleton, clientId));
            NotifyCenter.publishEvent(new MetadataEvent.InstanceMetadataEvent(singleton, removedInstance.getMetadataId(), true));
        }
    }
    ...
}

public abstract class AbstractClient implements Client {
    //publishers其实就是记录该客户端提供的服务和服务实例，一个客户端可提供多个服务
    //存储客户端发送过来的请求中的Instance信息，当然这些信息已封装为InstancePublishInfo对象
    //key为已注册的Service，value是根据请求中的instance实例信息封装的InstancePublishInfo对象
    protected final ConcurrentHashMap<Service, InstancePublishInfo> publishers = new ConcurrentHashMap<>(16, 0.75f, 1);
    ...

    @Override
    public InstancePublishInfo removeServiceInstance(Service service) {
        InstancePublishInfo result = publishers.remove(service);
        if (null != result) {
            MetricsMonitor.decrementInstanceCount();
            //发布客户端改变事件，用于处理集群间的数据同步
            NotifyCenter.publishEvent(new ClientEvent.ClientChangedEvent(this));
        }
        Loggers.SRV_LOG.info("Client remove for service {}, {}", service, getClientId());
        return result;
    }
    ...
}

一.处理ClientChangedEvent事件

也就是同步数据到集群节点：

public class DistroClientDataProcessor extends SmartSubscriber implements DistroDataStorage, DistroDataProcessor {
    ...
    @Override
    public void onEvent(Event event) {
        ...
        if (event instanceof ClientEvent.ClientVerifyFailedEvent) {
            syncToVerifyFailedServer((ClientEvent.ClientVerifyFailedEvent) event);
        } else {
            syncToAllServer((ClientEvent) event);
        }
    }

    private void syncToAllServer(ClientEvent event) {
        Client client = event.getClient();
        //Only ephemeral data sync by Distro, persist client should sync by raft.
        //临时实例使用Distro协议，持久化实例使用Raft协议
        //ClientManager.isResponsibleClient()方法，判断只有该client的责任节点才能进行集群数据同步
        if (null == client || !client.isEphemeral() || !clientManager.isResponsibleClient(client)) {
            return;
        }
        if (event instanceof ClientEvent.ClientDisconnectEvent) {
            //如果event是客户端注销实例时需要进行集群节点同步的事件
            DistroKey distroKey = new DistroKey(client.getClientId(), TYPE);
            distroProtocol.sync(distroKey, DataOperation.DELETE);
        } else if (event instanceof ClientEvent.ClientChangedEvent) {
            //如果event是客户端注册实例时需要进行集群节点同步的事件
            DistroKey distroKey = new DistroKey(client.getClientId(), TYPE);
            distroProtocol.sync(distroKey, DataOperation.CHANGE);
        }
    }
    ...
}

@Component
public class DistroProtocol {
    private final ServerMemberManager memberManager;
    private final DistroTaskEngineHolder distroTaskEngineHolder;
    ...

    //Start to sync by configured delay.
    public void sync(DistroKey distroKey, DataOperation action) {
        sync(distroKey, action, DistroConfig.getInstance().getSyncDelayMillis());
    }

    //Start to sync data to all remote server.
    public void sync(DistroKey distroKey, DataOperation action, long delay) {
        //遍历集群中除自身节点外的其他节点
        for (Member each : memberManager.allMembersWithoutSelf()) {
            syncToTarget(distroKey, action, each.getAddress(), delay);
        }
    }

    //Start to sync to target server.
    public void syncToTarget(DistroKey distroKey, DataOperation action, String targetServer, long delay) {
        //先把要同步的集群节点targetServer包装成DistroKey对象
        DistroKey distroKeyWithTarget = new DistroKey(distroKey.getResourceKey(), distroKey.getResourceType(), targetServer);
        //然后根据DistroKey对象创建DistroDelayTask任务
        DistroDelayTask distroDelayTask = new DistroDelayTask(distroKeyWithTarget, action, delay);
        //接着调用NacosDelayTaskExecuteEngine.addTask()方法
        //往延迟任务执行引擎DistroDelayTaskExecuteEngine中添加延迟任务DistroDelayTask
        distroTaskEngineHolder.getDelayTaskExecuteEngine().addTask(distroKeyWithTarget, distroDelayTask);
        if (Loggers.DISTRO.isDebugEnabled()) {
            Loggers.DISTRO.debug("[DISTRO-SCHEDULE] {} to {}", distroKey, targetServer);
        }
    }
    ...
}

二.处理ClientDeregisterServiceEvent事件

也就是移除注册表 + 订阅表的服务实例：

@Component
public class ClientServiceIndexesManager extends SmartSubscriber {
    //注册表(服务提供者)，一个Service服务对象，对应多个服务实例的clientId
    private final ConcurrentMap<Service, Set<String>> publisherIndexes = new ConcurrentHashMap<>();

    //订阅者列表(服务消费者)，一个Service服务对象，对应多个订阅者的clientId
    private final ConcurrentMap<Service, Set<String>> subscriberIndexes = new ConcurrentHashMap<>();

    ...
    @Override
    public void onEvent(Event event) {
        if (event instanceof ClientEvent.ClientDisconnectEvent) {
            handleClientDisconnect((ClientEvent.ClientDisconnectEvent) event);
        } else if (event instanceof ClientOperationEvent) {
            handleClientOperation((ClientOperationEvent) event);
        }
    }

    private void handleClientOperation(ClientOperationEvent event) {
        Service service = event.getService();
        String clientId = event.getClientId();
        if (event instanceof ClientOperationEvent.ClientRegisterServiceEvent) {
            //处理客户端注册事件ClientRegisterServiceEvent
            addPublisherIndexes(service, clientId);
        } else if (event instanceof ClientOperationEvent.ClientDeregisterServiceEvent) {
            //处理客户端注销事件ClientDeregisterServiceEvent
            removePublisherIndexes(service, clientId);
        } else if (event instanceof ClientOperationEvent.ClientSubscribeServiceEvent) {
            //处理客户端订阅服务事件ClientSubscribeServiceEvent
            addSubscriberIndexes(service, clientId);
        } else if (event instanceof ClientOperationEvent.ClientUnsubscribeServiceEvent) {
            //处理客户端取消订阅事件ClientUnsubscribeServiceEvent
            removeSubscriberIndexes(service, clientId);
        }
    }

    private void removePublisherIndexes(Service service, String clientId) {
        if (!publisherIndexes.containsKey(service)) {
            return;
        }
        //移除注册表中的服务实例
        publisherIndexes.get(service).remove(clientId);
        //发布服务改变事件ServiceChangedEvent
        NotifyCenter.publishEvent(new ServiceEvent.ServiceChangedEvent(service, true));
    }
    ...
}

三.处理ServiceChangeEvent事件

也就是通知订阅了该服务的客户端：

@org.springframework.stereotype.Service
public class NamingSubscriberServiceV2Impl extends SmartSubscriber implements NamingSubscriberService {
    ...
    @Override
    public void onEvent(Event event) {
        if (!upgradeJudgement.isUseGrpcFeatures()) {
            return;
        }
        if (event instanceof ServiceEvent.ServiceChangedEvent) {
            //If service changed, push to all subscribers.
            //如果服务变动，会向Service服务的所有订阅者推送Service服务的实例信息，让订阅者(客户端)更新本地缓存
            ServiceEvent.ServiceChangedEvent serviceChangedEvent = (ServiceEvent.ServiceChangedEvent) event;
            Service service = serviceChangedEvent.getService();
            //调用NacosDelayTaskExecuteEngine.addTask()方法，往延迟任务执行引擎添加任务
            delayTaskEngine.addTask(service, new PushDelayTask(service, PushConfig.getInstance().getPushTaskDelay()));
        } else if (event instanceof ServiceEvent.ServiceSubscribedEvent) {
            //If service is subscribed by one client, only push this client.
            //如果Service服务被一个客户端订阅，则只推送Service服务的实例信息给该客户端
            ServiceEvent.ServiceSubscribedEvent subscribedEvent = (ServiceEvent.ServiceSubscribedEvent) event;
            Service service = subscribedEvent.getService();
            //调用NacosDelayTaskExecuteEngine.addTask()方法，往延迟任务执行引擎添加任务
            delayTaskEngine.addTask(service, new PushDelayTask(service, PushConfig.getInstance().getPushTaskDelay(), subscribedEvent.getClientId()));
        }
    }
    ...
}

(3)总结

9.事件驱动架构源码分析

(1)如何使用Nacos的事件发布

(2)Nacos通知中心的事件发布源码

(3)Nacos通知中心注册订阅者的源码

Nacos 2.x大量使用了事件发布的动作，比如客户端注册服务实例、客户端下线服务实例、服务改变、服务订阅等。

(1)如何使用Nacos的事件发布

一.首先自定义一个事件

下面定义了一个名为TestEvent的事件，继承自Nacos的Event类。

import com.alibaba.nacos.common.notify.Event;

public class TestEvent extends Event {

}

二.然后定义一个订阅者

有了事件之后，还需要一个订阅者，这样发布的事件才能被这个订阅者进行处理。

自定义的订阅者需要继承Nacos的SmartSubscriber抽象类，自定义的订阅者需要实现三个方法。

方法一：构造方法

需要将自定义的订阅者注册到Nacos的通知中心NotifyCenter里，这样NotifyCenter在发布自定义事件时，才能让自定义的订阅者进行响应。

方法二：subscribeTypes()方法

实现该方法时，需要把自定义的事件添加到方法的返回结果中，所以可以通过该方法获取自定义订阅者监听了哪些事件。

方法三：onEvent()方法

Nacos的通知中心NotifyCenter在发布自定义事件时，便会调用该方法，所以该方法中需要实现自定义订阅者对自定义事件的处理。

import com.alibaba.nacos.common.notify.Event;
import com.alibaba.nacos.common.notify.NotifyCenter;
import com.alibaba.nacos.common.notify.listener.SmartSubscriber;
import org.springframework.stereotype.Component;
import java.util.LinkedList;
import java.util.List;

//自定义的订阅者需要继承Nacos的SmartSubscriber抽象类
@Component
public class TestSubscriber extends SmartSubscriber {
    //构造方法中需要将自定义的订阅者TestSubscriber注册到Nacos的通知中心NotifyCenter
    public TestSubscriber() {
        NotifyCenter.registerSubscriber(this);
    }

    //实现subscribeTypes()方法时，把自定义的事件TestEvent添加进去返回
    @Override
    public List<Class<? extends Event>> subscribeTypes() {
        List<Class<? extends Event>> result = new LinkedList<>();
        result.add(TestEvent.class);
        return result;
    }

    //实现onEvent()方法
    //当Nacos的通知中心NotifyCenter发布一个TestEvent事件时，就会响应该方法处理订阅者的逻辑
    @Override
    public void onEvent(Event event) {
        System.out.println("TestSubscriber onEvent");
    }
}

三.最后通过Nacos的通知中心NotifyCenter发布自定义事件

这样便完成了自定义事件、自定义订阅者通过Nacos实现发布订阅功能。

@RestController
@RequestMapping("/sub/")
public class SubscriberController {
    @GetMapping("/test")
    public void test() {
        NotifyCenter.publishEvent(new TestEvent());
    }
}

(2)Nacos通知中心的事件发布源码

通知中心NotifyCenter执行publishEvent()方法发布事件时，比如会调用DefaultPublisher的publish()方法来发布事件。

DefaultPublisher的publish()方法会先把事件放入到一个阻塞队列queue中，而在DefaultPublisher创建时会启动一个线程从阻塞队列取出事件来处理。处理时就会调用到DefaultPublisher的receiveEvent()方法通知事件订阅者，也就是执行DefaultPublisher的notifySubscriber()方法通知事件订阅者。

在DefaultPublisher的notifySubscriber()方法中，首先会创建一个调用订阅者的onEvent()方法的任务，然后如果订阅者有线程池，则将任务提交给订阅者的线程池去执行。如果订阅者没有线程池，则直接执行该任务。

可见事件的发布也使用了阻塞队列 + 异步任务，来实现对订阅者的通知。

public class NotifyCenter {
    private static final NotifyCenter INSTANCE = new NotifyCenter();
    //key是事件Class的canonicalName，value是EventPublisher对象，一个事件对应一个EventPublisher对象
    //在EventPublisher对象中就会包含订阅了该事件的所有订阅者
    //EventPublisher的实现类有DefaultPublisher、NamingEventPublisher
    private final Map<String, EventPublisher> publisherMap = new ConcurrentHashMap<>(16);
    ...

    //Request publisher publish event Publishers load lazily, calling publisher. Start () only when the event is actually published.
    public static boolean publishEvent(final Event event) {
        try {
            return publishEvent(event.getClass(), event);
        } catch (Throwable ex) {
            LOGGER.error("There was an exception to the message publishing : ", ex);
            return false;
        }
    }

    //Request publisher publish event Publishers load lazily, calling publisher.
    private static boolean publishEvent(final Class<? extends Event> eventType, final Event event) {
        if (ClassUtils.isAssignableFrom(SlowEvent.class, eventType)) {
            return INSTANCE.sharePublisher.publish(event);
        }
        //获取发布的事件的Class的canonicalName
        final String topic = ClassUtils.getCanonicalName(eventType);
        //根据发布事件类型获取EventPublisher对象，该对象中会包含所发布事件的所有订阅者信息
        EventPublisher publisher = INSTANCE.publisherMap.get(topic);
        if (publisher != null) {
            //比如调用DefaultPublisher.publish()方法发布事件
            return publisher.publish(event);
        }
        LOGGER.warn("There are no [{}] publishers for this event, please register", topic);
        return false;
    }
    ...
}

//The default event publisher implementation.
//一个事件只会对应一个DefaultPublisher
public class DefaultPublisher extends Thread implements EventPublisher {
    private Class<? extends Event> eventType;

    //阻塞队列存放待发布的事件
    private BlockingQueue<Event> queue;

    //Class为eventType的事件的所有订阅者
    protected final ConcurrentHashSet<Subscriber> subscribers = new ConcurrentHashSet<>();

    @Override
    public void init(Class<? extends Event> type, int bufferSize) {
        ...
        start();
    }

    @Override
    public synchronized void start() {
        if (!initialized) {
            super.start();
            ...
        }
    }

    @Override
    public void run() {
        openEventHandler();
    }

    void openEventHandler() {
        try {
            ...
            for (; ;) {
                ...
                //从阻塞队列取数据
                final Event event = queue.take();
                //处理事件
                receiveEvent(event);
                ...
            }
        } catch (Throwable ex) {
            LOGGER.error("Event listener exception : ", ex);
        }
    }
    ...

    @Override
    public boolean publish(Event event) {
        checkIsStart();
        //把事件放入到了一个阻塞队列queue中，由DefaultPublisher创建时启动的线程来处理
        boolean success = this.queue.offer(event);
        if (!success) {//如果事件放入阻塞队列失败，则直接处理
            LOGGER.warn("Unable to plug in due to interruption, synchronize sending time, event : {}", event);
            //通知事件的订阅者去进行事件处理
            receiveEvent(event);
            return true;
        }
        return true;
    }

    //通知事件的订阅者去进行事件处理
    void receiveEvent(Event event) {
        ...
        //遍历当前事件的订阅者，对订阅者执行notifySubscriber()方法，实际上就是执行订阅者的onEvent()方法
        for (Subscriber subscriber : subscribers) {
            ...
            //触发执行订阅者的onEvent()方法，实现对订阅者的通知
            notifySubscriber(subscriber, event);
        }
    }

    @Override
    public void notifySubscriber(final Subscriber subscriber, final Event event) {
        //创建一个任务，该任务会调用订阅者的onEvent方法
        final Runnable job = () -> subscriber.onEvent(event);
        final Executor executor = subscriber.executor();
        if (executor != null) {
            //将任务提交给订阅者的线程池去执行
            executor.execute(job);
        } else {
            try {
                //如果订阅者没有线程池，则直接执行该任务
                job.run();
            } catch (Throwable e) {
                LOGGER.error("Event callback exception: ", e);
            }
        }
    }
    ...
}

(3)Nacos通知中心注册订阅者的源码

在执行NotifyCenter的registerSubscriber()方法注册订阅者时，会调用订阅者实现的subscribeTypes()方法获取订阅者要监听的所有事件，然后遍历这些事件并调用NotifyCenter的addSubscriber()方法。

执行NotifyCenter的addSubscriber()方法时会为这些事件添加订阅者。由于每个事件都会对应一个EventPublisher对象，所以会先从NotifyCenter.publisherMap中获取EventPublisher对象，然后调用EventPublisher的addSubscriber()方法向EventPublisher添加订阅者，从而完成向通知中心注册订阅者。

public class NotifyCenter {
    private static final NotifyCenter INSTANCE = new NotifyCenter();

    //key是事件Class的canonicalName，value是EventPublisher对象，一个事件对应一个EventPublisher对象
    //在EventPublisher对象中就会包含订阅了该事件的所有订阅者
    //EventPublisher的实现类有DefaultPublisher、NamingEventPublisher
    private final Map<String, EventPublisher> publisherMap = new ConcurrentHashMap<>(16);
    ...

    public static void registerSubscriber(final Subscriber consumer) {
        //注册订阅者
        registerSubscriber(consumer, DEFAULT_PUBLISHER_FACTORY);
    }

    public static void registerSubscriber(final Subscriber consumer, final EventPublisherFactory factory) {
        if (consumer instanceof SmartSubscriber) {
            //调用subscribeTypes()方法获取订阅者consumer需要监听的事件，然后对这些事件进行遍历
            for (Class<? extends Event> subscribeType : ((SmartSubscriber) consumer).subscribeTypes()) {
                //For case, producer: defaultSharePublisher -> consumer: smartSubscriber.
                if (ClassUtils.isAssignableFrom(SlowEvent.class, subscribeType)) {
                    //添加订阅者
                    INSTANCE.sharePublisher.addSubscriber(consumer, subscribeType);
                } else {
                    //For case, producer: defaultPublisher -> consumer: subscriber.
                    //添加订阅者
                    addSubscriber(consumer, subscribeType, factory);
                }
            }
            return;
        }

        final Class<? extends Event> subscribeType = consumer.subscribeType();
        if (ClassUtils.isAssignableFrom(SlowEvent.class, subscribeType)) {
            INSTANCE.sharePublisher.addSubscriber(consumer, subscribeType);
            return;
        }
        addSubscriber(consumer, subscribeType, factory);
    }

    //Add a subscriber to publisher.
    private static void addSubscriber(final Subscriber consumer, Class<? extends Event> subscribeType, EventPublisherFactory factory) {
        //获取订阅的事件的Class的canonicalName
        final String topic = ClassUtils.getCanonicalName(subscribeType);
        synchronized (NotifyCenter.class) {
            //MapUtils.computeIfAbsent is a unsafe method.
            //创建EventPublisher对象，一个事件会对应一个EventPublisher对象
            MapUtil.computeIfAbsent(INSTANCE.publisherMap, topic, factory, subscribeType, ringBufferSize);
        }

        //获取事件对应的EventPublisher对象，比如DefaultPublisher对象
        EventPublisher publisher = INSTANCE.publisherMap.get(topic);
        if (publisher instanceof ShardedEventPublisher) {
            ((ShardedEventPublisher) publisher).addSubscriber(consumer, subscribeType);
        } else {
            //往EventPublisher对象添加订阅者信息，比如调用DefaultPublisher.addSubscriber()方法
            publisher.addSubscriber(consumer);
        }
    }
    ...
}

//一个事件只会对应一个DefaultPublisher
public class DefaultPublisher extends Thread implements EventPublisher {
    private Class<? extends Event> eventType;
    //Class为eventType的事件的所有订阅者
    protected final ConcurrentHashSet<Subscriber> subscribers = new ConcurrentHashSet<>();
    ...

    @Override
    public void addSubscriber(Subscriber subscriber) {
        //添加订阅者
        subscribers.add(subscriber);
    }
    ...
}