Nacos源码—8.Nacos升级gRPC分析六

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

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);
    }
    ...
}