聊聊NacosNamingService的subscribe及unsubscribe

序

本文主要研究一下 NacosNamingService 的 subscribe 及 unsubscribe

NacosNamingService

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java

public class NacosNamingService implements NamingService {
    private static final String DEFAULT_PORT = "8080";
    private static final long DEFAULT_HEART_BEAT_INTERVAL = TimeUnit.SECONDS.toMillis(5);

    /**
     * Each Naming instance should have different namespace.
     */
    private String namespace;

    private String endpoint;

    private String serverList;

    private String cacheDir;

    private String logName;

    private HostReactor hostReactor;

    private BeatReactor beatReactor;

    private EventDispatcher eventDispatcher;

    private NamingProxy serverProxy;

    //......

    @Override
    public void subscribe(String serviceName, EventListener listener) throws NacosException {subscribe(serviceName, new ArrayList<String>(), listener);
    }

    @Override
    public void subscribe(String serviceName, String groupName, EventListener listener) throws NacosException {subscribe(serviceName, groupName, new ArrayList<String>(), listener);
    }

    @Override
    public void subscribe(String serviceName, List<String> clusters, EventListener listener) throws NacosException {subscribe(serviceName, Constants.DEFAULT_GROUP, clusters, listener);
    }

    @Override
    public void subscribe(String serviceName, String groupName, List<String> clusters, EventListener listener) throws NacosException {eventDispatcher.addListener(hostReactor.getServiceInfo(NamingUtils.getGroupedName(serviceName, groupName),
            StringUtils.join(clusters, ",")), StringUtils.join(clusters, ","), listener);
    }

    @Override
    public void unsubscribe(String serviceName, EventListener listener) throws NacosException {unsubscribe(serviceName, new ArrayList<String>(), listener);
    }

    @Override
    public void unsubscribe(String serviceName, String groupName, EventListener listener) throws NacosException {unsubscribe(serviceName, groupName, new ArrayList<String>(), listener);
    }

    @Override
    public void unsubscribe(String serviceName, List<String> clusters, EventListener listener) throws NacosException {unsubscribe(serviceName, Constants.DEFAULT_GROUP, clusters, listener);
    }

    @Override
    public void unsubscribe(String serviceName, String groupName, List<String> clusters, EventListener listener) throws NacosException {eventDispatcher.removeListener(NamingUtils.getGroupedName(serviceName, groupName), StringUtils.join(clusters, ","), listener);
    }

    //......
}

• subscribe 方法执行 eventDispatcher.addListener；unsubscribe 方法执行 eventDispatcher.removeListener

EventDispatcher

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/core/EventDispatcher.java

public class EventDispatcher {

    private ExecutorService executor = null;

    private BlockingQueue<ServiceInfo> changedServices = new LinkedBlockingQueue<ServiceInfo>();

    private ConcurrentMap<String, List<EventListener>> observerMap
        = new ConcurrentHashMap<String, List<EventListener>>();

    public EventDispatcher() {executor = Executors.newSingleThreadExecutor(new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {Thread thread = new Thread(r, "com.alibaba.nacos.naming.client.listener");
                thread.setDaemon(true);

                return thread;
            }
        });

        executor.execute(new Notifier());
    }

    public void addListener(ServiceInfo serviceInfo, String clusters, EventListener listener) {NAMING_LOGGER.info("[LISTENER] adding" + serviceInfo.getName() + "with" + clusters + "to listener map");
        List<EventListener> observers = Collections.synchronizedList(new ArrayList<EventListener>());
        observers.add(listener);

        observers = observerMap.putIfAbsent(ServiceInfo.getKey(serviceInfo.getName(), clusters), observers);
        if (observers != null) {observers.add(listener);
        }

        serviceChanged(serviceInfo);
    }

    public void removeListener(String serviceName, String clusters, EventListener listener) {NAMING_LOGGER.info("[LISTENER] removing" + serviceName + "with" + clusters + "from listener map");

        List<EventListener> observers = observerMap.get(ServiceInfo.getKey(serviceName, clusters));
        if (observers != null) {Iterator<EventListener> iter = observers.iterator();
            while (iter.hasNext()) {EventListener oldListener = iter.next();
                if (oldListener.equals(listener)) {iter.remove();
                }
            }
            if (observers.isEmpty()) {observerMap.remove(ServiceInfo.getKey(serviceName, clusters));
            }
        }
    }

    public List<ServiceInfo> getSubscribeServices() {List<ServiceInfo> serviceInfos = new ArrayList<ServiceInfo>();
        for (String key : observerMap.keySet()) {serviceInfos.add(ServiceInfo.fromKey(key));
        }
        return serviceInfos;
    }

    public void serviceChanged(ServiceInfo serviceInfo) {if (serviceInfo == null) {return;}

        changedServices.add(serviceInfo);
    }

    private class Notifier implements Runnable {
        @Override
        public void run() {while (true) {
                ServiceInfo serviceInfo = null;
                try {serviceInfo = changedServices.poll(5, TimeUnit.MINUTES);
                } catch (Exception ignore) { }

                if (serviceInfo == null) {continue;}

                try {List<EventListener> listeners = observerMap.get(serviceInfo.getKey());

                    if (!CollectionUtils.isEmpty(listeners)) {for (EventListener listener : listeners) {List<Instance> hosts = Collections.unmodifiableList(serviceInfo.getHosts());
                            listener.onEvent(new NamingEvent(serviceInfo.getName(), serviceInfo.getGroupName(), serviceInfo.getClusters(), hosts));
                        }
                    }

                } catch (Exception e) {NAMING_LOGGER.error("[NA] notify error for service:"
                        + serviceInfo.getName() + ", clusters:" + serviceInfo.getClusters(), e);
                }
            }
        }
    }

    public void setExecutor(ExecutorService executor) {
        ExecutorService oldExecutor = this.executor;
        this.executor = executor;

        oldExecutor.shutdown();}
}

• EventDispatcher 的构造器创建了 executor，并执行 Notifier；Notifier 使用一个 while true 循环不断执行 changedServices.poll(5, TimeUnit.MINUTES) 拉取 serviceInfo，拉取到的话会从 observerMap 取出对应的 EventListener 列表，然后挨个回调 listener.onEvent 方法
• addListener 方法则是往 observerMap 创建或添加 observers，然后执行 serviceChanged 方法；removeListener 则是从 observerMap 移除指定的 listener，如果指定 key 的 listener 列表为空则删除该 key
• serviceChanged 方法会往 changedServices 添加 serviceInfo；之后 Notifier 异步线程可用拉取信息执行 listener.onEvent 回调

小结

NacosNamingService 的 subscribe 方法执行 eventDispatcher.addListener；unsubscribe 方法执行 eventDispatcher.removeListener

doc

• NacosNamingService