Nacos深入浅出（三）

 EventDispatcher.fireEvent(new ConfigDataChangeEvent(true, dataId, group, tenant, time.getTime()));

跟着代码一步步往下看：

public class EventDispatcher {

    /**
     * add event listener
     */
    static public void addEventListener(AbstractEventListener listener) {
        for (Class<? extends Event> type : listener.interest()) {
            getEntry(type).listeners.addIfAbsent(listener);
        }
    }

    /**
     * fire event, notify listeners.
     */
    static public void fireEvent(Event event) {
        if (null == event) {
            throw new IllegalArgumentException();
        }

        for (AbstractEventListener listener : getEntry(event.getClass()).listeners) {
            try {
                listener.onEvent(event);
            } catch (Exception e) {
                log.error(e.toString(), e);
            }
        }
    }

这个getEntry(event.getClass()).listeners需要重点看下

/**
     * get event listener for eventType. Add Entry if not exist.
     */
    static Entry getEntry(Class<? extends Event> eventType) {
        for (; ; ) {
            for (Entry entry : LISTENER_HUB) {
                if (entry.eventType == eventType) {
                    return entry;
                }
            }

            Entry tmp = new Entry(eventType);
            /**
             *  false means already exists
             */
            if (LISTENER_HUB.addIfAbsent(tmp)) {
                return tmp;
            }
        }
    }

    static final CopyOnWriteArrayList<Entry> LISTENER_HUB = new CopyOnWriteArrayList<Entry>();

这个LISTENER_HUB 会预先把几个相应的Entry 加载进去（这个我们后面分析），然后就开始onEvent，通知Listeners了；

@Service
public class AsyncNotifyService extends AbstractEventListener {

    @Override
    public List<Class<? extends Event>> interest() {
        List<Class<? extends Event>> types = new ArrayList<Class<? extends Event>>();
        // 触发配置变更同步通知
        types.add(ConfigDataChangeEvent.class);
        return types;
    }

    @Override
    public void onEvent(Event event) {

        // 并发产生 ConfigDataChangeEvent
        if (event instanceof ConfigDataChangeEvent) {
            ConfigDataChangeEvent evt = (ConfigDataChangeEvent)event;
            long dumpTs = evt.lastModifiedTs;
            String dataId = evt.dataId;
            String group = evt.group;
            String tenant = evt.tenant;
            String tag = evt.tag;
　　         // listen的服务地址
            List<?> ipList = serverListService.getServerList();

            // 其实这里任何类型队列都可以
            Queue<NotifySingleTask> queue = new LinkedList<NotifySingleTask>();
            for (int i = 0; i < ipList.size(); i++) {
                queue.add(new NotifySingleTask(dataId, group, tenant, tag, dumpTs, (String)ipList.get(i), evt.isBeta));
            }
            EXCUTOR.execute(new AsyncTask(httpclient, queue));
        }
    }

把这个配置关联的服务一个个通知下，建议大家可以结合观察者模式来理解这个；

    private static final Executor EXCUTOR = Executors.newScheduledThreadPool(100, new NotifyThreadFactory());

然后把这个通知服务扔到县线程池，放到另外一个线程中去执行通知任务；

 class AsyncTask implements Runnable {

        public AsyncTask(CloseableHttpAsyncClient httpclient, Queue<NotifySingleTask> queue) {
            this.httpclient = httpclient;
            this.queue = queue;
        }

        @Override
        public void run() {

            executeAsyncInvoke();

        }

        private void executeAsyncInvoke() {
            while (!queue.isEmpty()) {

                NotifySingleTask task = queue.poll();
                String targetIp = task.getTargetIP();
                if (serverListService.getServerList().contains(
                    targetIp)) {
                    // 启动健康检查且有不监控的ip则直接把放到通知队列，否则通知
                    if (serverListService.isHealthCheck()
                        && ServerListService.getServerListUnhealth().contains(targetIp)) {
                        // target ip 不健康，则放入通知列表中
                        ConfigTraceService.logNotifyEvent(task.getDataId(), task.getGroup(), task.getTenant(), null,
                            task.getLastModified(),
                            LOCAL_IP, ConfigTraceService.NOTIFY_EVENT_UNHEALTH, 0, task.target);
                        // get delay time and set fail count to the task
                        int delay = getDelayTime(task);
                        Queue<NotifySingleTask> queue = new LinkedList<NotifySingleTask>();
                        queue.add(task);
                        AsyncTask asyncTask = new AsyncTask(httpclient, queue);
                        ((ScheduledThreadPoolExecutor)EXCUTOR).schedule(asyncTask, delay, TimeUnit.MILLISECONDS);
                    } else {
                        HttpGet request = new HttpGet(task.url);
                        request.setHeader(NotifyService.NOTIFY_HEADER_LAST_MODIFIED,
                            String.valueOf(task.getLastModified()));
                        request.setHeader(NotifyService.NOTIFY_HEADER_OP_HANDLE_IP, LOCAL_IP);
                        if (task.isBeta) {
                            request.setHeader("isBeta", "true");
                        }
                        httpclient.execute(request, new AyscNotifyCallBack(httpclient, task));
                    }
                }
            }
        }

        private Queue<NotifySingleTask> queue;
        private CloseableHttpAsyncClient httpclient;

    }

上面这段代码明天再慢慢解析吧，加油！