RemoteConfigLongPollService：远程配置长轮循服务，负责长轮循ConfigServer变更通知，当有更新时立即轮循触发更新

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目录

概 述

RemoteConfigLongPollService：
远程配置长轮循服务，负责长轮循ConfigServer变更通知，当有更新时立即轮循触发更新
第一步RemetoConfigRepository构造中scheduleLongPollingRefresh()方法进入该类

private void scheduleLongPollingRefresh() {
    remoteConfigLongPollService.submit(m_namespace, this);
  }

进入RemoteCOnfigLongPollService下面方法

public boolean submit(String namespace, RemoteConfigRepository remoteConfigRepository) {
    boolean added = m_longPollNamespaces.put(namespace, remoteConfigRepository);
    m_notifications.putIfAbsent(namespace, INIT_NOTIFICATION_ID);
     若未启动长轮询定时任务，进行启动
    if (!m_longPollStarted.get()) {
      startLongPolling();
    }
    return added

若未启动长轮循，进行启动

private void startLongPolling() {
    if (!m_longPollStarted.compareAndSet(false, true)) {
      //already started
      return;
    }
    try {
      final String appId = m_configUtil.getAppId();
      final String cluster = m_configUtil.getCluster();
      final String dataCenter = m_configUtil.getDataCenter();
      final long longPollingInitialDelayInMills = m_configUtil.getLongPollingInitialDelayInMills();
      m_longPollingService.submit(new Runnable() {
        @Override
        public void run() {
          if (longPollingInitialDelayInMills > 0) {
            try {
              logger.debug("Long polling will start in {} ms.", longPollingInitialDelayInMills);
              TimeUnit.MILLISECONDS.sleep(longPollingInitialDelayInMills);
            } catch (InterruptedException e) {
              //ignore
            }
          }
          doLongPollingRefresh(appId, cluster, dataCenter);
        }
      });
    } catch (Throwable ex) {
      m_longPollStarted.set(false);
      ApolloConfigException exception =
          new ApolloConfigException("Schedule long polling refresh failed", ex);
      Tracer.logError(exception);
      logger.warn(ExceptionUtil.getDetailMessage(exception));
    }

private void doLongPollingRefresh(String appId, String cluster, String dataCenter) {
    final Random random = new Random();
    ServiceDTO lastServiceDto = null;
//	  循环执行，直到停止或线程中断
    while (!m_longPollingStopped.get() && !Thread.currentThread().isInterrupted()) {
      if (!m_longPollRateLimiter.tryAcquire(5, TimeUnit.SECONDS)) {
        //wait at most 5 seconds
        try {
          TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
        }
      }
      Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "pollNotification");
      String url = null;
      try {
        if (lastServiceDto == null) {
        	//获取所有的ConfigServer地址
          List<ServiceDTO> configServices = getConfigServices();
          lastServiceDto = configServices.get(random.nextInt(configServices.size()));
        }
//		组装url（notifications/v2）
        url =
            assembleLongPollRefreshUrl(lastServiceDto.getHomepageUrl(), appId, cluster, dataCenter,
                m_notifications);
 
        logger.debug("Long polling from {}", url);
        HttpRequest request = new HttpRequest(url);
        request.setReadTimeout(LONG_POLLING_READ_TIMEOUT);
 
        transaction.addData("Url", url);
 
        final HttpResponse<List<ApolloConfigNotification>> response =
            m_httpUtil.doGet(request, m_responseType);
 
        logger.debug("Long polling response: {}, url: {}", response.getStatusCode(), url);
        if (response.getStatusCode() == 200 && response.getBody() != null) {
          updateNotifications(response.getBody());
          updateRemoteNotifications(response.getBody());
          transaction.addData("Result", response.getBody().toString());
          //通知对应的RemoteConfigRepository
          notify(lastServiceDto, response.getBody());
        }
 
        //try to load balance
        if (response.getStatusCode() == 304 && random.nextBoolean()) {
          lastServiceDto = null;
        }
 
        m_longPollFailSchedulePolicyInSecond.success();
        transaction.addData("StatusCode", response.getStatusCode());
        transaction.setStatus(Transaction.SUCCESS);
      } catch (Throwable ex) {
        lastServiceDto = null;
        Tracer.logEvent("ApolloConfigException", ExceptionUtil.getDetailMessage(ex));
        transaction.setStatus(ex);
        long sleepTimeInSecond = m_longPollFailSchedulePolicyInSecond.fail();
        logger.warn(
            "Long polling failed, will retry in {} seconds. appId: {}, cluster: {}, namespaces: {}, long polling url: {}, reason: {}",
            sleepTimeInSecond, appId, cluster, assembleNamespaces(), url, ExceptionUtil.getDetailMessage(ex));
        try {
          TimeUnit.SECONDS.sleep(sleepTimeInSecond);
        } catch (InterruptedException ie) {
          //ignore
        }
      } finally {
        transaction.complete();
      }
    }
  }
 通知第1不注册的RemoteConfigRepository

private void notify(ServiceDTO lastServiceDto, List<ApolloConfigNotification> notifications) {
    if (notifications == null || notifications.isEmpty()) {
      return;
    }
    for (ApolloConfigNotification notification : notifications) {
      String namespaceName = notification.getNamespaceName();
      //create a new list to avoid ConcurrentModificationException
      List<RemoteConfigRepository> toBeNotified =
          Lists.newArrayList(m_longPollNamespaces.get(namespaceName));
      ApolloNotificationMessages originalMessages = m_remoteNotificationMessages.get(namespaceName);
      ApolloNotificationMessages remoteMessages = originalMessages == null ? null : originalMessages.clone();
      //since .properties are filtered out by default, so we need to check if there is any listener for it
      toBeNotified.addAll(m_longPollNamespaces
          .get(String.format("%s.%s", namespaceName, ConfigFileFormat.Properties.getValue())));
      for (RemoteConfigRepository remoteConfigRepository : toBeNotified) {
        try {
          remoteConfigRepository.onLongPollNotified(lastServiceDto, remoteMessages);
        } catch (Throwable ex) {
          Tracer.logError(ex);
        }
      }
    }
  }
 remoteConfigRepository.onLongPollNotified

public void onLongPollNotified(ServiceDTO longPollNotifiedServiceDto, ApolloNotificationMessages remoteMessages) {
    m_longPollServiceDto.set(longPollNotifiedServiceDto);
    m_remoteMessages.set(remoteMessages);
    m_executorService.submit(new Runnable() {
      @Override
      public void run() {
        m_configNeedForceRefresh.set(true);
        trySync();
      }
    });

# 小结
ConfigController：configs/{appId}/{clusterName}/{namespace}：提供配置读取功能

# 参考资料和推荐阅读
1.链接: [参考资料](https://blog.youkuaiyun.com/a934079371/article/details/109376370).