@Bean
public DiscoveryClient discoveryClient(EurekaInstanceConfig config, EurekaClient client) {
  return new EurekaDiscoveryClient(config, client);
}

@Bean(destroyMethod = "shutdown")
@ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
@org.springframework.cloud.context.config.annotation.RefreshScope
@Lazy
public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance) {
  manager.getInfo(); // force initialization
  return new CloudEurekaClient(manager, config, this.optionalArgs,this.context);
}

  private void initScheduledTasks() {
    //獲取服務(wù)注冊列表信息
    if (clientConfig.shouldFetchRegistry()) {
      //服務(wù)注冊列表更新的周期時間
      int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
      int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
      //定時更新服務(wù)注冊列表
      scheduler.schedule(
          new TimedSupervisorTask(
              "cacheRefresh",
              scheduler,
              cacheRefreshExecutor,
              registryFetchIntervalSeconds,
              TimeUnit.SECONDS,
              expBackOffBound,
              new CacheRefreshThread() //該線程執(zhí)行更新的具體邏輯
          ),
          registryFetchIntervalSeconds, TimeUnit.SECONDS);
    }
    if (clientConfig.shouldRegisterWithEureka()) {
      //服務(wù)續(xù)約的周期時間
      int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
      int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
      //應(yīng)用啟動可見此日志，內(nèi)容是：Starting heartbeat executor: renew interval is: 30
      logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
      // 定時續(xù)約
      scheduler.schedule(
          new TimedSupervisorTask(
              "heartbeat",
              scheduler,
              heartbeatExecutor,
              renewalIntervalInSecs,
              TimeUnit.SECONDS,
              expBackOffBound,
              new HeartbeatThread() //該線程執(zhí)行續(xù)約的具體邏輯
          ),
          renewalIntervalInSecs, TimeUnit.SECONDS);

      //這個Runable中含有服務(wù)注冊的邏輯
      instanceInfoReplicator = new InstanceInfoReplicator(
          this,
          instanceInfo,
          clientConfig.getInstanceInfoReplicationIntervalSeconds(),
          2); // burstSize

      statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
        @Override
        public String getId() {
          return "statusChangeListener";
        }

        @Override
        public void notify(StatusChangeEvent statusChangeEvent) {
          if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
              InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {
            // log at warn level if DOWN was involved
            logger.warn("Saw local status change event {}", statusChangeEvent);
          } else {
            logger.info("Saw local status change event {}", statusChangeEvent);
          }
          instanceInfoReplicator.onDemandUpdate();
        }
      };

      if (clientConfig.shouldOnDemandUpdateStatusChange()) {
        applicationInfoManager.registerStatusChangeListener(statusChangeListener);
      }
      //服務(wù)注冊
      instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
    } else {
      logger.info("Not registering with Eureka server per configuration");
    }
  }