// 打印日志
logger.info("Initializing Eureka in region {}", this.clientConfig.getRegion());
// 配置文件中的register-with-eureka和fetch-registry如果都为false则不注册和拉去服务列表了
if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
	logger.info("Client configured to neither register nor query for data.");
	this.scheduler = null;
	this.heartbeatExecutor = null;
	this.cacheRefreshExecutor = null;
	this.eurekaTransport = null;
	this.instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), this.clientConfig.getRegion());
	DiscoveryManager.getInstance().setDiscoveryClient(this);
	DiscoveryManager.getInstance().setEurekaClientConfig(config);
	this.initTimestampMs = System.currentTimeMillis();
	logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}", this.initTimestampMs, this.getApplications().size());
} else {

logger.info("Initializing Eureka in region {}", this.clientConfig.getRegion());

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
	Stopwatch tracer = this.FETCH_REGISTRY_TIMER.start();

	label122: {
		boolean var4;
		try {
            Applications applications = this.getApplications();
            // 如果增量式拉取被禁止，或者Applications为null，进行全量拉取
			if (!this.clientConfig.shouldDisableDelta() && Strings.isNullOrEmpty(this.clientConfig.getRegistryRefreshSingleVipAddress()) && !forceFullRegistryFetch && applications != null && applications.getRegisteredApplications().size() != 0 && applications.getVersion() != -1L) {
				this.getAndUpdateDelta(applications);
			} else {
				logger.info("Disable delta property : {}", this.clientConfig.shouldDisableDelta());
				logger.info("Single vip registry refresh property : {}", this.clientConfig.getRegistryRefreshSingleVipAddress());
				logger.info("Force full registry fetch : {}", forceFullRegistryFetch);
				logger.info("Application is null : {}", applications == null);
				logger.info("Registered Applications size is zero : {}", applications.getRegisteredApplications().size() == 0);
                logger.info("Application version is -1: {}", applications.getVersion() == -1L);
                // 全量拉取注册表信息
				this.getAndStoreFullRegistry();
			}

			applications.setAppsHashCode(applications.getReconcileHashCode());
			this.logTotalInstances();
			break label122;
		} catch (Throwable var8) {
			logger.error("DiscoveryClient_{} - was unable to refresh its cache! status = {}", new Object[]{this.appPathIdentifier, var8.getMessage(), var8});
			var4 = false;
		} finally {
			if (tracer != null) {
				tracer.stop();
			}

		}

		return var4;
	}

	this.onCacheRefreshed();
	this.updateInstanceRemoteStatus();
	return true;
}

// 这里的urlPath传入的是/apps
WebResource webResource = this.jerseyClient.resource(this.serviceUrl).path(urlPath);

public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
	try {
        read.lock();
        // 根据appName对服务实例集群进行分类
		Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
		REGISTER.increment(isReplication);
		if (gMap == null) {
			final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap<String, Lease<InstanceInfo>>();
			gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
			if (gMap == null) {
				gMap = gNewMap;
			}
        }
        // 根据实例id获取实例的租约
		Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
		// Retain the last dirty timestamp without overwriting it, if there is already a lease
		if (existingLease != null && (existingLease.getHolder() != null)) {
			Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp();
			Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
			logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);

			// this is a > instead of a >= because if the timestamps are equal, we still take the remote transmitted
			// InstanceInfo instead of the server local copy.
			if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) {
				logger.warn("There is an existing lease and the existing lease's dirty timestamp {} is greater" +
						" than the one that is being registered {}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
				logger.warn("Using the existing instanceInfo instead of the new instanceInfo as the registrant");
				registrant = existingLease.getHolder();
			}
		} else {
            // The lease does not exist and hence it is a new registration
            // 如果租约不存在，这是一个新的注册实例
			synchronized (lock) {
				if (this.expectedNumberOfRenewsPerMin > 0) {
					// Since the client wants to cancel it, reduce the threshold
					// (1
                    // for 30 seconds, 2 for a minute)
                    // 自我保护机制
					this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2;
					this.numberOfRenewsPerMinThreshold =
							(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
				}
			}
			logger.debug("No previous lease information found; it is new registration");
        }
        // 创建新的租约
		Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
		if (existingLease != null) {
			lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
		}
		gMap.put(registrant.getId(), lease);
		synchronized (recentRegisteredQueue) {
			recentRegisteredQueue.add(new Pair<Long, String>(
					System.currentTimeMillis(),
					registrant.getAppName() + "(" + registrant.getId() + ")"));
		}
		// This is where the initial state transfer of overridden status happens
		if (!InstanceStatus.UNKNOWN.equals(registrant.getOverriddenStatus())) {
			logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
							+ "overrides", registrant.getOverriddenStatus(), registrant.getId());
			if (!overriddenInstanceStatusMap.containsKey(registrant.getId())) {
				logger.info("Not found overridden id {} and hence adding it", registrant.getId());
				overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
			}
		}
		InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(registrant.getId());
		if (overriddenStatusFromMap != null) {
			logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
			registrant.setOverriddenStatus(overriddenStatusFromMap);
		}

		// Set the status based on the overridden status rules
		InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(registrant, existingLease, isReplication);
		registrant.setStatusWithoutDirty(overriddenInstanceStatus);

		// If the lease is registered with UP status, set lease service up timestamp
		if (InstanceStatus.UP.equals(registrant.getStatus())) {
			lease.serviceUp();
		}
		registrant.setActionType(ActionType.ADDED);
		recentlyChangedQueue.add(new RecentlyChangedItem(lease));
		registrant.setLastUpdatedTimestamp();
		invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
		logger.info("Registered instance {}/{} with status {} (replication={})",
				registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
	} finally {
		read.unlock();
	}
}