Eureka 客户端源码分析(下)

我们看下com.netflix.discovery.DiscoveryClient这个类，这个类在应用启动的时候被加载到容器中，肯定会调用构造方法

构造方法如下：

    @Inject
    DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
                    Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
        
        //一系列的配置
	......

        try {
	    下面是几个线程池的创建
            // default size of 2 - 1 each for heartbeat and cacheRefresh
            scheduler = Executors.newScheduledThreadPool(2,
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-%d")
                            .setDaemon(true)
                            .build());
	    //心跳线程池(维持当前应用续约的线程池，用来持续发送心跳请求)
            heartbeatExecutor = new ThreadPoolExecutor(
                    1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                    new SynchronousQueue<Runnable>(),
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                            .setDaemon(true)
                            .build()
            );  // use direct handoff

            cacheRefreshExecutor = new ThreadPoolExecutor(
                    1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                    new SynchronousQueue<Runnable>(),
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                            .setDaemon(true)
                            .build()
            );  // use direct handoff

           
        // 重要方法在这里 finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
        initScheduledTasks();

        try {
            Monitors.registerObject(this);
        } catch (Throwable e) {
            logger.warn("Cannot register timers", e);
        }

        ......
    }


    /**
     * Initializes all scheduled tasks.
     */
    private void initScheduledTasks() {
        if (clientConfig.shouldFetchRegistry()) {
            // registry cache refresh timer
            int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
            int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
            //1、执行刷新任务的定时器
	    cacheRefreshTask = new TimedSupervisorTask(
                    "cacheRefresh",
                    scheduler,
                    cacheRefreshExecutor,
                    registryFetchIntervalSeconds,
                    TimeUnit.SECONDS,
                    expBackOffBound,
		    //线程任务在这里，主要是为了执行这个线程的run方法
                    new CacheRefreshThread() //在1)中继续详细介绍
            );
            scheduler.schedule(
                    cacheRefreshTask,
                    registryFetchIntervalSeconds, TimeUnit.SECONDS);
        }

	//2、客户端默认注册到eureka，shouldRegisterWithEureka()默认为true
        if (clientConfig.shouldRegisterWithEureka()) {
            int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
            int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
            logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);

            //3、执行定时任务 Heartbeat timer
            heartbeatTask = new TimedSupervisorTask(
                    "heartbeat",
                    scheduler,
                    heartbeatExecutor,
                    renewalIntervalInSecs,
                    TimeUnit.SECONDS,
                    expBackOffBound,
                    //主要执行线程的run方法
                    new HeartbeatThread() //在2) 中详细介绍
            );
            scheduler.schedule(
                    heartbeatTask,
                    renewalIntervalInSecs, TimeUnit.SECONDS);

            // 获得当前注册服务的基本信息
            instanceInfoReplicator = new InstanceInfoReplicator(
                    this,
                    instanceInfo,
                    clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                    2); // burstSize

           
	    //4、将当前服务注册到注册中心。 在3)中详细介绍
            instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
        } else {
            logger.info("Not registering with Eureka server per configuration");
        }
    }

　　

1）CacheRefreshThread执行刷新任务的线程

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

        try {
            // If the delta is disabled or if it is the first time, get all
            // applications
            Applications applications = getApplications();

            if (clientConfig.shouldDisableDelta()
                    || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
                    || forceFullRegistryFetch
                    || (applications == null)
                    || (applications.getRegisteredApplications().size() == 0)
                    || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
            {
               ......
		//主要执行这个方法（发送HTTP请求到注册中心来获取注册信息，并缓存到本地）
	       getAndStoreFullRegistry();
            } else {
                getAndUpdateDelta(applications);
            }
            applications.setAppsHashCode(applications.getReconcileHashCode());
            logTotalInstances();
        } catch (Throwable e) {
            logger.error(PREFIX + "{} - was unable to refresh its cache! status = {}", appPathIdentifier, e.getMessage(), e);
            return false;
        } finally {
            if (tracer != null) {
                tracer.stop();
            }
        }

        // Notify about cache refresh before updating the instance remote status
        onCacheRefreshed();

        // Update remote status based on refreshed data held in the cache
        updateInstanceRemoteStatus();

        // registry was fetched successfully, so return true
        return true;
    }

　　

2) HeartbeatThread执行心跳续约任务的线程

    private class HeartbeatThread implements Runnable {

        public void run() {
            if (renew()) {
                lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
            }
        }
    }

  // 续约任务
  boolean renew() {
        EurekaHttpResponse<InstanceInfo> httpResponse;
        try {
	    //1、发送HTTP请求到注册中心
            httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
            logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
	    //2、如果请求响应失败，则重新调用注册方法
            if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {
                REREGISTER_COUNTER.increment();
                logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
                long timestamp = instanceInfo.setIsDirtyWithTime();
                boolean success = register();
                if (success) {
                    instanceInfo.unsetIsDirty(timestamp);
                }
                return success;
            }
            return httpResponse.getStatusCode() == Status.OK.getStatusCode();
        } catch (Throwable e) {
            logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
            return false;
        }
    }

　　

3)instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds()); 发送请求到注册中心

 public void start(int initialDelayMs) {
        if (started.compareAndSet(false, true)) {
            instanceInfo.setIsDirty();  // for initial register
            //启动一个定时任务，任务执行this。
	    //真正执行的是class InstanceInfoReplicator的run方法
	    Future next = scheduler.schedule(this, initialDelayMs, TimeUnit.SECONDS);
            scheduledPeriodicRef.set(next);
        }
    }

//InstanceInfoReplicator的run方法
    public void run() {
        try {
            discoveryClient.refreshInstanceInfo();

            Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
            if (dirtyTimestamp != null) {
		//真正的注册实现。也就是发送HTTP请求到注册中心
                discoveryClient.register();
                instanceInfo.unsetIsDirty(dirtyTimestamp);
            }
        } catch (Throwable t) {
            logger.warn("There was a problem with the instance info replicator", t);
        } finally {
            Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
            scheduledPeriodicRef.set(next);
        }
    }

　　 总结：由以上代码分析可知，在DiscoveryClient被创建的时候，在其构造方法中，启动了三个线程池，

    然后分别启动了三个定时器任务：注册当前服务到注册中心；持续发送心跳进行续约任务；定时刷新注册中心注册细信息到本地

参考：Eureka源码深度解析

@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
                Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
    if (args != null) {
        this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
        this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
        this.eventListeners.addAll(args.getEventListeners());
        this.preRegistrationHandler = args.preRegistrationHandler;
    } else {
        this.healthCheckCallbackProvider = null;
        this.healthCheckHandlerProvider = null;
        this.preRegistrationHandler = null;
    }
    
    this.applicationInfoManager = applicationInfoManager;
    InstanceInfo myInfo = applicationInfoManager.getInfo();

    clientConfig = config;
    staticClientConfig = clientConfig;
    transportConfig = config.getTransportConfig();
    instanceInfo = myInfo;
    if (myInfo != null) {
        appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
    } else {
        logger.warn("Setting instanceInfo to a passed in null value");
    }

    this.backupRegistryProvider = backupRegistryProvider;
    this.endpointRandomizer = endpointRandomizer;
    this.urlRandomizer = new EndpointUtils.InstanceInfoBasedUrlRandomizer(instanceInfo);
    localRegionApps.set(new Applications());

    fetchRegistryGeneration = new AtomicLong(0);

    remoteRegionsToFetch = new AtomicReference<String>(clientConfig.fetchRegistryForRemoteRegions());
    remoteRegionsRef = new AtomicReference<>(remoteRegionsToFetch.get() == null ? null : remoteRegionsToFetch.get().split(","));

    if (config.shouldFetchRegistry()) {
        this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
    } else {
        this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
    }

    if (config.shouldRegisterWithEureka()) {
        this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
    } else {
        this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
    }

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

    if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
        logger.info("Client configured to neither register nor query for data.");
        scheduler = null;
        heartbeatExecutor = null;
        cacheRefreshExecutor = null;
        eurekaTransport = null;
        instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());

        // This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
        // to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
        DiscoveryManager.getInstance().setEurekaClientConfig(config);

        initTimestampMs = System.currentTimeMillis();
        logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
                initTimestampMs, this.getApplications().size());

        return;  // no need to setup up an network tasks and we are done
}

    try {
        // default size of 2 - 1 each for heartbeat and cacheRefresh
scheduler = Executors.newScheduledThreadPool(2,
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-%d")
                        .setDaemon(true)
                        .build());

        heartbeatExecutor = new ThreadPoolExecutor(
                1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

cacheRefreshExecutor = new ThreadPoolExecutor(
                1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

eurekaTransport = new EurekaTransport();
        scheduleServerEndpointTask(eurekaTransport, args);

        AzToRegionMapper azToRegionMapper;
        if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
            azToRegionMapper = new DNSBasedAzToRegionMapper(clientConfig);
        } else {
            azToRegionMapper = new PropertyBasedAzToRegionMapper(clientConfig);
        }
        if (null != remoteRegionsToFetch.get()) {
            azToRegionMapper.setRegionsToFetch(remoteRegionsToFetch.get().split(","));
        }
        instanceRegionChecker = new InstanceRegionChecker(azToRegionMapper, clientConfig.getRegion());
    } catch (Throwable e) {
        throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
    }

    if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
        fetchRegistryFromBackup();
    }

    // call and execute the pre registration handler before all background tasks (inc registration) is started
if (this.preRegistrationHandler != null) {
        this.preRegistrationHandler.beforeRegistration();
    }

    if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
        try {
            if (!register() ) {
                throw new IllegalStateException("Registration error at startup. Invalid server response.");
            }
        } catch (Throwable th) {
            logger.error("Registration error at startup: {}", th.getMessage());
            throw new IllegalStateException(th);
        }
    }

    // finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
initScheduledTasks();

    try {
        Monitors.registerObject(this);
    } catch (Throwable e) {
        logger.warn("Cannot register timers", e);
    }

    // This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
    // to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
    DiscoveryManager.getInstance().setEurekaClientConfig(config);

    initTimestampMs = System.currentTimeMillis();
    logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
            initTimestampMs, this.getApplications().size());
}