Eureka的InstanceInfoReplicator类（服务注册辅助工具）

//略去不相关代码
...
//实例化InstanceInfoReplicator对象
instanceInfoReplicator = new InstanceInfoReplicator(
                    this,
                    instanceInfo,
                    clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                    2); // burstSize

            //监听器，用来监听作为Eureka client的自身的状态变化
            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);
                    }
                    //状态变化时notify方法会被执行，此时上报最新状态到Eureka server
                    instanceInfoReplicator.onDemandUpdate();
                }
            };

            if (clientConfig.shouldOnDemandUpdateStatusChange()) {
                //注册监听器
                applicationInfoManager.registerStatusChangeListener(statusChangeListener);
            }
            //服务注册
            instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());

/**
 * A task for updating and replicating the local instanceinfo to the remote server. Properties of this task are:
 * - configured with a single update thread to guarantee sequential update to the remote server
 * - update tasks can be scheduled on-demand via onDemandUpdate()
 * - task processing is rate limited by burstSize
 * - a new update task is always scheduled automatically after an earlier update task. However if an on-demand task
 *   is started, the scheduled automatic update task is discarded (and a new one will be scheduled after the new
 *   on-demand update).
 *
 *   @author dliu
 */

InstanceInfoReplicator(DiscoveryClient discoveryClient, InstanceInfo instanceInfo, int replicationIntervalSeconds, int burstSize) {
        this.discoveryClient = discoveryClient;
        this.instanceInfo = instanceInfo;
		//线程池，core size为1，使用DelayedWorkQueue队列
        this.scheduler = Executors.newScheduledThreadPool(1,
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-InstanceInfoReplicator-%d")
                        .setDaemon(true)
                        .build());

        this.scheduledPeriodicRef = new AtomicReference<Future>();

        this.started = new AtomicBoolean(false);
        //RateLimiter是个限制频率的工具类，用来限制单位时间内的任务次数
        this.rateLimiter = new RateLimiter(TimeUnit.MINUTES);
        this.replicationIntervalSeconds = replicationIntervalSeconds;
        this.burstSize = burstSize;
        //通过周期间隔，和burstSize参数，计算每分钟允许的任务数
        this.allowedRatePerMinute = 60 * this.burstSize / this.replicationIntervalSeconds;
        logger.info("InstanceInfoReplicator onDemand update allowed rate per min is {}", allowedRatePerMinute);
    }

public void start(int initialDelayMs) {
		//CAS操作，不但保证了只执行一次，多线程场景也能保证
		if (started.compareAndSet(false, true)) {
		        instanceInfo.setIsDirty();  // for initial register
		        //提交一个任务，延时执行，注意第一个参数是this，因此延时结束时，InstanceInfoReplicator的run方法会被执行
		        Future next = scheduler.schedule(this, initialDelayMs, TimeUnit.SECONDS);
		        //这个任务的Feature对象放在成员变量scheduledPeriodicRef中
		        scheduledPeriodicRef.set(next);
		}
}

public void run() {
        try {
            //更新信息，用于稍后的上报
            discoveryClient.refreshInstanceInfo();

            Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
            if (dirtyTimestamp != null) {
                //上报
                discoveryClient.register();
                instanceInfo.unsetIsDirty(dirtyTimestamp);
            }
        } catch (Throwable t) {
            logger.warn("There was a problem with the instance info replicator", t);
        } finally {
            //每次执行完毕都会创建一个延时执行的任务，就这样实现了周期性执行的逻辑
            Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
            //每次创建的周期性任务，都要放入scheduledPeriodicRef，
            //如果外部调用了onDemandUpdate，就能通过onDemandUpdate取得当前要执行的任务
            scheduledPeriodicRef.set(next);
        }
    }

public boolean onDemandUpdate() {
        //没有达到频率限制才会执行
        if (rateLimiter.acquire(burstSize, allowedRatePerMinute)) {
            //提交一个任务
            scheduler.submit(new Runnable() {
                @Override
                public void run() {
                    logger.debug("Executing on-demand update of local InstanceInfo");
                    //取出之前已经提交的任务
                    Future latestPeriodic = scheduledPeriodicRef.get();
                    //如果此任务未完成，就立即取消
                    if (latestPeriodic != null && !latestPeriodic.isDone()) {
                        logger.debug("Canceling the latest scheduled update, it will be rescheduled at the end of on demand update");
                        latestPeriodic.cancel(false);
                    }
					//通过调用run方法，令任务在延时后执行，相当于周期性任务中的一次
                    InstanceInfoReplicator.this.run();
                }
            });
            return true;
        } else {
            //如果超过了设置的频率限制，本次onDemandUpdate方法就提交任务了
            logger.warn("Ignoring onDemand update due to rate limiter");
            return false;
        }
    }