@Override
    public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
        // Renewals happen every 30 seconds and for a minute it should be a factor of 2.
        this.expectedNumberOfClientsSendingRenews = count;
        updateRenewsPerMinThreshold();
        logger.info("Got {} instances from neighboring DS node", count);
        logger.info("Renew threshold is: {}", numberOfRenewsPerMinThreshold);
        this.startupTime = System.currentTimeMillis();
        if (count > 0) {
            this.peerInstancesTransferEmptyOnStartup = false;
        }
        DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
        boolean isAws = Name.Amazon == selfName;
        if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {
            logger.info("Priming AWS connections for all replicas..");
            primeAwsReplicas(applicationInfoManager);
        }
        logger.info("Changing status to UP");
        applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
        super.postInit();
    }

protected void updateRenewsPerMinThreshold() {
        this.numberOfRenewsPerMinThreshold = (int) (this.expectedNumberOfClientsSendingRenews
                * (60.0 / serverConfig.getExpectedClientRenewalIntervalSeconds())
                * serverConfig.getRenewalPercentThreshold());
    }

protected void postInit() {
        renewsLastMin.start();
        if (evictionTaskRef.get() != null) {
            evictionTaskRef.get().cancel();
        }
        evictionTaskRef.set(new EvictionTask());
        evictionTimer.schedule(evictionTaskRef.get(),
                serverConfig.getEvictionIntervalTimerInMs(),
                serverConfig.getEvictionIntervalTimerInMs());
    }

private final long sampleInterval;  //1分鐘  
 
  public synchronized void start() {
        if (!isActive) {
            timer.schedule(new TimerTask() {
 
                @Override
                public void run() {
                    try {
                        // Zero out the current bucket.
                        //每分鐘這塊調(diào)度異常
                        //currentBucket 是用來更新當(dāng)前這一分鐘的次數(shù)的
                        //lastBucket 是保留了上一分鐘的心跳次數(shù)
                        //timer調(diào)度任務(wù)，1分鐘來一次，就將上一分鐘的心跳次數(shù)設(shè)置到lastBucket中去
                        lastBucket.set(currentBucket.getAndSet(0));
                    } catch (Throwable e) {
                        logger.error("Cannot reset the Measured Rate", e);
                    }
                }
            }, sampleInterval, sampleInterval);
 
            isActive = true;
        }
    }

/* visible for testing */ class EvictionTask extends TimerTask {
 
        private final AtomicLong lastExecutionNanosRef = new AtomicLong(0l);
 
        @Override
        public void run() {
            try {
                long compensationTimeMs = getCompensationTimeMs();
                logger.info("Running the evict task with compensationTime {}ms", compensationTimeMs);
                evict(compensationTimeMs);
            } catch (Throwable e) {
                logger.error("Could not run the evict task", e);
            }
        }
 
        /**
         * compute a compensation time defined as the actual time this task was executed since the prev iteration,
         * vs the configured amount of time for execution. This is useful for cases where changes in time (due to
         * clock skew or gc for example) causes the actual eviction task to execute later than the desired time
         * according to the configured cycle.
         */
        //比預(yù)期的時間晚
        long getCompensationTimeMs() {
            //先獲取當(dāng)前時間
            long currNanos = getCurrentTimeNano();
            //上一次這個EvictionTask被執(zhí)行的時間。
            long lastNanos = lastExecutionNanosRef.getAndSet(currNanos);
            if (lastNanos == 0l) {
                return 0l;
            }
 
            long elapsedMs = TimeUnit.NANOSECONDS.toMillis(currNanos - lastNanos);
            long compensationTime = elapsedMs - serverConfig.getEvictionIntervalTimerInMs();
            return compensationTime <= 0l ? 0l : compensationTime;
        }
 
        long getCurrentTimeNano() {  // for testing
            return System.nanoTime();
        }
 
    }

public void evict(long additionalLeaseMs) {
        logger.debug("Running the evict task");
 
        //是否運行主動刪除故障的實例，自我保護機制有關(guān)
        if (!isLeaseExpirationEnabled()) {
            logger.debug("DS: lease expiration is currently disabled.");
            return;
        }
 
        // We collect first all expired items, to evict them in random order. For large eviction sets,
        // if we do not that, we might wipe out whole apps before self preservation kicks in. By randomizing it,
        // the impact should be evenly distributed across all applications.
        List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();
        for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) {
            Map<String, Lease<InstanceInfo>> leaseMap = groupEntry.getValue();
            if (leaseMap != null) {
                for (Entry<String, Lease<InstanceInfo>> leaseEntry : leaseMap.entrySet()) {
                    Lease<InstanceInfo> lease = leaseEntry.getValue();
                    //如果超過3分鐘加上補償時間，就認為故障了
                    if (lease.isExpired(additionalLeaseMs) && lease.getHolder() != null) {
                        expiredLeases.add(lease);
                    }
                }
            }
        }
 
        // To compensate for GC pauses or drifting local time, we need to use current registry size as a base for
        // triggering self-preservation. Without that we would wipe out full registry.
 
        //20
        int registrySize = (int) getLocalRegistrySize();
        // 20*0.85
        int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
        //3
        int evictionLimit = registrySize - registrySizeThreshold;
 
        int toEvict = Math.min(expiredLeases.size(), evictionLimit);
        if (toEvict > 0) {
            logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);
 
            Random random = new Random(System.currentTimeMillis());
            //隨機挑選3個服務(wù)
            for (int i = 0; i < toEvict; i++) {
                // Pick a random item (Knuth shuffle algorithm)
                int next = i + random.nextInt(expiredLeases.size() - i);
                Collections.swap(expiredLeases, i, next);
                Lease<InstanceInfo> lease = expiredLeases.get(i);
 
                String appName = lease.getHolder().getAppName();
                String id = lease.getHolder().getId();
                EXPIRED.increment();
                logger.warn("DS: Registry: expired lease for {}/{}", appName, id);
                //對這個隨機挑選出來的，這個也是shutdown方法調(diào)用的
                internalCancel(appName, id, false);
            }
        }
    }

public boolean isExpired(long additionalLeaseMs) {
        //當(dāng)前時間是否大于上一次心跳時間加上90s+再加上補償時間
        return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
    }