// 客戶端中，表示自身實(shí)例信息
// 服務(wù)端中，表示實(shí)例存在服務(wù)端注冊(cè)表中的信息
public class InstanceInfo {
    // ......  
    // 客戶端中，表示自己的真實(shí)工作狀態(tài)
    // 服務(wù)端中，表示服務(wù)發(fā)現(xiàn)時(shí)實(shí)例想要暴露給其他實(shí)例的工作狀態(tài)，不一定是實(shí)例的真實(shí)工作狀態(tài)
    private volatile InstanceStatus status = InstanceStatus.UP;
    // 覆蓋狀態(tài)，服務(wù)端可以根據(jù)一定規(guī)則匹配出 status
    // 外界修改實(shí)例在服務(wù)端中狀態(tài)（比如通過 actuator 修改狀態(tài)）就是修改覆蓋狀態(tài)
    private volatile InstanceStatus overriddenStatus = InstanceStatus.UNKNOWN;
    // 判斷實(shí)例信息在服務(wù)端中是否是臟的
    private volatile boolean isInstanceInfoDirty = false;
    // 租約信息
    private volatile LeaseInfo leaseInfo;
    // 記錄實(shí)例信息在服務(wù)端最近一次修改的時(shí)間
    private volatile Long lastUpdatedTimestamp;
    // 記錄實(shí)例信息在客戶端最近一次修改的時(shí)間
    private volatile Long lastDirtyTimestamp;
    // ......
}

public enum InstanceStatus {
    UP, // 啟動(dòng)狀態(tài)，表示實(shí)例對(duì)外正常提供服務(wù)
    DOWN, // 下線狀態(tài)，實(shí)例健康檢查失敗時(shí)修改為該狀態(tài)
    STARTING, // 啟動(dòng)中狀態(tài)，表示實(shí)例正在初始化啟動(dòng)中
    OUT_OF_SERVICE, // 停止服務(wù)狀態(tài)，表示實(shí)例不對(duì)外提供服務(wù)
    UNKNOWN; // 未知狀態(tài)
    // ......
}

public class LeaseInfo {
    public static final int DEFAULT_LEASE_RENEWAL_INTERVAL = 30;
    public static final int DEFAULT_LEASE_DURATION = 90;
    // 客戶端維護(hù)的心跳間隔時(shí)間
    private int renewalIntervalInSecs = DEFAULT_LEASE_RENEWAL_INTERVAL;
    // 客戶端維護(hù)的租約持續(xù)時(shí)間
    private int durationInSecs = DEFAULT_LEASE_DURATION;
    // 服務(wù)端維護(hù)的實(shí)例注冊(cè)時(shí)間
    private long registrationTimestamp;
    // 服務(wù)端維護(hù)的實(shí)例最近一次更新時(shí)間
    private long lastRenewalTimestamp; 
    // 服務(wù)端維護(hù)的實(shí)例過期清理時(shí)間
    private long evictionTimestamp;
    // 服務(wù)端維護(hù)的實(shí)例啟動(dòng)時(shí)間
    private long serviceUpTimestamp;
    // ......
}

public class Application {
    private static Random shuffleRandom = new Random();
    private String name;
    @XStreamOmitField
    private volatile boolean isDirty = false;
    /**
     * 保存著當(dāng)前name所指定的微服務(wù)名稱的所有InstanceInfo 實(shí)例
     */
    @XStreamImplicit
    private final Set<InstanceInfo> instances;
    private final AtomicReference<List<InstanceInfo>> shuffledInstances;
    // key:instanceId  value:InstanceInfo實(shí)例
    private final Map<String, InstanceInfo> instancesMap;

public class Applications {
    private static class VipIndexSupport {
        final AbstractQueue<InstanceInfo> instances = new ConcurrentLinkedQueue<>();
        final AtomicLong roundRobinIndex = new AtomicLong(0);
        final AtomicReference<List<InstanceInfo>> vipList = new AtomicReference<List<InstanceInfo>>(Collections.emptyList());
        public AtomicLong getRoundRobinIndex() {
            return roundRobinIndex;
        }
        public AtomicReference<List<InstanceInfo>> getVipList() {
            return vipList;
        }
    }
    private static final String STATUS_DELIMITER = "_";
    private String appsHashCode;
    private Long versionDelta;
    @XStreamImplicit
    private final AbstractQueue<Application> applications;
    // key:微服務(wù)名稱 value:Application實(shí)例
    private final Map<String, Application> appNameApplicationMap;
    private final Map<String, VipIndexSupport> virtualHostNameAppMap;
    private final Map<String, VipIndexSupport> secureVirtualHostNameAppMap;
}

public abstract class AbstractInstanceRegistry implements InstanceRegistry {
    // ......
    // 服務(wù)實(shí)例租約信息
    private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
            = new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();
    // 覆蓋狀態(tài) map
    protected final ConcurrentMap<String, InstanceStatus> overriddenInstanceStatusMap = CacheBuilder
            .newBuilder().initialCapacity(500)
            .expireAfterAccess(1, TimeUnit.HOURS)
            .<String, InstanceStatus>build().asMap();
    // 最近注冊(cè)隊(duì)列，實(shí)例注冊(cè)到服務(wù)端時(shí)添加
    // 先進(jìn)先出隊(duì)列，滿1000時(shí)移除最先添加的
    private final CircularQueue<Pair<Long, String>> recentRegisteredQueue;
    // 最近下架隊(duì)列，實(shí)例從服務(wù)端下架時(shí)添加
    // 先進(jìn)先出隊(duì)列，滿1000時(shí)移除最先添加的
    private final CircularQueue<Pair<Long, String>> recentCanceledQueue;
    // 最近變更隊(duì)列
    // 有定時(shí)任務(wù)維護(hù)的隊(duì)列，每30s執(zhí)行一次，移除添加進(jìn)該隊(duì)列超過3分鐘的實(shí)例變更信息
    private ConcurrentLinkedQueue<RecentlyChangedItem> recentlyChangedQueue = new ConcurrentLinkedQueue<RecentlyChangedItem>();
    private final ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    // 讀鎖（處理客戶端注冊(cè)、下架、狀態(tài)變更、刪除狀態(tài)時(shí)使用）
    private final Lock read = readWriteLock.readLock();
    // 寫鎖（處理客戶端拉取增量注冊(cè)表時(shí)使用）
    private final Lock write = readWriteLock.writeLock();
    // 服務(wù)端統(tǒng)計(jì)最近一分鐘預(yù)期收到客戶端實(shí)例心跳續(xù)租的請(qǐng)求數(shù)
    protected volatile int numberOfRenewsPerMinThreshold;
    // 服務(wù)端統(tǒng)計(jì)預(yù)期收到心跳續(xù)租的客戶端實(shí)例數(shù)
    protected volatile int expectedNumberOfClientsSendingRenews;
    // 響應(yīng)緩存
    // 服務(wù)端處理客戶端拉取注冊(cè)表請(qǐng)求時(shí)使用
    protected volatile ResponseCache responseCache;
    // ......
    // 處理注冊(cè)
    public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {...}
    // 處理下架
    public boolean cancel(String appName, String id, boolean isReplication) {...}
    // 具體下架處理
    protected boolean internalCancel(String appName, String id, boolean isReplication) {...}
    // 處理心跳續(xù)租
    public boolean renew(String appName, String id, boolean isReplication) {...}
    // 處理變更狀態(tài)
    public boolean statusUpdate(String appName, String id,
                                InstanceStatus newStatus, String lastDirtyTimestamp,
                                boolean isReplication) {...}
    // 處理刪除狀態(tài)
    public boolean deleteStatusOverride(String appName, String id,
                                        InstanceStatus newStatus,
                                        String lastDirtyTimestamp,
                                        boolean isReplication) {...}
    // 處理實(shí)例過期清理
    public void evict(long additionalLeaseMs) {...}
    // 處理拉取全量注冊(cè)表(本地全量注冊(cè)表 + 可能包含全部遠(yuǎn)程 region 注冊(cè)表)
    public Application getApplication(String appName, boolean includeRemoteRegion) {...}
    // 處理拉取全量注冊(cè)表(本地全量注冊(cè)表 + 可能包含指定遠(yuǎn)程 region 全量注冊(cè)表)
    public Applications getApplicationsFromMultipleRegions(String[] remoteRegions) {...}
    // 處理拉取增量注冊(cè)表(本地增量注冊(cè)表 + 可能包含指定遠(yuǎn)程 region 增量注冊(cè)表)
    public Applications getApplicationDeltasFromMultipleRegions(String[] remoteRegions) {...}
    ...... 
}

public class Lease<T> {
    // 實(shí)例下架時(shí)間
    private long evictionTimestamp;
    // 實(shí)例注冊(cè)時(shí)間
    private long registrationTimestamp;
    // 實(shí)例啟動(dòng)時(shí)間
    private long serviceUpTimestamp;
    // 實(shí)例租約過期時(shí)間
    private volatile long lastUpdateTimestamp;
    ......
}

public class ResponseCacheImpl implements ResponseCache {
    // ......
    // 只讀緩存
    private final ConcurrentMap<Key, Value> readOnlyCacheMap = new ConcurrentHashMap<Key, Value>();
    // 讀寫緩存
    // LoadingCache：Guava 提供的本地緩存，多線程的場(chǎng)景下保證只有一個(gè)線程加載相應(yīng)緩存項(xiàng)
    private final LoadingCache<Key, Value> readWriteCacheMap;
    // 判斷是否使用只讀緩存
    private final boolean shouldUseReadOnlyResponseCache;
    // ......
}

public class PeerAwareInstanceRegistryImpl extends AbstractInstanceRegistry implements PeerAwareInstanceRegistry {
    // 當(dāng)前服務(wù)端節(jié)點(diǎn)的啟動(dòng)時(shí)間
    private long startupTime = 0;
    // 判斷服務(wù)端啟動(dòng)時(shí)同步集群節(jié)點(diǎn)注冊(cè)表的實(shí)例數(shù)是否為空
    private boolean peerInstancesTransferEmptyOnStartup = true;
    // 最近一分鐘同步復(fù)制給集群節(jié)點(diǎn)的次數(shù) 
    private final MeasuredRate numberOfReplicationsLastMin;
    // 服務(wù)端的相鄰集群節(jié)點(diǎn)，配置文件中配置
    protected volatile PeerEurekaNodes peerEurekaNodes;
}

@Produces({"application/xml", "application/json"})
public class InstanceResource {
    private static final Logger logger = LoggerFactory
            .getLogger(InstanceResource.class);
    private final PeerAwareInstanceRegistry registry;
    private final EurekaServerConfig serverConfig;
    private final String id;
    private final ApplicationResource app;
    InstanceResource(ApplicationResource app, String id, EurekaServerConfig serverConfig, PeerAwareInstanceRegistry registry) {
        this.app = app;
        this.id = id;
        this.serverConfig = serverConfig;
        this.registry = registry;
    }
    ...
}