反向操作－Eurka的读写锁

//所有注册实例集合
private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
            = new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>(); 
//被修改过的实例集合,用于增量更新实例是读取
private ConcurrentLinkedQueue<RecentlyChangedItem> recentlyChangedQueue = new ConcurrentLinkedQueue<RecentlyChangedItem>();


// 注册方法使用了读锁
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication){
    read.lock();
    ...
    gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap); // 往注册表内添加实例
    ...
    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel)); //添加最近修改队列
}
// 取消实例的注册使用读锁
protected boolean internalCancel(String appName, String id, boolean isReplication) {
    read.lock();
    Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
    Lease<InstanceInfo> leaseToCancel = null;
    if (gMap != null) {
        leaseToCancel = gMap.remove(id); // 这里开始去注册表中移除 实例
    }
    .....
    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel)); //添加最近修改队列
}
//更新实例的状态。使用读锁
public boolean statusUpdate(String appName, String id,
                                InstanceStatus newStatus, String lastDirtyTimestamp,
                                boolean isReplication) {
     read.lock();
    Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
    Lease<InstanceInfo> lease = null;
    if (gMap != null) {
        lease = gMap.get(id); //获取要修改的实例
    }
    ....
    lease.serviceUp(); // 对要修改的实例进行某个状态的修改
  ....
     recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel)); //添加最近修改队列
}
// 下线状态赋值给实例
public boolean deleteStatusOverride(String appName, String id,
                                        InstanceStatus newStatus,
                                        String lastDirtyTimestamp,
                                        boolean isReplication) {
    read.lock();
    // 对实例进行状态修改 , 修改为下线状态
    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel)); //添加最近修改队列
}


//获取增量实例 (这里是用的写锁)
public Applications getApplicationDeltas(){
   Applications apps = new Applications();
    write.lock();
    ....
    Iterator<RecentlyChangedItem> iter = this.recentlyChangedQueue.iterator(); //返回最近改变的队列, 即为增量的实例
  //开始对 recentlyChangedQueue 最近改变了的队列进行遍历, 最终将改变过的实例 也就是增量返回
    ......
    return apps;
}


//获取全量实例 (这里没有加锁)
@Deprecated
public Applications getApplications(boolean includeRemoteRegion) {
    ....
    Applications apps = new Applications();
    //对注册表进行遍历
    for (Entry<String, Map<String, Lease<InstanceInfo>>> entry : registry.entrySet()) {
        Application app = null;
        if (entry.getValue() != null) {
            for (Entry<String, Lease<InstanceInfo>> stringLeaseEntry : entry.getValue().entrySet()) {
                Lease<InstanceInfo> lease = stringLeaseEntry.getValue();
              ......
                app.addInstance(decorateInstanceInfo(lease));
            }
        }
        if (app != null) {
            apps.addApplication(app);
        }
        ....
        return apps;
    }
}


//心跳机制 进行服务续约 (这里没有加锁)
public boolean renew(String appName, String id, boolean isReplication) {
    ....
    Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);//获取Lease
    .... 开始续约操作
}