[从源码学设计]蚂蚁金服SOFARegistry之延迟操作

SOFARegistry 是蚂蚁金服开源的一个生产级、高时效、高可用的服务注册中心。
本系列文章重点在于分析设计和架构，即利用多篇文章，从多个角度反推总结 DataServer 或者 SOFARegistry 的实现机制和架构思路，让大家借以学习阿里如何设计。
本文为第十七篇，介绍SOFARegistry的延迟操作。

[从源码学设计]蚂蚁金服SOFARegistry之延迟操作

0x00 摘要

SOFARegistry 是蚂蚁金服开源的一个生产级、高时效、高可用的服务注册中心。

本系列文章重点在于分析设计和架构，即利用多篇文章，从多个角度反推总结 DataServer 或者 SOFARegistry 的实现机制和架构思路，让大家借以学习阿里如何设计。

本文为第十七篇，介绍SOFARegistry的延迟操作。

0x01 业务领域

1.1 业务缘由

为什么要有AfterWorkingProcess？

AfterWorkingProcess 的作用是延迟操作。猜测大致是因为某些情况下，无法执行业务，只能在后续时机进行弥补。

在官方博客有类似论述也支持我们的判断：

在数据未同步完成之前，所有对新节点的读数据操作，将转发到拥有该数据分片的数据节点。

在数据未同步完成之前，禁止对新节点的写数据操作，防止在数据同步过程中出现新的数据不一致情况。

1.2 学习方向

可以看到类似这种业务上延迟操作应该如何实现。

0x02 实现

2.1 定义

接口定义如下：

public interface AfterWorkingProcess {
    void afterWorkingProcess();
    int getOrder();
}

2.2 配置

这个 afterWorkProcessors 会作为 AfterWorkingProcessHandler 的成员变量进行处理。用于处理一些业务逻辑结束后的处理动作。

        @Bean(name = "afterWorkProcessors")
        public List<AfterWorkingProcess> afterWorkingProcessors() {
            List<AfterWorkingProcess> list = new ArrayList<>();
            list.add(renewDatumHandler());
            list.add(datumLeaseManager());
            list.add(disconnectEventHandler());
            list.add(notifyDataSyncHandler());
            return list;
        }

        @Bean
        public AfterWorkingProcessHandler afterWorkingProcessHandler() {
            return new AfterWorkingProcessHandler();
        }

2.3 引擎

这里用法比较少见。AfterWorkingProcessHandler 也是 AfterWorkingProcess 的实现类。

在其 afterWorkingProcess 函数中，会对 Bean afterWorkingProcessors 中间注册的实现类一一调用其 afterWorkingProcess 业务函数。

其中，getOrder 会指定执行优先级，这是一个常见套路。

public class AfterWorkingProcessHandler implements AfterWorkingProcess {

    @Resource(name = "afterWorkProcessors")
    private List<AfterWorkingProcess> afterWorkingProcessors;

    @Override
    public void afterWorkingProcess() {

        if(afterWorkingProcessors != null){
            List<AfterWorkingProcess> list = afterWorkingProcessors.stream().sorted(Comparator.comparing(AfterWorkingProcess::getOrder)).collect(Collectors.toList());

            list.forEach(AfterWorkingProcess::afterWorkingProcess);
        }
    }

    @Override
    public int getOrder() {
        return 0;
    }
}

2.4 调用

只有在 DataServerCache # updateDataServerStatus 函数中有调用：

afterWorkingProcessHandler.afterWorkingProcess();

而在 DataServerCache 中有如下函数都会调用到 updateDataServerStatus：

synced
notifiedAll
checkAndUpdateStatus
addNotWorkingServer

图示如下：

+------------------------------------------+
| DataServerCache                          |                                 +----------------------------------------------+
|                                          |                                 |   AfterWorkingProcess                        |
| synced +----------------------+          |                                 |                                              |
|                               |          | +----------------------------+  | +------------------------------------------+ |
|                               |          | | AfterWorkingProcessHandler |  | |renewDatumHandler.afterWorkingProcess     | |
|                               |          | |                            |  | |                                          | |
|                               v          | |                            |  | |datumLeaseManager.afterWorkingProcess     | |
| notifiedAll +--->updateDataServerStatus +------> afterWorkingProcess +------>+                                          | |
|                                 ^   ^    | |                            |  | |disconnectEventHandler.afterWorkingProcess| |
|                                 |   |    | +----------------------------+  | |                                          | |
|                                 |   |    |                                 | |notifyDataSyncHandler.afterWorkingProcess | |
| checkAndUpdateStatus+-----------+   |    |                                 | +------------------------------------------+ |
|                                     |    |                                 +----------------------------------------------+
| addNotWorkingServer +---------------+    |
|                                          |
+------------------------------------------+

手机如下：

因为是业务关联，所以不需要什么定时，异步之类。

2.5 业务实现

2.5.1 DisconnectEventHandler

public class DisconnectEventHandler implements InitializingBean, AfterWorkingProcess {
    /**
     * a DelayQueue that contains client disconnect events
     */
    private final DelayQueue<DisconnectEvent>           EVENT_QUEUE        = new DelayQueue<>();

    @Autowired
    private SessionServerConnectionFactory              sessionServerConnectionFactory;

    @Autowired
    private DataChangeEventCenter                       dataChangeEventCenter;

    @Autowired
    private DataServerConfig                            dataServerConfig;

    @Autowired
    private DataNodeStatus                              dataNodeStatus;

    private static final int                            BLOCK_FOR_ALL_SYNC = 5000;

    private static final BlockingQueue<DisconnectEvent> noWorkQueue        = new LinkedBlockingQueue<>();
}

在receive的正常业务操作中，如果发现本身状态不是 WORKING，则把event放入 BlockingQueue 之中。

public void receive(DisconnectEvent event) {
        if (event.getType() == DisconnectTypeEnum.SESSION_SERVER) {
            SessionServerDisconnectEvent sessionServerDisconnectEvent = (SessionServerDisconnectEvent) event;
                sessionServerDisconnectEvent.getProcessId());
        } else if (event.getType() == DisconnectTypeEnum.CLIENT) {
            ClientDisconnectEvent clientDisconnectEvent = (ClientDisconnectEvent) event;
        }

        if (dataNodeStatus.getStatus() != LocalServerStatusEnum.WORKING) {
            noWorkQueue.add(event);
            return;
        }
        EVENT_QUEUE.add(event);
}

当时机来到时候，系统再次调用afterWorkingProcess。这里会始终Block在noWorkQueue上，如果不为空，则会执行请求。

public void afterWorkingProcess() {
    try {
        /*
         * After the snapshot data is synchronized during startup, it is queued and then placed asynchronously into
         * DatumCache. When the notification becomes WORKING, there may be data in the queue that is not executed
         * to DatumCache. So it need to sleep for a while.
         */
        TimeUnit.MILLISECONDS.sleep(BLOCK_FOR_ALL_SYNC);

        while (!noWorkQueue.isEmpty()) {
            DisconnectEvent event = noWorkQueue.poll(1, TimeUnit.SECONDS);
            if (event != null) {
                receive(event);
            }
        }
    } 
}

图示如下：

+----------------------------------------------------------+
|                                  DisconnectEventHandler  |
|    +-------------------------+                           |
|    | receive                 |                           |
|    |                         |  NOT WORKING              |
|    | dataNodeStatus.getStatus+---------------+           |
|    |            +            |               |           |
|    |            | WORKING    |               | add       |
|    |            |            |               |           |
|    |            v            |               |           |
|    |  EVENT_QUEUE.add(event) |               |           |
|    |                         |           +---v---------+ |
|    +-------------------------+           |             | |
|                                          | noWorkQueue | |
|                                          |             | |
|    +-----------------------+             +-----+-------+ |
|    | afterWorkingProcess   |                   |         |
|    |                       |                   | poll    |
|    |                       |      NOT isEmpty  |         |
|    |     receive(event) <----------------------+         |
|    |                       |                             |
|    |                       |                             |
|    +-----------------------+                             |
+----------------------------------------------------------+

2.5.2 NotifyDataSyncHandler

DisconnectEventHandler 和 NotifyDataSyncHandler 的实现类似。

依托一个 LinkedBlockingQueue 做缓存queue。

public class NotifyDataSyncHandler extends AbstractClientHandler<NotifyDataSyncRequest> implements AfterWorkingProcess {
  
  private static final BlockingQueue<SyncDataRequestForWorking> noWorkQueue = new LinkedBlockingQueue<>();
  
}

在doHandle的正常业务操作中，如果发现本身状态不是 WORKING，则用业务逻辑SyncDataRequestForWorking 构建一个消息 SyncDataRequestForWorking，放入 LinkedBlockingQueue 之中。

@Override
public Object doHandle(Channel channel, NotifyDataSyncRequest request) {
        final Connection connection = ((BoltChannel) channel).getConnection();
        if (dataNodeStatus.getStatus() != LocalServerStatusEnum.WORKING) {
            noWorkQueue.add(new SyncDataRequestForWorking(connection, request));
            return CommonResponse.buildSuccessResponse();
        }
        executorRequest(connection, request);
        return CommonResponse.buildSuccessResponse();
}

当时机来到时候，系统再次调用afterWorkingProcess。这里会始终Block在noWorkQueue上，如果不为空，则会执行请求。

@Override
public void afterWorkingProcess() {
            while (!noWorkQueue.isEmpty()) {
                SyncDataRequestForWorking event = noWorkQueue.poll(1, TimeUnit.SECONDS);
                if (event != null) {
                    executorRequest(event.getConnection(), event.getRequest());
                }
            }
        } 
}

图示如下：

+----------------------------------------------------------+
|                                   NotifyDataSyncHandler  |
|    +-------------------------+                           |
|    | doHandle                |                           |
|    |                         |  NOT WORKING              |
|    | dataNodeStatus.getStatus+---------------+           |
|    |            +            |               |           |
|    |            | WORKING    |               | add       |
|    |            |            |               |           |
|    |            v            |               |           |
|    |     executorRequest     |               |           |
|    |                         |           +---v---------+ |
|    +-------------------------+           |             | |
|                                          | noWorkQueue | |
|                                          |             | |
|    +-----------------------+             +-----+-------+ |
|    | afterWorkingProcess   |                   |         |
|    |                       |                   | poll    |
|    |                       |      NOT isEmpty  |         |
|    |   executorRequest  <----------------------+         |
|    |                       |                             |
|    |                       |                             |
|    +-----------------------+                             |
+----------------------------------------------------------+

2.5.3 RenewDatumHandler

RenewDatumHandler 同 DatumLeaseManager 这两者很类似。并没有使用queue，只是提交一个线程。

其实现目的在注释中写的很清楚:

/* * After the snapshot data is synchronized during startup, it is queued and then placed asynchronously into * DatumCache. When the notification becomes WORKING, there may be data in the queue that is not executed * to DatumCache. So it need to sleep for a while. */

但是细节又有所不同，这两个类是同一个作者，怀疑此君在实验比较两种不同实现方式。

RenewDatumHandler 基于 ThreadPoolExecutorDataServer 来实现。

public class RenewDatumHandler extends AbstractServerHandler<RenewDatumRequest> implements
                                                                               AfterWorkingProcess {

    @Autowired
    private ThreadPoolExecutor  renewDatumProcessorExecutor;

}

renewDatumProcessorExecutor 是一个Bean，具体代码如下，ArrayBlockingQueue:是一个基于数组结构的有界阻塞队列，按FIFO原则进行排序。

@Bean(name = "renewDatumProcessorExecutor")
public ThreadPoolExecutor renewDatumProcessorExecutor(DataServerConfig dataServerConfig) {
            return new ThreadPoolExecutorDataServer("RenewDatumProcessorExecutor",
                dataServerConfig.getRenewDatumExecutorMinPoolSize(),
                dataServerConfig.getRenewDatumExecutorMaxPoolSize(), 300, TimeUnit.SECONDS,
                new ArrayBlockingQueue<>(dataServerConfig.getRenewDatumExecutorQueueSize()),
                new NamedThreadFactory("DataServer-RenewDatumProcessor-executor", true));
}

ThreadPoolExecutorDataServer 主要代码如下，就是简单继承了ThreadPoolExecutor，估计这里后续会有新功能添加，现在只是占坑：

public class ThreadPoolExecutorDataServer extends ThreadPoolExecutor {
    @Override
    public void execute(Runnable command) {
		super.execute(command);
    }
}

对于afterWorkingProcess，就是提交了一个线程，其业务是：等待一段时间，然后设置renewEnabled。

@Override
public void afterWorkingProcess() {
        renewDatumProcessorExecutor.submit(() -> {
            TimeUnit.MILLISECONDS.sleep(dataServerConfig.getRenewEnableDelaySec());
            renewEnabled.set(true);
        });
}