rocketmq源码简析之namesrc模块

先看一下官网一张清晰的架构图：

nameserver作为替换早期版本zookeeper的轻量级实现，它只实现了zk的一致性+发布订阅，当然实现方式是不一样的。它的一致性是通过每个节点的Broker、Consumer、Producer定时心跳同步的，存在短暂的不一致性，可以说是弱一致性，不会有影响，因为有柔性事务保证重试机制。发布订阅跟zk就差不多了，Broker会与每一台nameserver保持tcp连接，上传topic信息，自身健康状态，filter信息等；Consumer和Producer会与一台nameserver保持tcp连接，获取路由信息，保证负载均衡。

接下来重点看一下nameserver相关代码：
启动类NamesrvStartup main0方法，通过解析命令行参数，比如c后面配置配置文件，封装到namesrvConfig和nettyServerConfig，来构建NamesrvController这个真正的启动控制器。
NamesrvController有几个重要属性

    //namesrv相关参数 private final NamesrvConfig namesrvConfig;    //netty相关参数    private final NettyServerConfig nettyServerConfig;    //单线程池，此线程用来启动namesrc，启动之后还有2个定时线程来scanNotActiveBroker（清理不生效broker）和printAllPeriodically（打印每个namesrv的配置表）    private final ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(new ThreadFactoryImpl(        "NSScheduledThread"));    //namesrv配置管理器，容器为HashMap<String/* Namespace */, HashMap<String/* Key */, String/* Value */>> configTable，ReadWriteLock保证读写安全    private final KVConfigManager kvConfigManager;    //所有运行数据管理器，topicqueuetable、brokeraddrtable等，信息量很多，ReadWriteLock保证读写安全    private final RouteInfoManager routeInfoManager;//服务启动接口，这里传入的是NettyRemotingServer，用netty启动，是rocketmq remoting模块，包括注册请求处理器DefaultRequestProcessor，以及几种数据传输方式invokeSync、invokeAsync、invokeOneway等    private RemotingServer remotingServer;//Broker事件监听器，属于netty概念，监听chanel 4个动作事件，提供处理方法    private BrokerHousekeepingService brokerHousekeepingService;//remotingServer的并发处理器，处理各种类型请求    private ExecutorService remotingExecutor;//公告类，这里是namesrv和nettyserver2个配置文件，ReadWriteLock保证读写，对外提供获取及持久化，DataVersion（时间戳+AtomicLong counter自增）做版本控制，Properties对象做update、string-file中间对象。    private Configuration configuration;

重点聊一下这个方法：

public boolean initialize() {//加载kvConfig.json至KVConfigManager的configTable，即持久化转移到内存        this.kvConfigManager.load();//将namesrv作为一个netty server启动        this.remotingServer = new NettyRemotingServer(this.nettyServerConfig, this.brokerHousekeepingService);//启动请求处理线程池        this.remotingExecutor =            Executors.newFixedThreadPool(nettyServerConfig.getServerWorkerThreads(), new ThreadFactoryImpl("RemotingExecutorThread_"));//注册默认DefaultRequestProcessor和remotingExecutor，等start启动即开始处理netty请求        this.registerProcessor();//每10s检查2分钟接受不到心跳的broker清除掉        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {            @Override            public void run() {                NamesrvController.this.routeInfoManager.scanNotActiveBroker();            }        }, 5, 10, TimeUnit.SECONDS);//每10分钟，打印namesrv全局配置信息        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {            @Override            public void run() {                NamesrvController.this.kvConfigManager.printAllPeriodically();            }        }, 1, 10, TimeUnit.MINUTES);        return true;    }

NamesrvController这个类，几乎把namesrv模块的所有类都关联进去了，本身这个模块类也就8个，所以说非常轻量级。再重点聊一下DefaultRequestProcessor这个类就完了。
DefaultRequestProcessor实现NettyRequestProcessor接口，实现processRequest（处理请求）和rejectRequest（拒绝请求）方法；rejectRequest直接返回false，没有理由拒绝。

@Override    public RemotingCommand processRequest(ChannelHandlerContext ctx, RemotingCommand request) throws RemotingCommandException {        if (log.isDebugEnabled()) {            log.debug("receive request, {} {} {}",                request.getCode(),                RemotingHelper.parseChannelRemoteAddr(ctx.channel()),                request);        }        switch (request.getCode()) {            case RequestCode.PUT_KV_CONFIG:                return this.putKVConfig(ctx, request);            case RequestCode.GET_KV_CONFIG:                return this.getKVConfig(ctx, request);            case RequestCode.DELETE_KV_CONFIG:                return this.deleteKVConfig(ctx, request);            case RequestCode.REGISTER_BROKER:                Version brokerVersion = MQVersion.value2Version(request.getVersion());                if (brokerVersion.ordinal() >= MQVersion.Version.V3_0_11.ordinal()) {                    return this.registerBrokerWithFilterServer(ctx, request);                } else {                    return this.registerBroker(ctx, request);                }            case RequestCode.UNREGISTER_BROKER:                return this.unregisterBroker(ctx, request);            case RequestCode.GET_ROUTEINTO_BY_TOPIC:                return this.getRouteInfoByTopic(ctx, request);            case RequestCode.GET_BROKER_CLUSTER_INFO:                return this.getBrokerClusterInfo(ctx, request);            case RequestCode.WIPE_WRITE_PERM_OF_BROKER:                return this.wipeWritePermOfBroker(ctx, request);            case RequestCode.GET_ALL_TOPIC_LIST_FROM_NAMESERVER:                return getAllTopicListFromNameserver(ctx, request);            case RequestCode.DELETE_TOPIC_IN_NAMESRV:                return deleteTopicInNamesrv(ctx, request);            case RequestCode.GET_KVLIST_BY_NAMESPACE:                return this.getKVListByNamespace(ctx, request);            case RequestCode.GET_TOPICS_BY_CLUSTER:                return this.getTopicsByCluster(ctx, request);            case RequestCode.GET_SYSTEM_TOPIC_LIST_FROM_NS:                return this.getSystemTopicListFromNs(ctx, request);            case RequestCode.GET_UNIT_TOPIC_LIST:                return this.getUnitTopicList(ctx, request);            case RequestCode.GET_HAS_UNIT_SUB_TOPIC_LIST:                return this.getHasUnitSubTopicList(ctx, request);            case RequestCode.GET_HAS_UNIT_SUB_UNUNIT_TOPIC_LIST:                return this.getHasUnitSubUnUnitTopicList(ctx, request);            case RequestCode.UPDATE_NAMESRV_CONFIG:                return this.updateConfig(ctx, request);            case RequestCode.GET_NAMESRV_CONFIG:                return this.getConfig(ctx, request);            default:                break;        }        return null;

上面设计思想是把request和response封装在统一对象RemotingCommand里，通过REQUEST_COMMAND和RESPONSE_COMMAND来区分，RemotingCommand还有很多解析处理内容，包括反射解析CommandCustomHeader等。这里只是通过RequestCode解析出对应RemotingCommand，真正执行，在rocketmq-remoting模块，这个是典型的netty程序，可以参考
https://github.com/a2888409/RocketMQ-Learning/blob/master/book/ch2/2-remoting.md