# 聊聊 RocketMQ 的 Broker 源码 | Nicksxs's Blog
broker 的启动形式有点类似于 NameServer，都是服务类型的，跟 Consumer 差别比较大， 首先是org.apache.rocketmq.broker.BrokerStartup中的 main 函数，org.apache.rocketmq.broker.BrokerStartup#createBrokerController基本就是读取参数，这里差点把最核心的初始化给漏了， fi

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# 聊聊 RocketMQ 的 Broker 源码

发表于 2020-07-19 分类于 MQ ， RocketMQ ， 消息队列 ， RocketMQ ， 中间件 ， RocketMQ 阅读次数： 阅读次数： Disqus：

broker 的启动形式有点类似于 NameServer，都是服务类型的，跟 Consumer 差别比较大，

首先是org.apache.rocketmq.broker.BrokerStartup中的 main 函数，org.apache.rocketmq.broker.BrokerStartup#createBrokerController基本就是读取参数，这里差点把最核心的初始化给漏了，

    final BrokerController controller = new BrokerController(
                    brokerConfig,
                    nettyServerConfig,
                    nettyClientConfig,
                    messageStoreConfig);
                // remember all configs to prevent discard
                controller.getConfiguration().registerConfig(properties);

                boolean initResult = controller.initialize();

前面是以 broker 配置，netty 的服务端和客户端配置，以及消息存储配置在实例化 BrokerController，然后就是初始化了

    public boolean initialize() throws CloneNotSupportedException {
            boolean result = this.topicConfigManager.load();

            result = result && this.consumerOffsetManager.load();
            result = result && this.subscriptionGroupManager.load();
            result = result && this.consumerFilterManager.load();

前面这些就是各个配置的 load 了，然后是个我认为比较重要的部分messageStore 的实例化，

    if (result) {
        try {
            this.messageStore =
                new DefaultMessageStore(this.messageStoreConfig, this.brokerStatsManager, this.messageArrivingListener,
                    this.brokerConfig);
            if (messageStoreConfig.isEnableDLegerCommitLog()) {
                DLedgerRoleChangeHandler roleChangeHandler = new DLedgerRoleChangeHandler(this, (DefaultMessageStore) messageStore);
                ((DLedgerCommitLog)((DefaultMessageStore) messageStore).getCommitLog()).getdLedgerServer().getdLedgerLeaderElector().addRoleChangeHandler(roleChangeHandler);
            }
            this.brokerStats = new BrokerStats((DefaultMessageStore) this.messageStore);
            //load plugin
            MessageStorePluginContext context = new MessageStorePluginContext(messageStoreConfig, brokerStatsManager, messageArrivingListener, brokerConfig);
            this.messageStore = MessageStoreFactory.build(context, this.messageStore);
            this.messageStore.getDispatcherList().addFirst(new CommitLogDispatcherCalcBitMap(this.brokerConfig, this.consumerFilterManager));
        } catch (IOException e) {
            result = false;
            log.error("Failed to initialize", e);
        }
    }

    result = result && this.messageStore.load();

先是实例化，实例化构造函数里的代码比较重要，重点看一下

    public DefaultMessageStore(final MessageStoreConfig messageStoreConfig, final BrokerStatsManager brokerStatsManager,
            final MessageArrivingListener messageArrivingListener, final BrokerConfig brokerConfig) throws IOException {
            this.messageArrivingListener = messageArrivingListener;
            this.brokerConfig = brokerConfig;
            this.messageStoreConfig = messageStoreConfig;
            this.brokerStatsManager = brokerStatsManager;
            this.allocateMappedFileService = new AllocateMappedFileService(this);
            if (messageStoreConfig.isEnableDLegerCommitLog()) {
                this.commitLog = new DLedgerCommitLog(this);
            } else {
                this.commitLog = new CommitLog(this);
            }
            this.consumeQueueTable = new ConcurrentHashMap<>(32);

            this.flushConsumeQueueService = new FlushConsumeQueueService();
            this.cleanCommitLogService = new CleanCommitLogService();
            this.cleanConsumeQueueService = new CleanConsumeQueueService();
            this.storeStatsService = new StoreStatsService();
            this.indexService = new IndexService(this);
            if (!messageStoreConfig.isEnableDLegerCommitLog()) {
                this.haService = new HAService(this);
            } else {
                this.haService = null;
            }
            this.reputMessageService = new ReputMessageService();

            this.scheduleMessageService = new ScheduleMessageService(this);

            this.transientStorePool = new TransientStorePool(messageStoreConfig);

            if (messageStoreConfig.isTransientStorePoolEnable()) {
                this.transientStorePool.init();
            }

            this.allocateMappedFileService.start();

            this.indexService.start();

            this.dispatcherList = new LinkedList<>();
            this.dispatcherList.addLast(new CommitLogDispatcherBuildConsumeQueue());
            this.dispatcherList.addLast(new CommitLogDispatcherBuildIndex());

            File file = new File(StorePathConfigHelper.getLockFile(messageStoreConfig.getStorePathRootDir()));
            MappedFile.ensureDirOK(file.getParent());
            lockFile = new RandomAccessFile(file, "rw");
        }

这里面有很多类，不过先把从构造函数里传进来的忽略下，接下来就是 `AllocateMappedFileService` 这个service，前面看过文章的可能会根据上面的代码猜到，这也是个 ServiceThread，如果是对RocketMQ 有所了解的可能从名字可以看出这个类是关于 RocketMQ 消息怎么落盘的，当需要创建MappedFile时（在MapedFileQueue.getLastMapedFile方法中），向该线程的requestQueue队列中放入AllocateRequest请求对象，该线程会在后台监听该队列，并在后台创建MapedFile对象，即同时创建了物理文件。然后是创建了 IndexService 服务线程，用来给创建索引；还有是FlushConsumeQueueService是将ConsumeQueue 刷入磁盘；CleanCommitLogService用来清理过期的 CommitLog，默认是 72 小时以上；CleanConsumeQueueService是将小于最新的 CommitLog 偏移量的 ConsumeQueue 清理掉；StoreStatsService是储存统计服务；HAService用于CommitLog 的主备同步；ScheduleMessageService用于定时消息；还有就是这个ReputMessageService非常重要，就是由它实现了将 CommitLog 以 topic+queue 纬度构建 ConsumeQueue，后面TransientStorePool是异步刷盘时的存储buffer，也可以从后面的判断中看出来

    public boolean isTransientStorePoolEnable() {
            return transientStorePoolEnable && FlushDiskType.ASYNC_FLUSH == getFlushDiskType()
                && BrokerRole.SLAVE != getBrokerRole();
        }

再然后就是启动两个服务线程，dispatcherList是为CommitLog文件转发请求，差不多这个初始化就这些内容。

然后回到外层，下面是主备切换的配置，然后是数据统计，接着是存储插件加载，然后是往转发器链表里再加一个过滤器

    if (messageStoreConfig.isEnableDLegerCommitLog()) {
                DLedgerRoleChangeHandler roleChangeHandler = new DLedgerRoleChangeHandler(this, (DefaultMessageStore) messageStore);
                ((DLedgerCommitLog)((DefaultMessageStore) messageStore).getCommitLog()).getdLedgerServer().getdLedgerLeaderElector().addRoleChangeHandler(roleChangeHandler);
            }
            this.brokerStats = new BrokerStats((DefaultMessageStore) this.messageStore);
            //load plugin
            MessageStorePluginContext context = new MessageStorePluginContext(messageStoreConfig, brokerStatsManager, messageArrivingListener, brokerConfig);
            this.messageStore = MessageStoreFactory.build(context, this.messageStore);
            this.messageStore.getDispatcherList().addFirst(new CommitLogDispatcherCalcBitMap(this.brokerConfig, this.consumerFilterManager));

接下来就是org.apache.rocketmq.store.MessageStore#load的过程了，

1. 调用ScheduleMessageService.load方法，初始化延迟级别列表。将这些级别（”1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m 8m 9m 10m 20m 30m 1h 2h”）的延时存入延迟级别delayLevelTable：ConcurrentHashMap<Integer /* level */, Long/* delay timeMillis */>变量中，例如1s的kv值为1:1000,5s的kv值为2:5000，key值依次类推；每个延迟级别即为一个队列。

2)调用CommitLog.load方法，在此方法中调用MapedFileQueue.load方法，将$HOME /store/commitlog目录下的所有文件加载到MapedFileQueue的List<mapedfile>变量中；</mapedfile>

3)调用DefaultMessageStore.loadConsumeQueue方法加载consumequeue文件数据到DefaultMessageStore.consumeQueueTable集合中。

初始化StoreCheckPoint对象，加载$HOME/store/checkpoint文件，该文件记录三个字段值，分别是物理队列消息时间戳、逻辑队列消息时间戳、索引队列消息时间戳。

调用IndexService.load方法加载$HOME/store/index目录下的文件。对该目录下的每个文件初始化一个IndexFile对象。然后调用IndexFile对象的load方法将IndexHeader加载到对象的变量中；再根据检查是否存在abort文件，若有存在abort文件，则表示Broker表示上次是异常退出的，则检查checkpoint的indexMsgTimestamp字段值是否小于IndexHeader的endTimestamp值，indexMsgTimestamp值表示最后刷盘的时间，若小于则表示在最后刷盘之后在该文件中还创建了索引，则要删除该Index文件，否则将该IndexFile对象放入indexFileList:ArrayList<indexfile>索引文件集合中。</indexfile>

然后调用org.apache.rocketmq.store.DefaultMessageStore#recover恢复，前面有根据`boolean lastExitOK = !this.isTempFileExist();`临时文件是否存在来判断上一次是否正常退出，根据这个状态来选择什么恢复策略

接下去是初始化 Netty 服务端，初始化发送消息线程池（sendMessageExecutor）、拉取消息线程池（pullMessageExecutor）、管理Broker线程池（adminBrokerExecutor）、客户端管理线程池（clientManageExecutor），注册事件处理器，包括发送消息事件处理器（SendMessageProcessor）、拉取消息事件处理器、查询消息事件处理器（QueryMessageProcessor，包括客户端的心跳事件、注销事件、获取消费者列表事件、更新更新和查询消费进度consumerOffset）、客户端管理事件处理器（ClientManageProcessor）、结束事务处理器（EndTransactionProcessor）、默认事件处理器（AdminBrokerProcessor），然后是定时任务

`BrokerController.this.getBrokerStats().record();` 记录 Broker 状态

`BrokerController.this.consumerOffsetManager.persist();` 持久化consumerOffset

`BrokerController.this.consumerFilterManager.persist();`持久化consumerFilter

`BrokerController.this.protectBroker();` 保护 broker，消费慢，不让继续投递

`BrokerController.this.printWaterMark();` 打印水位

`log.info("dispatch behind commit log {} bytes", BrokerController.this.getMessageStore().dispatchBehindBytes());` 检查落后程度

`BrokerController.this.brokerOuterAPI.fetchNameServerAddr();` 定时获取 nameserver

`BrokerController.this.printMasterAndSlaveDiff();` 打印主从不一致

然后是 tsl，初始化事务消息，初始化 RPCHook

请把害怕打到公屏上🤦‍♂️，从线程池名字和调用的方法应该可以看出大部分的用途

    this.remotingServer = new NettyRemotingServer(this.nettyServerConfig, this.clientHousekeepingService);
                NettyServerConfig fastConfig = (NettyServerConfig) this.nettyServerConfig.clone();
                fastConfig.setListenPort(nettyServerConfig.getListenPort() - 2);
                this.fastRemotingServer = new NettyRemotingServer(fastConfig, this.clientHousekeepingService);
                this.sendMessageExecutor = new BrokerFixedThreadPoolExecutor(
                    this.brokerConfig.getSendMessageThreadPoolNums(),
                    this.brokerConfig.getSendMessageThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.sendThreadPoolQueue,
                    new ThreadFactoryImpl("SendMessageThread_"));

                this.pullMessageExecutor = new BrokerFixedThreadPoolExecutor(
                    this.brokerConfig.getPullMessageThreadPoolNums(),
                    this.brokerConfig.getPullMessageThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.pullThreadPoolQueue,
                    new ThreadFactoryImpl("PullMessageThread_"));

                this.replyMessageExecutor = new BrokerFixedThreadPoolExecutor(
                    this.brokerConfig.getProcessReplyMessageThreadPoolNums(),
                    this.brokerConfig.getProcessReplyMessageThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.replyThreadPoolQueue,
                    new ThreadFactoryImpl("ProcessReplyMessageThread_"));

                this.queryMessageExecutor = new BrokerFixedThreadPoolExecutor(
                    this.brokerConfig.getQueryMessageThreadPoolNums(),
                    this.brokerConfig.getQueryMessageThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.queryThreadPoolQueue,
                    new ThreadFactoryImpl("QueryMessageThread_"));

                this.adminBrokerExecutor =
                    Executors.newFixedThreadPool(this.brokerConfig.getAdminBrokerThreadPoolNums(), new ThreadFactoryImpl(
                        "AdminBrokerThread_"));

                this.clientManageExecutor = new ThreadPoolExecutor(
                    this.brokerConfig.getClientManageThreadPoolNums(),
                    this.brokerConfig.getClientManageThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.clientManagerThreadPoolQueue,
                    new ThreadFactoryImpl("ClientManageThread_"));

                this.heartbeatExecutor = new BrokerFixedThreadPoolExecutor(
                    this.brokerConfig.getHeartbeatThreadPoolNums(),
                    this.brokerConfig.getHeartbeatThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.heartbeatThreadPoolQueue,
                    new ThreadFactoryImpl("HeartbeatThread_", true));

                this.endTransactionExecutor = new BrokerFixedThreadPoolExecutor(
                    this.brokerConfig.getEndTransactionThreadPoolNums(),
                    this.brokerConfig.getEndTransactionThreadPoolNums(),
                    1000 * 60,
                    TimeUnit.MILLISECONDS,
                    this.endTransactionThreadPoolQueue,
                    new ThreadFactoryImpl("EndTransactionThread_"));

                this.consumerManageExecutor =
                    Executors.newFixedThreadPool(this.brokerConfig.getConsumerManageThreadPoolNums(), new ThreadFactoryImpl(
                        "ConsumerManageThread_"));

                this.registerProcessor();

                final long initialDelay = UtilAll.computeNextMorningTimeMillis() - System.currentTimeMillis();
                final long period = 1000 * 60 * 60 * 24;
                this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            BrokerController.this.getBrokerStats().record();
                        } catch (Throwable e) {
                            log.error("schedule record error.", e);
                        }
                    }
                }, initialDelay, period, TimeUnit.MILLISECONDS);

                this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            BrokerController.this.consumerOffsetManager.persist();
                        } catch (Throwable e) {
                            log.error("schedule persist consumerOffset error.", e);
                        }
                    }
                }, 1000 * 10, this.brokerConfig.getFlushConsumerOffsetInterval(), TimeUnit.MILLISECONDS);

                this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            BrokerController.this.consumerFilterManager.persist();
                        } catch (Throwable e) {
                            log.error("schedule persist consumer filter error.", e);
                        }
                    }
                }, 1000 * 10, 1000 * 10, TimeUnit.MILLISECONDS);

                this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            BrokerController.this.protectBroker();
                        } catch (Throwable e) {
                            log.error("protectBroker error.", e);
                        }
                    }
                }, 3, 3, TimeUnit.MINUTES);

                this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            BrokerController.this.printWaterMark();
                        } catch (Throwable e) {
                            log.error("printWaterMark error.", e);
                        }
                    }
                }, 10, 1, TimeUnit.SECONDS);

                this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

                    @Override
                    public void run() {
                        try {
                            log.info("dispatch behind commit log {} bytes", BrokerController.this.getMessageStore().dispatchBehindBytes());
                        } catch (Throwable e) {
                            log.error("schedule dispatchBehindBytes error.", e);
                        }
                    }
                }, 1000 * 10, 1000 * 60, TimeUnit.MILLISECONDS);

                if (this.brokerConfig.getNamesrvAddr() != null) {
                    this.brokerOuterAPI.updateNameServerAddressList(this.brokerConfig.getNamesrvAddr());
                    log.info("Set user specified name server address: {}", this.brokerConfig.getNamesrvAddr());
                } else if (this.brokerConfig.isFetchNamesrvAddrByAddressServer()) {
                    this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

                        @Override
                        public void run() {
                            try {
                                BrokerController.this.brokerOuterAPI.fetchNameServerAddr();
                            } catch (Throwable e) {
                                log.error("ScheduledTask fetchNameServerAddr exception", e);
                            }
                        }
                    }, 1000 * 10, 1000 * 60 * 2, TimeUnit.MILLISECONDS);
                }

                if (!messageStoreConfig.isEnableDLegerCommitLog()) {
                    if (BrokerRole.SLAVE == this.messageStoreConfig.getBrokerRole()) {
                        if (this.messageStoreConfig.getHaMasterAddress() != null && this.messageStoreConfig.getHaMasterAddress().length() >= 6) {
                            this.messageStore.updateHaMasterAddress(this.messageStoreConfig.getHaMasterAddress());
                            this.updateMasterHAServerAddrPeriodically = false;
                        } else {
                            this.updateMasterHAServerAddrPeriodically = true;
                        }
                    } else {
                        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
                            @Override
                            public void run() {
                                try {
                                    BrokerController.this.printMasterAndSlaveDiff();
                                } catch (Throwable e) {
                                    log.error("schedule printMasterAndSlaveDiff error.", e);
                                }
                            }
                        }, 1000 * 10, 1000 * 60, TimeUnit.MILLISECONDS);
                    }
                }

                if (TlsSystemConfig.tlsMode != TlsMode.DISABLED) {
                    // Register a listener to reload SslContext
                    try {
                        fileWatchService = new FileWatchService(
                            new String[] {
                                TlsSystemConfig.tlsServerCertPath,
                                TlsSystemConfig.tlsServerKeyPath,
                                TlsSystemConfig.tlsServerTrustCertPath
                            },
                            new FileWatchService.Listener() {
                                boolean certChanged, keyChanged = false;

                                @Override
                                public void onChanged(String path) {
                                    if (path.equals(TlsSystemConfig.tlsServerTrustCertPath)) {
                                        log.info("The trust certificate changed, reload the ssl context");
                                        reloadServerSslContext();
                                    }
                                    if (path.equals(TlsSystemConfig.tlsServerCertPath)) {
                                        certChanged = true;
                                    }
                                    if (path.equals(TlsSystemConfig.tlsServerKeyPath)) {
                                        keyChanged = true;
                                    }
                                    if (certChanged && keyChanged) {
                                        log.info("The certificate and private key changed, reload the ssl context");
                                        certChanged = keyChanged = false;
                                        reloadServerSslContext();
                                    }
                                }

                                private void reloadServerSslContext() {
                                    ((NettyRemotingServer) remotingServer).loadSslContext();
                                    ((NettyRemotingServer) fastRemotingServer).loadSslContext();
                                }
                            });
                    } catch (Exception e) {
                        log.warn("FileWatchService created error, can't load the certificate dynamically");
                    }
                }
                initialTransaction();
                initialAcl();
                initialRpcHooks();
            }
            return result;

Broker 启动过程

贴代码

    public void start() throws Exception {
            if (this.messageStore != null) {
                this.messageStore.start();
            }

            if (this.remotingServer != null) {
                this.remotingServer.start();
            }

            if (this.fastRemotingServer != null) {
                this.fastRemotingServer.start();
            }

            if (this.fileWatchService != null) {
                this.fileWatchService.start();
            }

            if (this.brokerOuterAPI != null) {
                this.brokerOuterAPI.start();
            }

            if (this.pullRequestHoldService != null) {
                this.pullRequestHoldService.start();
            }

            if (this.clientHousekeepingService != null) {
                this.clientHousekeepingService.start();
            }

            if (this.filterServerManager != null) {
                this.filterServerManager.start();
            }

            if (!messageStoreConfig.isEnableDLegerCommitLog()) {
                startProcessorByHa(messageStoreConfig.getBrokerRole());
                handleSlaveSynchronize(messageStoreConfig.getBrokerRole());
                this.registerBrokerAll(true, false, true);
            }

            this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

                @Override
                public void run() {
                    try {
                        BrokerController.this.registerBrokerAll(true, false, brokerConfig.isForceRegister());
                    } catch (Throwable e) {
                        log.error("registerBrokerAll Exception", e);
                    }
                }
            }, 1000 * 10, Math.max(10000, Math.min(brokerConfig.getRegisterNameServerPeriod(), 60000)), TimeUnit.MILLISECONDS);

            if (this.brokerStatsManager != null) {
                this.brokerStatsManager.start();
            }

            if (this.brokerFastFailure != null) {
                this.brokerFastFailure.start();
            }

        }

首先是启动messageStore，调用 start 方法，这里面又调用了一些代码

    public void start() throws Exception {

            lock = lockFile.getChannel().tryLock(0, 1, false);
            if (lock == null || lock.isShared() || !lock.isValid()) {
                throw new RuntimeException("Lock failed,MQ already started");
            }

            lockFile.getChannel().write(ByteBuffer.wrap("lock".getBytes()));
            lockFile.getChannel().force(true);
            {
                /**
                 * 1. Make sure the fast-forward messages to be truncated during the recovering according to the max physical offset of the commitlog;
                 * 2. DLedger committedPos may be missing, so the maxPhysicalPosInLogicQueue maybe bigger that maxOffset returned by DLedgerCommitLog, just let it go;
                 * 3. Calculate the reput offset according to the consume queue;
                 * 4. Make sure the fall-behind messages to be dispatched before starting the commitlog, especially when the broker role are automatically changed.
                 */
                long maxPhysicalPosInLogicQueue = commitLog.getMinOffset();
                for (ConcurrentMap<Integer, ConsumeQueue> maps : this.consumeQueueTable.values()) {
                    for (ConsumeQueue logic : maps.values()) {
                        if (logic.getMaxPhysicOffset() > maxPhysicalPosInLogicQueue) {
                            maxPhysicalPosInLogicQueue = logic.getMaxPhysicOffset();
                        }
                    }
                }
                if (maxPhysicalPosInLogicQueue < 0) {
                    maxPhysicalPosInLogicQueue = 0;
                }
                if (maxPhysicalPosInLogicQueue < this.commitLog.getMinOffset()) {
                    maxPhysicalPosInLogicQueue = this.commitLog.getMinOffset();
                    /**
                     * This happens in following conditions:
                     * 1. If someone removes all the consumequeue files or the disk get damaged.
                     * 2. Launch a new broker, and copy the commitlog from other brokers.
                     *
                     * All the conditions has the same in common that the maxPhysicalPosInLogicQueue should be 0.
                     * If the maxPhysicalPosInLogicQueue is gt 0, there maybe something wrong.
                     */
                    log.warn("[TooSmallCqOffset] maxPhysicalPosInLogicQueue={} clMinOffset={}", maxPhysicalPosInLogicQueue, this.commitLog.getMinOffset());
                }
                log.info("[SetReputOffset] maxPhysicalPosInLogicQueue={} clMinOffset={} clMaxOffset={} clConfirmedOffset={}",
                    maxPhysicalPosInLogicQueue, this.commitLog.getMinOffset(), this.commitLog.getMaxOffset(), this.commitLog.getConfirmOffset());
                this.reputMessageService.setReputFromOffset(maxPhysicalPosInLogicQueue);
                this.reputMessageService.start();

                /**
                 *  1. Finish dispatching the messages fall behind, then to start other services.
                 *  2. DLedger committedPos may be missing, so here just require dispatchBehindBytes <= 0
                 */
                while (true) {
                    if (dispatchBehindBytes() <= 0) {
                        break;
                    }
                    Thread.sleep(1000);
                    log.info("Try to finish doing reput the messages fall behind during the starting, reputOffset={} maxOffset={} behind={}", this.reputMessageService.getReputFromOffset(), this.getMaxPhyOffset(), this.dispatchBehindBytes());
                }
                this.recoverTopicQueueTable();
            }

            if (!messageStoreConfig.isEnableDLegerCommitLog()) {
                this.haService.start();
                this.handleScheduleMessageService(messageStoreConfig.getBrokerRole());
            }

            this.flushConsumeQueueService.start();
            this.commitLog.start();
            this.storeStatsService.start();

            this.createTempFile();
            this.addScheduleTask();
            this.shutdown = false;
        }

调用DefaultMessageStore.start方法启动DefaultMessageStore对象中的一些服务线程。

1. 启动ReputMessageService服务线程
2. 启动FlushConsumeQueueService服务线程；
3. 调用CommitLog.start方法，启动CommitLog对象中的FlushCommitLogService线程服务，若是同步刷盘（SYNC_FLUSH）则是启动GroupCommitService线程服务；若是异步刷盘（ASYNC_FLUSH）则是启动FlushRealTimeService线程服务；
4. 启动StoreStatsService线程服务；
5. 启动定时清理任务

然后是启动ClientHousekeepingService的 netty 服务端和客户端，然后是启动fileWatchService证书服务，接着启动BrokerOuterAPI中的NettyRemotingClient，即建立与NameServer的链接，用于自身Broker与其他模块的RPC功能调用；包括获取NameServer的地址、注册Broker、注销Broker、获取Topic配置、获取消息进度信息、获取订阅关系等RPC功能，然后是PullRequestHoldService服务线程，这个就是实现长轮询的，然后启动管家ClientHousekeepingService服务，负责扫描不活跃的生产者，消费者和 filter，启动FilterServerManager 过滤器服务管理，然后启动定时任务调用org.apache.rocketmq.broker.BrokerController#registerBrokerAll向所有 nameserver 注册 broker，最后是按需开启org.apache.rocketmq.store.stats.BrokerStatsManager和org.apache.rocketmq.broker.latency.BrokerFastFailure，基本上启动过程就完成了

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