RocketMQ源码解析四（Broker接收以及存储消息）

本是古典何须时尚 2022-09-12 07:46 275阅读 0赞

> **RocketMQ版本4.6.0，记录自己看源码的过程**

接收请求的入口已经在上篇分析过了，所以这里直接看处理器如何处理请求。

## 消息接收 ##

处理发送消息请求的处理器是SendMessageProcessor。

public class SendMessageProcessor extends AbstractSendMessageProcessor implements NettyRequestProcessor { 
    
        /** * 处理发送消息请求 */
        @Override
        public RemotingCommand processRequest(ChannelHandlerContext ctx,
                                              RemotingCommand request) throws RemotingCommandException { 
            SendMessageContext mqtraceContext;
            switch (request.getCode()) { 
                // 消费者发送的重试消息
                case RequestCode.CONSUMER_SEND_MSG_BACK:
                    return this.consumerSendMsgBack(ctx, request);
                // 生产者发送的普通消息
                default:
                    SendMessageRequestHeader requestHeader = parseRequestHeader(request);
                    if (requestHeader == null) { 
                        return null;
                    }
    
                    mqtraceContext = buildMsgContext(ctx, requestHeader);
                    this.executeSendMessageHookBefore(ctx, request, mqtraceContext);
    
                    RemotingCommand response;
                    if (requestHeader.isBatch()) { 
                        // 处理批量消息
                        response = this.sendBatchMessage(ctx, request, mqtraceContext, requestHeader);
                    } else { 
                        // 处理发送消息请求
                        response = this.sendMessage(ctx, request, mqtraceContext, requestHeader);
                    }
    
                    this.executeSendMessageHookAfter(response, mqtraceContext);
                    return response;
            }
        }
    }

这里只看处理单条消息的

/** * 处理发送消息请求 */
    private RemotingCommand sendMessage(final ChannelHandlerContext ctx,
                                        final RemotingCommand request,
                                        final SendMessageContext sendMessageContext,
                                        final SendMessageRequestHeader requestHeader) throws RemotingCommandException { 
    
        // 初始化响应
        final RemotingCommand response = RemotingCommand.createResponseCommand(SendMessageResponseHeader.class);
        final SendMessageResponseHeader responseHeader = (SendMessageResponseHeader)response.readCustomHeader();
    
        response.setOpaque(request.getOpaque());
    
        response.addExtField(MessageConst.PROPERTY_MSG_REGION, this.brokerController.getBrokerConfig().getRegionId());
        response.addExtField(MessageConst.PROPERTY_TRACE_SWITCH, String.valueOf(this.brokerController.getBrokerConfig().isTraceOn()));
    
        log.debug("receive SendMessage request command, {}", request);
    
        final long startTimstamp = this.brokerController.getBrokerConfig().getStartAcceptSendRequestTimeStamp();
        if (this.brokerController.getMessageStore().now() < startTimstamp) { 
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark(String.format("broker unable to service, until %s", UtilAll.timeMillisToHumanString2(startTimstamp)));
            return response;
        }
    
        response.setCode(-1);
        // 检查消息发送是否合理
        super.msgCheck(ctx, requestHeader, response);
        if (response.getCode() != -1) { 
            return response;
        }
    
        final byte[] body = request.getBody();
    
        // 要发送到的队列id
        int queueIdInt = requestHeader.getQueueId();
        // 要发送到的topic配置
        TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
    
        if (queueIdInt < 0) { 
            queueIdInt = Math.abs(this.random.nextInt() % 99999999) % topicConfig.getWriteQueueNums();
        }
    
        // 创建消息类
        MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
        msgInner.setTopic(requestHeader.getTopic());
        msgInner.setQueueId(queueIdInt);
    
        // 处理重试和死信
        // todo 不懂为什么这里会处理，因为重试不是在consumerSendMsgBack()这个方法里处理吗？
        if (!handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig)) { 
            return response;
        }
    
        msgInner.setBody(body);
        msgInner.setFlag(requestHeader.getFlag());
        MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties()));
        msgInner.setBornTimestamp(requestHeader.getBornTimestamp());
        msgInner.setBornHost(ctx.channel().remoteAddress());
        msgInner.setStoreHost(this.getStoreHost());
        msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes());
        String clusterName = this.brokerController.getBrokerConfig().getBrokerClusterName();
        MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_CLUSTER, clusterName);
        msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgInner.getProperties()));
        PutMessageResult putMessageResult = null;
        Map<String, String> oriProps = MessageDecoder.string2messageProperties(requestHeader.getProperties());
        String traFlag = oriProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED);
        // 校验是否不允许发送事务消息
        if (traFlag != null && Boolean.parseBoolean(traFlag)) { 
            if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) { 
                response.setCode(ResponseCode.NO_PERMISSION);
                response.setRemark(
                    "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()
                        + "] sending transaction message is forbidden");
                return response;
            }
            putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);
        } else { 
            // 使用MessageStore组件将消息存储在本地文件，只存储CommitLog文件，
            // ConsumerQueue文件和IndexFile文件会由后台线程异步存储
            putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
        }
    
        // 处理消息存储结果
        return handlePutMessageResult(putMessageResult, response, request, msgInner, responseHeader, sendMessageContext, ctx, queueIdInt);
    
    }

Step1：初始化响应数据；  
Step2：检查消息发送是否合理；  
Step3：获取要发送的队列和topic配置，如果queueId<0，则随机选择一个；  
Step4：构建消息类；  
Step5：处理重试和死信，对RETRY类型的消息处理。如果超过最大消费次数，则topic修改成"%DLQ%" + 分组名，即加入死信队列；  
Step6：如果是事务消息，则需要校验是否不允许发送事务消息；  
Step7：使用MessageStore组件将消息存储在本地文件，只存储CommitLog文件，ConsumerQueue文件和IndexFile文件会由后台线程异步存储；  
Step8：处理消息存储结果。

## 消息存储 ##

### 存储结构 ###

看源码之前，先看下存储结构  
**以下内容来源于「芋道源码」对RocketMQ源码的分析：**

`CommitLog`、`MappedFileQueue`、`MappedFile` 的关系如下：  
`CommitLog` : `MappedFileQueue` : `MappedFile` = 1 : 1 : N。

反应到系统文件如下：  
![在这里插入图片描述][130daa3fa0a1e6339e4df3db7afc8dfa.png_pic_center]  
`CommitLog`、`MappedFileQueue`、`MappedFile` 的定义如下：  
 ● `MappedFile` ：00000000000000000000、00000000001073741824、00000000002147483648等文件。  
 ● `MappedFileQueue` ：`MappedFile` 所在的文件夹，对 `MappedFile` 进行封装成文件队列，对上层提供可无限使用的文件容量。  
  ○ 每个 `MappedFile` 统一文件大小。  
  ○ 文件命名方式：fileName\[n\] = fileName\[n - 1\] + mappedFileSize。在 CommitLog 里默认为 1GB。  
 ● `CommitLog` ：针对 `MappedFileQueue` 的封装使用。  
`CommitLog` 目前存储在 `MappedFile` 有两种内容类型：  
 1.MESSAGE ：消息。  
 2. BLANK ：文件不足以存储消息时的空白占位。  
`CommitLog` 存储在 `MappedFile` 的结构：

![在这里插入图片描述][e1a04fb8ffb082968174196b7d68c00b.png_pic_center]  
`MESSAGE` 在 `CommitLog` 存储结构：

<table> 
 <thead> 
  <tr> 
   <th>第几位</th> 
   <th>字段</th> 
   <th>说明</th> 
   <th>数据类型</th> 
   <th>字节数</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>MsgLen</td> 
   <td>消息总长度</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>MagicCode</td> 
   <td>MESSAGE_MAGIC_CODE</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>BodyCRC</td> 
   <td>消息内容CRC</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>4</td> 
   <td>QueueId</td> 
   <td>消息队列编号</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>5</td> 
   <td>Flag</td> 
   <td>flag</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>6</td> 
   <td>QueueOffset</td> 
   <td>消息队列位置</td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>7</td> 
   <td>PhysicalOffset</td> 
   <td>物理位置。在 CommitLog 的顺序存储位置</td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>8</td> 
   <td>SysFlag</td> 
   <td>MessageSysFlag</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>9</td> 
   <td>BornTimestamp</td> 
   <td>生成消息时间戳</td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>10</td> 
   <td>BornHost</td> 
   <td>生效消息的地址+端口</td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>11</td> 
   <td>StoreTimestamp</td> 
   <td>存储消息时间戳</td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>12</td> 
   <td>StoreHost</td> 
   <td>存储消息的地址+端口</td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>13</td> 
   <td>ReconsumeTimes</td> 
   <td>重新消费消息次数</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>14</td> 
   <td>PreparedTransationOffset</td> 
   <td></td> 
   <td>Long</td> 
   <td>8</td> 
  </tr> 
  <tr> 
   <td>15</td> 
   <td>BodyLength + Body</td> 
   <td>内容长度 + 内容</td> 
   <td>Int + Bytes</td> 
   <td>4 + bodyLength</td> 
  </tr> 
  <tr> 
   <td>16</td> 
   <td>TopicLength + Topic</td> 
   <td>Topic长度 + Topic</td> 
   <td>Byte + Bytes</td> 
   <td>1 + topicLength</td> 
  </tr> 
  <tr> 
   <td>17</td> 
   <td>PropertiesLength + Properties</td> 
   <td>拓展字段长度 + 拓展字段</td> 
   <td>Short + Bytes</td> 
   <td>2 + PropertiesLength</td> 
  </tr> 
 </tbody> 
</table>

BLANK 在 `CommitLog` 存储结构：

<table> 
 <thead> 
  <tr> 
   <th>第几位</th> 
   <th>字段</th> 
   <th>说明</th> 
   <th>数据类型</th> 
   <th>字节数</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>maxBlank</td> 
   <td>空白长度</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>MagicCode</td> 
   <td>BLANK_MAGIC_CODE</td> 
   <td>Int</td> 
   <td>4</td> 
  </tr> 
 </tbody> 
</table>

### CommitLog存储流程 ###

消息存储是通过MessageStore组件来实现的  
**DefaultMessageStore**

public PutMessageResult putMessage(MessageExtBrokerInner msg) { 
        // 下面都是几种消息拒绝写入文件的情况
        if (this.shutdown) { 
            log.warn("message store has shutdown, so putMessage is forbidden");
            return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
        }
    
        if (BrokerRole.SLAVE == this.messageStoreConfig.getBrokerRole()) { 
            long value = this.printTimes.getAndIncrement();
            if ((value % 50000) == 0) { 
                log.warn("message store is slave mode, so putMessage is forbidden ");
            }
    
            return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
        }
    
        if (!this.runningFlags.isWriteable()) { 
            long value = this.printTimes.getAndIncrement();
            if ((value % 50000) == 0) { 
                log.warn("message store is not writeable, so putMessage is forbidden " + this.runningFlags.getFlagBits());
            }
    
            return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
        } else { 
            this.printTimes.set(0);
        }
    
        if (msg.getTopic().length() > Byte.MAX_VALUE) { 
            log.warn("putMessage message topic length too long " + msg.getTopic().length());
            return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, null);
        }
    
        if (msg.getPropertiesString() != null && msg.getPropertiesString().length() > Short.MAX_VALUE) { 
            log.warn("putMessage message properties length too long " + msg.getPropertiesString().length());
            return new PutMessageResult(PutMessageStatus.PROPERTIES_SIZE_EXCEEDED, null);
        }
    
        if (this.isOSPageCacheBusy()) { 
            return new PutMessageResult(PutMessageStatus.OS_PAGECACHE_BUSY, null);
        }
    
        long beginTime = this.getSystemClock().now();
        // 将消息存储到commitLog文件中
        PutMessageResult result = this.commitLog.putMessage(msg);
    
        long elapsedTime = this.getSystemClock().now() - beginTime;
        if (elapsedTime > 500) { 
            log.warn("putMessage not in lock elapsed time(ms)={}, bodyLength={}", elapsedTime, msg.getBody().length);
        }
        this.storeStatsService.setPutMessageEntireTimeMax(elapsedTime);
    
        if (null == result || !result.isOk()) { 
            this.storeStatsService.getPutMessageFailedTimes().incrementAndGet();
        }
    
        return result;
    }

使用commitLog存储消息：

public PutMessageResult putMessage(final MessageExtBrokerInner msg) { 
        // Set the storage time
        msg.setStoreTimestamp(System.currentTimeMillis());
        // Set the message body BODY CRC (consider the most appropriate setting
        // on the client)
        msg.setBodyCRC(UtilAll.crc32(msg.getBody()));
        // Back to Results
        AppendMessageResult result = null;
    
        StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService();
    
        String topic = msg.getTopic();
        int queueId = msg.getQueueId();
    
        final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag());
        if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE
            || tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) { 
            // 延时消息，则改变主题
            if (msg.getDelayTimeLevel() > 0) { 
                // 超过最大延时级别则设为最大延时级别
                if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) { 
                    msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel());
                }
    
                // topic设为SCHEDULE_TOPIC_XXXX
                topic = ScheduleMessageService.SCHEDULE_TOPIC;
                // 队列id = 延时级别-1
                queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel());
    
                // 备份真实主题和队列id，REAL_TOPIC为延时之前的topic，REAL_QID为延时之前的queueId
                MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic());
                MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId()));
                msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties()));
                // 延迟消息则需要将消息发送到延时主题上
                msg.setTopic(topic);
                msg.setQueueId(queueId);
            }
        }
    
        InetSocketAddress bornSocketAddress = (InetSocketAddress) msg.getBornHost();
        if (bornSocketAddress.getAddress() instanceof Inet6Address) { 
            msg.setBornHostV6Flag();
        }
    
        InetSocketAddress storeSocketAddress = (InetSocketAddress) msg.getStoreHost();
        if (storeSocketAddress.getAddress() instanceof Inet6Address) { 
            msg.setStoreHostAddressV6Flag();
        }
    
        long eclipsedTimeInLock = 0;
    
        MappedFile unlockMappedFile = null;
        // 获得最新的CommitLog文件
        MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();
    
        // 存储之前先获得锁，写文件肯定得一个个来，不能乱来
        putMessageLock.lock(); //spin or ReentrantLock ,depending on store config
        try { 
            long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now();
            this.beginTimeInLock = beginLockTimestamp;
    
            // Here settings are stored timestamp, in order to ensure an orderly
            // global
            msg.setStoreTimestamp(beginLockTimestamp);
    
            // 如果mappedFile为空，表明${ROCKETMQ_HOME}/store/commitlog目录下不存在任何文件，
            // 本次是该broker第一次消息发送，需要先创建一个偏移量为0的文件
            if (null == mappedFile || mappedFile.isFull()) { 
                mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise
            }
            if (null == mappedFile) { 
                log.error("create mapped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
                beginTimeInLock = 0;
                return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null);
            }
    
            // 将消息写入MappedFile映射的一块内存，根据刷盘策略择机刷盘，写入commitLog
            result = mappedFile.appendMessage(msg, this.appendMessageCallback);
            switch (result.getStatus()) { 
                // 消息追加到映射内存成功
                case PUT_OK:
                    break;
                // 文件不够大了，需要重新创建一个文件，再追加消息
                case END_OF_FILE:
                    unlockMappedFile = mappedFile;
                    // Create a new file, re-write the message
                    mappedFile = this.mappedFileQueue.getLastMappedFile(0);
                    if (null == mappedFile) { 
                        // XXX: warn and notify me
                        log.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
                        beginTimeInLock = 0;
                        return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result);
                    }
                    result = mappedFile.appendMessage(msg, this.appendMessageCallback);
                    break;
                // 消息长度超过最大允许长度
                case MESSAGE_SIZE_EXCEEDED:
                // 消息属性超过最大允许长度
                case PROPERTIES_SIZE_EXCEEDED:
                    beginTimeInLock = 0;
                    return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, result);
                case UNKNOWN_ERROR:
                    beginTimeInLock = 0;
                    return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
                default:
                    beginTimeInLock = 0;
                    return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
            }
    
            eclipsedTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp;
            beginTimeInLock = 0;
        } finally { 
            putMessageLock.unlock();
        }
    
        if (eclipsedTimeInLock > 500) { 
            log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", eclipsedTimeInLock, msg.getBody().length, result);
        }
    
        if (null != unlockMappedFile && this.defaultMessageStore.getMessageStoreConfig().isWarmMapedFileEnable()) { 
            this.defaultMessageStore.unlockMappedFile(unlockMappedFile);
        }
    
        // 到这里说明消息追加到映射内存成功了
        PutMessageResult putMessageResult = new PutMessageResult(PutMessageStatus.PUT_OK, result);
    
        // Statistics
        storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet();
        storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes());
    
        // 处理刷盘
        handleDiskFlush(result, putMessageResult, msg);
        // 处理broker之间的主从同步
        handleHA(result, putMessageResult, msg);
    
        return putMessageResult;
    }

Step1：如果是延时消息，则需要将消息发送到延时主题上，由后台定时任务定时从延时队列中取出消息重新放到原本主题对应的队列里供消费者消费。具体的流程由后面发送延时消息具体分析。  
Step2：获得最新的CommitLog文件。  
Step3：存储之前先获得锁。  
Step4：将消息写入MappedFile映射的一块内存，根据刷盘策略择机刷盘，写入commitLog。  
Step5：处理追加结果。  
step6：释放锁。  
Step7：处理CommitLog文件刷盘。  
Step8：处理broker之间的主从同步。

#### 消息写入映射内存 ####

MappedFile的属性：

/** * 操作系统每页大小，默认4K */
    public static final int OS_PAGE_SIZE = 1024 * 4;
    /** * 当前文件写指针的位置，默认从0开始 */
    protected final AtomicInteger wrotePosition = new AtomicInteger(0);
    protected final AtomicInteger committedPosition = new AtomicInteger(0);
    /** * 刷盘的指针位置，该指针之前的数据已经刷到磁盘了 */
    private final AtomicInteger flushedPosition = new AtomicInteger(0);
    /** * 文件大小 */
    protected int fileSize;
    protected FileChannel fileChannel;
    
    /** * Message will put to here first, and then reput to FileChannel if writeBuffer is not null. * 如果writeBuffer不为null，则消息会先存储在buffer，然后再提交到MappedFile对应的内存映射文件Buffer */
    protected ByteBuffer writeBuffer = null;
    protected TransientStorePool transientStorePool = null;
    /** * 文件名 */
    private String fileName;
    /** * 文件的初始偏移量 */
    private long fileFromOffset;
    /** * 物理文件 */
    private File file;
    /** * 对应的内存映射 */
    private MappedByteBuffer mappedByteBuffer;
    /** * 文件最后一次内容写入时间 */
    private volatile long storeTimestamp = 0;
    /** * 是否是文件目录中的第一个文件 */
    private boolean firstCreateInQueue = false;

appendMessage

public AppendMessageResult appendMessage(final MessageExtBrokerInner msg, final AppendMessageCallback cb) { 
        return appendMessagesInner(msg, cb);
    }
    
    public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb) { 
        assert messageExt != null;
        assert cb != null;
    
        // 先获取MappedFile当前的写指针
        int currentPos = this.wrotePosition.get();
    
        if (currentPos < this.fileSize) { 
            // 通过slice方法开辟一个子缓冲区，与mappedByteBuffer共享的内存区域
            ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice();
            byteBuffer.position(currentPos);
            AppendMessageResult result;
            // 开始写入映射内存区域
            if (messageExt instanceof MessageExtBrokerInner) { 
                result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBrokerInner) messageExt);
            } else if (messageExt instanceof MessageExtBatch) { 
                result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBatch) messageExt);
            } else { 
                return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
            }
            this.wrotePosition.addAndGet(result.getWroteBytes());
            this.storeTimestamp = result.getStoreTimestamp();
            return result;
        }
        // 文件已经写满了
        log.error("MappedFile.appendMessage return null, wrotePosition: {} fileSize: {}", currentPos, this.fileSize);
        return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
    }

class DefaultAppendMessageCallback implements AppendMessageCallback { 
        // File at the end of the minimum fixed length empty
        private static final int END_FILE_MIN_BLANK_LENGTH = 4 + 4;
        private final ByteBuffer msgIdMemory;
        private final ByteBuffer msgIdV6Memory;
        // 存储消息的内容
        private final ByteBuffer msgStoreItemMemory;
        // 消息的最大长度
        private final int maxMessageSize;
    
        public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
            final MessageExtBrokerInner msgInner) { 
            // STORETIMESTAMP + STOREHOSTADDRESS + OFFSET <br>
    
            // 在commitLog中的物理位置
            long wroteOffset = fileFromOffset + byteBuffer.position();
    
            int sysflag = msgInner.getSysFlag();
    
            int bornHostLength = (sysflag & MessageSysFlag.BORNHOST_V6_FLAG) == 0 ? 4 + 4 : 16 + 4;
            int storeHostLength = (sysflag & MessageSysFlag.STOREHOSTADDRESS_V6_FLAG) == 0 ? 4 + 4 : 16 + 4;
            ByteBuffer bornHostHolder = ByteBuffer.allocate(bornHostLength);
            ByteBuffer storeHostHolder = ByteBuffer.allocate(storeHostLength);
    
            this.resetByteBuffer(storeHostHolder, storeHostLength);
            // 创建消息ID
            String msgId;
            if ((sysflag & MessageSysFlag.STOREHOSTADDRESS_V6_FLAG) == 0) { 
                msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(storeHostHolder), wroteOffset);
            } else { 
                msgId = MessageDecoder.createMessageId(this.msgIdV6Memory, msgInner.getStoreHostBytes(storeHostHolder), wroteOffset);
            }
    
            // Record ConsumeQueue information
            keyBuilder.setLength(0);
            keyBuilder.append(msgInner.getTopic());
            keyBuilder.append('-');
            keyBuilder.append(msgInner.getQueueId());
            String key = keyBuilder.toString();
            Long queueOffset = CommitLog.this.topicQueueTable.get(key);
            if (null == queueOffset) { 
                queueOffset = 0L;
                CommitLog.this.topicQueueTable.put(key, queueOffset);
            }
    
            // Transaction messages that require special handling
            final int tranType = MessageSysFlag.getTransactionValue(msgInner.getSysFlag());
            switch (tranType) { 
                // Prepared and Rollback message is not consumed, will not enter the
                // consumer queuec
                case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
                case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
                    queueOffset = 0L;
                    break;
                case MessageSysFlag.TRANSACTION_NOT_TYPE:
                case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
                default:
                    break;
            }
    
            /** * Serialize message */
            final byte[] propertiesData =
                msgInner.getPropertiesString() == null ? null : msgInner.getPropertiesString().getBytes(MessageDecoder.CHARSET_UTF8);
    
            final int propertiesLength = propertiesData == null ? 0 : propertiesData.length;
    
            if (propertiesLength > Short.MAX_VALUE) { 
                log.warn("putMessage message properties length too long. length={}", propertiesData.length);
                return new AppendMessageResult(AppendMessageStatus.PROPERTIES_SIZE_EXCEEDED);
            }
    
            final byte[] topicData = msgInner.getTopic().getBytes(MessageDecoder.CHARSET_UTF8);
            final int topicLength = topicData.length;
    
            final int bodyLength = msgInner.getBody() == null ? 0 : msgInner.getBody().length;
    
            // 计算要存的总消息长度
            final int msgLen = calMsgLength(msgInner.getSysFlag(), bodyLength, topicLength, propertiesLength);
    
            // Exceeds the maximum message
            if (msgLen > this.maxMessageSize) { 
                CommitLog.log.warn("message size exceeded, msg total size: " + msgLen + ", msg body size: " + bodyLength
                    + ", maxMessageSize: " + this.maxMessageSize);
                return new AppendMessageResult(AppendMessageStatus.MESSAGE_SIZE_EXCEEDED);
            }
    
            // 文件没有多余的空间了，需要重新创建一个新的文件来存，剩余的空间写入BLANK占位
            if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) { 
                this.resetByteBuffer(this.msgStoreItemMemory, maxBlank);
                // 1 TOTALSIZE
                this.msgStoreItemMemory.putInt(maxBlank);
                // 2 MAGICCODE
                this.msgStoreItemMemory.putInt(CommitLog.BLANK_MAGIC_CODE);
                // 3 The remaining space may be any value
                // Here the length of the specially set maxBlank
                final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
                byteBuffer.put(this.msgStoreItemMemory.array(), 0, maxBlank);
                return new AppendMessageResult(AppendMessageStatus.END_OF_FILE, wroteOffset, maxBlank, msgId, msgInner.getStoreTimestamp(),
                    queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills);
            }
    
            // Initialization of storage space
            this.resetByteBuffer(msgStoreItemMemory, msgLen);
            // 将数据写入ByteBuffer
            // 1 TOTALSIZE
            this.msgStoreItemMemory.putInt(msgLen);
            // 2 MAGICCODE
            this.msgStoreItemMemory.putInt(CommitLog.MESSAGE_MAGIC_CODE);
            // 3 BODYCRC
            this.msgStoreItemMemory.putInt(msgInner.getBodyCRC());
            // 4 QUEUEID
            this.msgStoreItemMemory.putInt(msgInner.getQueueId());
            // 5 FLAG
            this.msgStoreItemMemory.putInt(msgInner.getFlag());
            // 6 QUEUEOFFSET
            this.msgStoreItemMemory.putLong(queueOffset);
            // 7 PHYSICALOFFSET
            this.msgStoreItemMemory.putLong(fileFromOffset + byteBuffer.position());
            // 8 SYSFLAG
            this.msgStoreItemMemory.putInt(msgInner.getSysFlag());
            // 9 BORNTIMESTAMP
            this.msgStoreItemMemory.putLong(msgInner.getBornTimestamp());
            // 10 BORNHOST
            this.resetByteBuffer(bornHostHolder, bornHostLength);
            this.msgStoreItemMemory.put(msgInner.getBornHostBytes(bornHostHolder));
            // 11 STORETIMESTAMP
            this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp());
            // 12 STOREHOSTADDRESS
            this.resetByteBuffer(storeHostHolder, storeHostLength);
            this.msgStoreItemMemory.put(msgInner.getStoreHostBytes(storeHostHolder));
            // 13 RECONSUMETIMES
            this.msgStoreItemMemory.putInt(msgInner.getReconsumeTimes());
            // 14 Prepared Transaction Offset
            this.msgStoreItemMemory.putLong(msgInner.getPreparedTransactionOffset());
            // 15 BODY
            this.msgStoreItemMemory.putInt(bodyLength);
            if (bodyLength > 0)
                this.msgStoreItemMemory.put(msgInner.getBody());
            // 16 TOPIC
            this.msgStoreItemMemory.put((byte) topicLength);
            this.msgStoreItemMemory.put(topicData);
            // 17 PROPERTIES
            this.msgStoreItemMemory.putShort((short) propertiesLength);
            if (propertiesLength > 0)
                this.msgStoreItemMemory.put(propertiesData);
    
            final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
            // 将消息写入byteBuffer，这里还只是在映射的内存中，后面需要根据刷盘策略持久化到磁盘中
            byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen);
    
            // 创建追加消息的结果
            AppendMessageResult result = new AppendMessageResult(AppendMessageStatus.PUT_OK, wroteOffset, msgLen, msgId,
                msgInner.getStoreTimestamp(), queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills);
    
            switch (tranType) { 
                case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
                case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
                    break;
                case MessageSysFlag.TRANSACTION_NOT_TYPE:
                case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
                    // The next update ConsumeQueue information
                    CommitLog.this.topicQueueTable.put(key, ++queueOffset);
                    break;
                default:
                    break;
            }
            return result;
        }
    }

这里只是将数据追加到内存中，需要根据是同步刷盘还是异步刷盘方式，将消息持久化到磁盘。

#### 处理commitLog刷盘 ####

在启动broker服务过程中，对BrokerController进行初始化时，会创建消息存储服务DefaultMessageStore。而在创建DefaultMessageStore的过程中，又会创建多个存储相关的服务，其中有个commitLog服务，接着在创建CommitLog中就会创建commitLog刷盘线程。

public CommitLog(final DefaultMessageStore defaultMessageStore) { 
        this.mappedFileQueue = new MappedFileQueue(defaultMessageStore.getMessageStoreConfig().getStorePathCommitLog(),
            defaultMessageStore.getMessageStoreConfig().getMappedFileSizeCommitLog(), defaultMessageStore.getAllocateMappedFileService());
        this.defaultMessageStore = defaultMessageStore;
    
        // 创建对CommitLog的刷盘服务
        if (FlushDiskType.SYNC_FLUSH == defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) { 
            // 同步刷盘
            this.flushCommitLogService = new GroupCommitService();
        } else { 
            // 异步刷盘
            this.flushCommitLogService = new FlushRealTimeService();
        }
    
        this.commitLogService = new CommitRealTimeService();
    
        this.appendMessageCallback = new DefaultAppendMessageCallback(defaultMessageStore.getMessageStoreConfig().getMaxMessageSize());
        batchEncoderThreadLocal = new ThreadLocal<MessageExtBatchEncoder>() { 
            @Override
            protected MessageExtBatchEncoder initialValue() { 
                return new MessageExtBatchEncoder(defaultMessageStore.getMessageStoreConfig().getMaxMessageSize());
            }
        };
        this.putMessageLock = defaultMessageStore.getMessageStoreConfig().isUseReentrantLockWhenPutMessage() ? new PutMessageReentrantLock() : new PutMessageSpinLock();
    
    }

而这些嵌套的服务又一个接着一个启动，最终在CommitLog中启动commitLog刷盘线程：

public void start() { 
        // 启动刷盘线程
        this.flushCommitLogService.start();
    
        if (defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) { 
            this.commitLogService.start();
        }
    }

所以在broker启动时，commitLog刷盘线程就已经启动了，通过不断循环的执行。  
其中，刷盘线程有3种

<table> 
 <thead> 
  <tr> 
   <th>线程服务</th> 
   <th>场景</th> 
   <th>插入消息性能</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>CommitRealTimeService</td> 
   <td>异步刷盘 &amp;&amp; 开启内存字节缓冲区</td> 
   <td>第一</td> 
  </tr> 
  <tr> 
   <td>CommitRealTimeService</td> 
   <td>异步刷盘 &amp;&amp; 关闭内存字节缓冲区</td> 
   <td>第二</td> 
  </tr> 
  <tr> 
   <td>GroupCommitService</td> 
   <td>同步刷盘</td> 
   <td>第三</td> 
  </tr> 
 </tbody> 
</table>

这里主要分析同步刷盘。  
接着上面消息写入映射内存后的处理刷盘

/** * 处理刷盘动作 */
    public void handleDiskFlush(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) { 
        // 同步刷盘
        if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) { 
            // 刷盘线程
            final GroupCommitService service = (GroupCommitService) this.flushCommitLogService;
            // 是否等待消息存储完成后在返回 todo 如果该值false，就相当于异步刷盘？？
            if (messageExt.isWaitStoreMsgOK()) { 
                // 创建一个刷盘request提交给刷盘线程去刷盘，其实最终就是调用MappedByteBuffer的force()方法强制将内存的数据刷到磁盘中
                GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
                // 将刷盘请求提交给GroupCommitService线程，线程会定时处理该request
                service.putRequest(request);
                // 等待刷盘完成
                boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
                if (!flushOK) { 
                    log.error("do groupcommit, wait for flush failed, topic: " + messageExt.getTopic() + " tags: " + messageExt.getTags()
                        + " client address: " + messageExt.getBornHostString());
                    // 刷盘超时
                    putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT);
                }
            } else { 
                service.wakeup();
            }
        }
        // 异步刷盘，根据是否开启TransientStorePoolEnable不同处理，
        // 1、false：默认，就直接唤醒刷盘线程后就返回了
        // 2、true：会单独申请一个与目标物理文件同样大小的堆外内存，该堆外内存将使用内存锁定，
        // 确保不会被置换到虚拟内存中去，消息首先追加到堆外内存，然后提交到与物理文件
        // 的内存映射内存中，再刷盘
        else { 
            if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) { 
                flushCommitLogService.wakeup();
            } else { 
                commitLogService.wakeup();
            }
        }
    }

由于刷盘线程启动后就一直在执行，那不可能每次循环都会有消息要刷盘，所以不能一直空循环，每次循环完都要阻塞或沉睡一段时间，等到时间或有刷盘请求进来了就唤醒来处理刷盘。  
所以当创建一个刷盘请求提交给刷盘线程时，如果线程刚好在沉睡状态，就会唤醒它

/** * 同步刷盘服务 */
    class GroupCommitService extends FlushCommitLogService { 
        /** * 同步刷盘任务暂存容器 */
        private volatile List<GroupCommitRequest> requestsWrite = new ArrayList<GroupCommitRequest>();
        /** * 用作避免任务提交和任务执行的锁冲突 */
        private volatile List<GroupCommitRequest> requestsRead = new ArrayList<GroupCommitRequest>();
    
        /** * 提交刷盘请求 */
        public synchronized void putRequest(final GroupCommitRequest request) { 
            synchronized (this.requestsWrite) { 
                this.requestsWrite.add(request);
            }
            // 任务提交时如果在沉睡就将其立即唤醒来执行刷盘
            if (hasNotified.compareAndSet(false, true)) { 
                waitPoint.countDown(); // notify
            }
        }
    
        /** * 每次刷盘完后，交换刷盘任务的写队列和读队列，然后写队列继续写，读队列继续读，不用产生锁竞争， * 等读队列中的请求执行完后，接着交换执行 * * 这里不会造成对ArrayList的并发读写吗？ * 不会，因为交换期间还在add，交换后write和read都是指向 * 同一个对象，所以这时读要获取的是写操作获得的锁，竞争的是同一把锁，读会阻塞，所以这个期间不会造成并发问题 */
        private void swapRequests() { 
            List<GroupCommitRequest> tmp = this.requestsWrite;
            this.requestsWrite = this.requestsRead;
            this.requestsRead = tmp;
        }
    
        private void doCommit() { 
            synchronized (this.requestsRead) { 
                if (!this.requestsRead.isEmpty()) { 
                    for (GroupCommitRequest req : this.requestsRead) { 
                        // There may be a message in the next file, so a maximum of
                        // two times the flush
                        boolean flushOK = false;
                        for (int i = 0; i < 2 && !flushOK; i++) { 
                            // 如果已刷盘点大于要提交的刷盘点，说明已刷盘成功
                            flushOK = CommitLog.this.mappedFileQueue.getFlushedWhere() >= req.getNextOffset();
    
                            if (!flushOK) { 
                                // 刷盘，最终调用mappedByteBuffer.force()强制刷盘
                                CommitLog.this.mappedFileQueue.flush(0);
                            }
                        }
                        // 刷盘完成，唤醒等待该任务结果的线程
                        req.wakeupCustomer(flushOK);
                    }
    
                    long storeTimestamp = CommitLog.this.mappedFileQueue.getStoreTimestamp();
                    if (storeTimestamp > 0) { 
                        // 记录刷盘时间点
                        CommitLog.this.defaultMessageStore.getStoreCheckpoint().setPhysicMsgTimestamp(storeTimestamp);
                    }
    
                    this.requestsRead.clear();
                } else { 
                    // Because of individual messages is set to not sync flush, it
                    // will come to this process
                    CommitLog.this.mappedFileQueue.flush(0);
                }
            }
        }
    
        /** * 该线程随着broker启动而启动 */
        public void run() { 
            CommitLog.log.info(this.getServiceName() + " service started");
    
            while (!this.isStopped()) { 
                try { 
                    // 间隔10ms执行一次，执行下次刷盘之前先交换下读写列表
                    // 正式阻塞之前会交换读写队列
                    this.waitForRunning(10);
                    this.doCommit();
                } catch (Exception e) { 
                    CommitLog.log.warn(this.getServiceName() + " service has exception. ", e);
                }
            }
    
            // Under normal circumstances shutdown, wait for the arrival of the
            // request, and then flush
            try { 
                Thread.sleep(10);
            } catch (InterruptedException e) { 
                CommitLog.log.warn("GroupCommitService Exception, ", e);
            }
    
            synchronized (this) { 
                this.swapRequests();
            }
    
            this.doCommit();
    
            CommitLog.log.info(this.getServiceName() + " service end");
        }
    
        @Override
        protected void onWaitEnd() { 
            this.swapRequests();
        }
    
        @Override
        public String getServiceName() { 
            return GroupCommitService.class.getSimpleName();
        }
    
        @Override
        public long getJointime() { 
            return 1000 * 60 * 5;
        }
    }

这里有一个设计点，每次刷盘完后，交换刷盘任务的写队列和读队列，然后写队列继续写，读队列继续读，不用产生锁竞争， 等读队列中的请求执行完后，接着交换执行。  
在阻塞等待之前会进行交换

protected void waitForRunning(long interval) { 
        if (hasNotified.compareAndSet(true, false)) { 
            // 最终调用GroupCommitService类的swapRequests方法，交换读写队列
            this.onWaitEnd();
            return;
        }
    
        // 重置计数器
        waitPoint.reset();
    
        try { 
            // 阻塞，等待被唤醒或超时唤醒
            waitPoint.await(interval, TimeUnit.MILLISECONDS);
        } catch (InterruptedException e) { 
            log.error("Interrupted", e);
        } finally { 
            hasNotified.set(false);
            this.onWaitEnd();
        }
    }

### ConsumerQueue和IndexFile存储流程 ###

在commitLog刷盘完成，消息已经写入磁盘后，后台会有一个线程，会间隔1ms循环不断将commitLog中新增的消息转发到ConsumerQueue和IndexFile文件中。

class ReputMessageService extends ServiceThread { 
    
        private volatile long reputFromOffset = 0;
    
        private void doReput() { 
            // 如果转发偏移量比commitLog的最小的偏移量还小，则重新设置为commitLog的最小的偏移量
            if (this.reputFromOffset < DefaultMessageStore.this.commitLog.getMinOffset()) { 
                log.warn("The reputFromOffset={} is smaller than minPyOffset={}, this usually indicate that the dispatch behind too much and the commitlog has expired.",
                    this.reputFromOffset, DefaultMessageStore.this.commitLog.getMinOffset());
                this.reputFromOffset = DefaultMessageStore.this.commitLog.getMinOffset();
            }
            for (boolean doNext = true; this.isCommitLogAvailable() && doNext; ) { 
    
                if (DefaultMessageStore.this.getMessageStoreConfig().isDuplicationEnable()
                    && this.reputFromOffset >= DefaultMessageStore.this.getConfirmOffset()) { 
                    break;
                }
    
                // 返回commitLog从reputFromOffset偏移量开始的消息
                SelectMappedBufferResult result = DefaultMessageStore.this.commitLog.getData(reputFromOffset);
                if (result != null) { 
                    try { 
                        this.reputFromOffset = result.getStartOffset();
    
                        // 遍历每条消息
                        for (int readSize = 0; readSize < result.getSize() && doNext; ) { 
                            // 从ByteBuffer中取出一条消息，封装成DispatchRequest对象
                            DispatchRequest dispatchRequest =
                                DefaultMessageStore.this.commitLog.checkMessageAndReturnSize(result.getByteBuffer(), false, false);
                            int size = dispatchRequest.getBufferSize() == -1 ? dispatchRequest.getMsgSize() : dispatchRequest.getBufferSize();
    
                            if (dispatchRequest.isSuccess()) { 
                                if (size > 0) { 
                                    // 消息转发给ConsumerQueue和IndexFile文件
                                    DefaultMessageStore.this.doDispatch(dispatchRequest);
    
                                    if (BrokerRole.SLAVE != DefaultMessageStore.this.getMessageStoreConfig().getBrokerRole()
                                        && DefaultMessageStore.this.brokerConfig.isLongPollingEnable()) { 
                                        DefaultMessageStore.this.messageArrivingListener.arriving(dispatchRequest.getTopic(),
                                            dispatchRequest.getQueueId(), dispatchRequest.getConsumeQueueOffset() + 1,
                                            dispatchRequest.getTagsCode(), dispatchRequest.getStoreTimestamp(),
                                            dispatchRequest.getBitMap(), dispatchRequest.getPropertiesMap());
                                    }
    
                                    this.reputFromOffset += size;
                                    readSize += size;
                                    if (DefaultMessageStore.this.getMessageStoreConfig().getBrokerRole() == BrokerRole.SLAVE) { 
                                        DefaultMessageStore.this.storeStatsService
                                            .getSinglePutMessageTopicTimesTotal(dispatchRequest.getTopic()).incrementAndGet();
                                        DefaultMessageStore.this.storeStatsService
                                            .getSinglePutMessageTopicSizeTotal(dispatchRequest.getTopic())
                                            .addAndGet(dispatchRequest.getMsgSize());
                                    }
                                } else if (size == 0) { 
                                    this.reputFromOffset = DefaultMessageStore.this.commitLog.rollNextFile(this.reputFromOffset);
                                    readSize = result.getSize();
                                }
                            } else if (!dispatchRequest.isSuccess()) { 
    
                                if (size > 0) { 
                                    log.error("[BUG]read total count not equals msg total size. reputFromOffset={}", reputFromOffset);
                                    this.reputFromOffset += size;
                                } else { 
                                    doNext = false;
                                    // If user open the dledger pattern or the broker is master node,
                                    // it will not ignore the exception and fix the reputFromOffset variable
                                    if (DefaultMessageStore.this.getMessageStoreConfig().isEnableDLegerCommitLog() ||
                                        DefaultMessageStore.this.brokerConfig.getBrokerId() == MixAll.MASTER_ID) { 
                                        log.error("[BUG]dispatch message to consume queue error, COMMITLOG OFFSET: {}",
                                            this.reputFromOffset);
                                        this.reputFromOffset += result.getSize() - readSize;
                                    }
                                }
                            }
                        }
                    } finally { 
                        result.release();
                    }
                } else { 
                    doNext = false;
                }
            }
        }
    
        @Override
        public void run() { 
            DefaultMessageStore.log.info(this.getServiceName() + " service started");
    
            while (!this.isStopped()) { 
                try { 
                    Thread.sleep(1);
                    this.doReput();
                } catch (Exception e) { 
                    DefaultMessageStore.log.warn(this.getServiceName() + " service has exception. ", e);
                }
            }
    
            DefaultMessageStore.log.info(this.getServiceName() + " service end");
        }
    }

从commitLog取出消息分别转发到ConsumerQueue和IndexFile  
**DefaultMessageStore**

public void doDispatch(DispatchRequest req) { 
        // 分别转发到ConsumerQueue和IndexFile
        for (CommitLogDispatcher dispatcher : this.dispatcherList) { 
            dispatcher.dispatch(req);
        }
    }

dispatcherList在DefaultMessageStore组件创建的时候就初始化添加了

/** * 消息转发列表，这里可以看出需要转发到ConsumerQueue和IndexFile这两个文件 */
    this.dispatcherList = new LinkedList<>();
    this.dispatcherList.addLast(new CommitLogDispatcherBuildConsumeQueue());
    this.dispatcherList.addLast(new CommitLogDispatcherBuildIndex());

#### 构建消息消费队列文件 ####

class CommitLogDispatcherBuildConsumeQueue implements CommitLogDispatcher { 
    
        @Override
        public void dispatch(DispatchRequest request) { 
            final int tranType = MessageSysFlag.getTransactionValue(request.getSysFlag());
            switch (tranType) { 
                case MessageSysFlag.TRANSACTION_NOT_TYPE:
                case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
                    DefaultMessageStore.this.putMessagePositionInfo(request);
                    break;
                case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
                case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
                    break;
            }
        }
    }

public void putMessagePositionInfo(DispatchRequest dispatchRequest) { 
        // 根据topic和queueId找到一个ConsumerQueue文件
        ConsumeQueue cq = this.findConsumeQueue(dispatchRequest.getTopic(), dispatchRequest.getQueueId());
        // 将消息存入ConsumerQueue
        cq.putMessagePositionInfoWrapper(dispatchRequest);
    }

这里存储也只是存到共享内存，由后台定时任务定时刷盘。

#### 构建消息索引文件 ####

class CommitLogDispatcherBuildIndex implements CommitLogDispatcher { 
    
        @Override
        public void dispatch(DispatchRequest request) { 
            if (DefaultMessageStore.this.messageStoreConfig.isMessageIndexEnable()) { 
                // 提交给index服务执行
                DefaultMessageStore.this.indexService.buildIndex(request);
            }
        }
    }

将请求提交给index服务执行  
**IndexService**

public void buildIndex(DispatchRequest req) { 
        // 获取或创建IndexFile文件
        IndexFile indexFile = retryGetAndCreateIndexFile();
        if (indexFile != null) { 
            long endPhyOffset = indexFile.getEndPhyOffset();
            DispatchRequest msg = req;
            String topic = msg.getTopic();
            String keys = msg.getKeys();
    
            // 如果该消息的偏移量小于indexFile文件中的偏移量，说明是重复消息，忽略该条消息
            if (msg.getCommitLogOffset() < endPhyOffset) { 
                return;
            }
    
            final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag());
            switch (tranType) { 
                case MessageSysFlag.TRANSACTION_NOT_TYPE:
                case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
                case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
                    break;
                case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
                    return;
            }
    
            if (req.getUniqKey() != null) { 
                indexFile = putKey(indexFile, msg, buildKey(topic, req.getUniqKey()));
                if (indexFile == null) { 
                    log.error("putKey error commitlog {} uniqkey {}", req.getCommitLogOffset(), req.getUniqKey());
                    return;
                }
            }
    
            if (keys != null && keys.length() > 0) { 
                String[] keyset = keys.split(MessageConst.KEY_SEPARATOR);
                for (int i = 0; i < keyset.length; i++) { 
                    String key = keyset[i];
                    if (key.length() > 0) { 
                        indexFile = putKey(indexFile, msg, buildKey(topic, key));
                        if (indexFile == null) { 
                            log.error("putKey error commitlog {} uniqkey {}", req.getCommitLogOffset(), req.getUniqKey());
                            return;
                        }
                    }
                }
            }
        } else { 
            log.error("build index error, stop building index");
        }
    }

这部分就到这吧。  
![在这里插入图片描述][93f21c82fc555f8aef668a6440239cb6.png_pic_center]  
![在这里插入图片描述][0a43d796ceb64730f52cb42f9ab67589.png_pic_center]

## 参考资料 ##

《儒猿技术窝——从 0 开始带你成为消息中间件实战高手》

[130daa3fa0a1e6339e4df3db7afc8dfa.png_pic_center]: /images/20220828/19c4ff3c70c04bb78d925381b65ac5bd.png
[e1a04fb8ffb082968174196b7d68c00b.png_pic_center]: /images/20220828/53475b98f27e42078e59fd69572eb58d.png
[93f21c82fc555f8aef668a6440239cb6.png_pic_center]: /images/20220828/91b87a7b2a9f4fc9b681765d18a06b1d.png
[0a43d796ceb64730f52cb42f9ab67589.png_pic_center]: /images/20220828/4133f4be77e64dbdb0971a4723abdcd3.png