RocketMQ中Broker的消息存储源码分析

Broker和前面分析过的NameServer类似，需要在Pipeline责任链上通过NettyServerHandler来处理消息

实际上就通过前面提到的SendMessageProcessor的processRequest方法处理

SendMessageProcessor的processRequest方法：

 1 public RemotingCommand processRequest(ChannelHandlerContext ctx,
 2                                           RemotingCommand request) throws RemotingCommandException {
 3     SendMessageContext mqtraceContext;
 4     switch (request.getCode()) {
 5         case RequestCode.CONSUMER_SEND_MSG_BACK:
 6             return this.consumerSendMsgBack(ctx, request);
 7         default:
 8             SendMessageRequestHeader requestHeader = parseRequestHeader(request);
 9             if (requestHeader == null) {
10                 return null;
11             }
12 
13             mqtraceContext = buildMsgContext(ctx, requestHeader);
14             this.executeSendMessageHookBefore(ctx, request, mqtraceContext);
15 
16             RemotingCommand response;
17             if (requestHeader.isBatch()) {
18                 response = this.sendBatchMessage(ctx, request, mqtraceContext, requestHeader);
19             } else {
20                 response = this.sendMessage(ctx, request, mqtraceContext, requestHeader);
21             }
22 
23             this.executeSendMessageHookAfter(response, mqtraceContext);
24             return response;
25     }
26 }

这里讨论Producer发送的消息，直接进入default语句

根据请求RemotingCommand，通过parseRequestHeader以及buildMsgContext方法，解析RemotingCommand中的相应信息，再封装到SendMessageRequestHeader和SendMessageContext中

接着调用executeSendMessageHookBefore方法：

 1 public void executeSendMessageHookBefore(final ChannelHandlerContext ctx, final RemotingCommand request,
 2    SendMessageContext context) {
 3     if (hasSendMessageHook()) {
 4         for (SendMessageHook hook : this.sendMessageHookList) {
 5             try {
 6                 final SendMessageRequestHeader requestHeader = parseRequestHeader(request);
 7 
 8                 if (null != requestHeader) {
 9                     context.setProducerGroup(requestHeader.getProducerGroup());
10                     context.setTopic(requestHeader.getTopic());
11                     context.setBodyLength(request.getBody().length);
12                     context.setMsgProps(requestHeader.getProperties());
13                     context.setBornHost(RemotingHelper.parseChannelRemoteAddr(ctx.channel()));
14                     context.setBrokerAddr(this.brokerController.getBrokerAddr());
15                     context.setQueueId(requestHeader.getQueueId());
16                 }
17 
18                 hook.sendMessageBefore(context);
19                 if (requestHeader != null) {
20                     requestHeader.setProperties(context.getMsgProps());
21                 }
22             } catch (Throwable e) {
23                 // Ignore
24             }
25         }
26     }
27 }

这里会执行所有SendMessageHook钩子的sendMessageBefore方法

然后调用sendMessage方法。进一步处理

sendMessage方法：

 1 private RemotingCommand sendMessage(final ChannelHandlerContext ctx,
 2                                     final RemotingCommand request,
 3                                     final SendMessageContext sendMessageContext,
 4                                     final SendMessageRequestHeader requestHeader) throws RemotingCommandException {
 5 
 6     final RemotingCommand response = RemotingCommand.createResponseCommand(SendMessageResponseHeader.class);
 7     final SendMessageResponseHeader responseHeader = (SendMessageResponseHeader)response.readCustomHeader();
 8 
 9     response.setOpaque(request.getOpaque());
10 
11     response.addExtField(MessageConst.PROPERTY_MSG_REGION, this.brokerController.getBrokerConfig().getRegionId());
12     response.addExtField(MessageConst.PROPERTY_TRACE_SWITCH, String.valueOf(this.brokerController.getBrokerConfig().isTraceOn()));
13 
14     log.debug("receive SendMessage request command, {}", request);
15 
16     final long startTimstamp = this.brokerController.getBrokerConfig().getStartAcceptSendRequestTimeStamp();
17     if (this.brokerController.getMessageStore().now() < startTimstamp) {
18         response.setCode(ResponseCode.SYSTEM_ERROR);
19         response.setRemark(String.format("broker unable to service, until %s", UtilAll.timeMillisToHumanString2(startTimstamp)));
20         return response;
21     }
22 
23     response.setCode(-1);
24     super.msgCheck(ctx, requestHeader, response);
25     if (response.getCode() != -1) {
26         return response;
27     }
28 
29     final byte[] body = request.getBody();
30 
31     int queueIdInt = requestHeader.getQueueId();
32     TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
33 
34     if (queueIdInt < 0) {
35         queueIdInt = Math.abs(this.random.nextInt() % 99999999) % topicConfig.getWriteQueueNums();
36     }
37 
38     MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
39     msgInner.setTopic(requestHeader.getTopic());
40     msgInner.setQueueId(queueIdInt);
41 
42     if (!handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig)) {
43         return response;
44     }
45 
46     msgInner.setBody(body);
47     msgInner.setFlag(requestHeader.getFlag());
48     MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties()));
49     msgInner.setPropertiesString(requestHeader.getProperties());
50     msgInner.setBornTimestamp(requestHeader.getBornTimestamp());
51     msgInner.setBornHost(ctx.channel().remoteAddress());
52     msgInner.setStoreHost(this.getStoreHost());
53     msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes());
54     PutMessageResult putMessageResult = null;
55     Map<String, String> oriProps = MessageDecoder.string2messageProperties(requestHeader.getProperties());
56     String traFlag = oriProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED);
57     if (traFlag != null && Boolean.parseBoolean(traFlag)) {
58         if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {
59             response.setCode(ResponseCode.NO_PERMISSION);
60             response.setRemark(
61                 "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()
62                     + "] sending transaction message is forbidden");
63             return response;
64         }
65         putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);
66     } else {
67         putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
68     }
69 
70     return handlePutMessageResult(putMessageResult, response, request, msgInner, responseHeader, sendMessageContext, ctx, queueIdInt);
71 
72 }

这里首先会把具体的消息及其相关信息封装在MessageExtBrokerInner中

MessageExtBrokerInner继承自Message，详见

【RocketMQ中Producer消息的发送源码分析】

之后会对消息的PROPERTY_TRANSACTION_PREPARED属性进行检查，判断是否是事务消息

若是事务消息，会检查是否设置了拒绝事务消息的配置rejectTransactionMessage
若是拒绝则返回相应响应response，由Netty发送给Producer
否则调用TransactionalMessageService的prepareMessage方法

若不是事务消息则调用MessageStore的putMessage方法

在事务消息的处理里，实际上只是对MessageExtBrokerInner设置相应的属性，最后还是调用putMessage方法：

 1 public PutMessageResult prepareMessage(MessageExtBrokerInner messageInner) {
 2     return transactionalMessageBridge.putHalfMessage(messageInner);
 3 }
 4 
 5 public PutMessageResult putHalfMessage(MessageExtBrokerInner messageInner) {
 6     return store.putMessage(parseHalfMessageInner(messageInner));
 7 }
 8 
 9 private MessageExtBrokerInner parseHalfMessageInner(MessageExtBrokerInner msgInner) {
10     MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_TOPIC, msgInner.getTopic());
11     MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_QUEUE_ID,
12         String.valueOf(msgInner.getQueueId()));
13     msgInner.setSysFlag(
14         MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), MessageSysFlag.TRANSACTION_NOT_TYPE));
15     msgInner.setTopic(TransactionalMessageUtil.buildHalfTopic());
16     msgInner.setQueueId(0);
17     msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgInner.getProperties()));
18     return msgInner;
19 }

DefaultMessageStore的putMessage方法：

 1 public PutMessageResult putMessage(MessageExtBrokerInner msg) {
 2     if (this.shutdown) {
 3         log.warn("message store has shutdown, so putMessage is forbidden");
 4         return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
 5     }
 6 
 7     if (BrokerRole.SLAVE == this.messageStoreConfig.getBrokerRole()) {
 8         long value = this.printTimes.getAndIncrement();
 9         if ((value % 50000) == 0) {
10             log.warn("message store is slave mode, so putMessage is forbidden ");
11         }
12 
13         return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
14     }
15 
16     if (!this.runningFlags.isWriteable()) {
17         long value = this.printTimes.getAndIncrement();
18         if ((value % 50000) == 0) {
19             log.warn("message store is not writeable, so putMessage is forbidden " + this.runningFlags.getFlagBits());
20         }
21 
22         return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
23     } else {
24         this.printTimes.set(0);
25     }
26 
27     if (msg.getTopic().length() > Byte.MAX_VALUE) {
28         log.warn("putMessage message topic length too long " + msg.getTopic().length());
29         return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, null);
30     }
31 
32     if (msg.getPropertiesString() != null && msg.getPropertiesString().length() > Short.MAX_VALUE) {
33         log.warn("putMessage message properties length too long " + msg.getPropertiesString().length());
34         return new PutMessageResult(PutMessageStatus.PROPERTIES_SIZE_EXCEEDED, null);
35     }
36 
37     if (this.isOSPageCacheBusy()) {
38         return new PutMessageResult(PutMessageStatus.OS_PAGECACHE_BUSY, null);
39     }
40 
41     long beginTime = this.getSystemClock().now();
42     PutMessageResult result = this.commitLog.putMessage(msg);
43 
44     long eclipseTime = this.getSystemClock().now() - beginTime;
45     if (eclipseTime > 500) {
46         log.warn("putMessage not in lock eclipse time(ms)={}, bodyLength={}", eclipseTime, msg.getBody().length);
47     }
48     this.storeStatsService.setPutMessageEntireTimeMax(eclipseTime);
49 
50     if (null == result || !result.isOk()) {
51         this.storeStatsService.getPutMessageFailedTimes().incrementAndGet();
52     }
53 
54     return result;
55 }

这里会对消息的合法性以及Broker的状态做一系列的检查，在全部通过后才继续，否则返回带有相应提示的响应

其中会检查Broker是否是SLAVE
若是SLAVE，会返回SERVICE_NOT_AVAILABLE，不允许Slave直接存储来自Producer的消息，间接说明了Master和Slave的主从关系

满足所有条件后，调用commitLog的putMessage方法：

  1 public PutMessageResult putMessage(final MessageExtBrokerInner msg) {
  2     // Set the storage time
  3     msg.setStoreTimestamp(System.currentTimeMillis());
  4     // Set the message body BODY CRC (consider the most appropriate setting
  5     // on the client)
  6     msg.setBodyCRC(UtilAll.crc32(msg.getBody()));
  7     // Back to Results
  8     AppendMessageResult result = null;
  9 
 10     StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService();
 11 
 12     String topic = msg.getTopic();
 13     int queueId = msg.getQueueId();
 14 
 15     final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag());
 16     if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE
 17         || tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) {
 18         // Delay Delivery
 19         if (msg.getDelayTimeLevel() > 0) {
 20             if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) {
 21                 msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel());
 22             }
 23 
 24             topic = ScheduleMessageService.SCHEDULE_TOPIC;
 25             queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel());
 26 
 27             // Backup real topic, queueId
 28             MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic());
 29             MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId()));
 30             msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties()));
 31 
 32             msg.setTopic(topic);
 33             msg.setQueueId(queueId);
 34         }
 35     }
 36 
 37     long eclipseTimeInLock = 0;
 38     MappedFile unlockMappedFile = null;
 39     MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();
 40 
 41     putMessageLock.lock(); //spin or ReentrantLock ,depending on store config
 42     try {
 43         long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now();
 44         this.beginTimeInLock = beginLockTimestamp;
 45 
 46         // Here settings are stored timestamp, in order to ensure an orderly
 47         // global
 48         msg.setStoreTimestamp(beginLockTimestamp);
 49 
 50         if (null == mappedFile || mappedFile.isFull()) {
 51             mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise
 52         }
 53         if (null == mappedFile) {
 54             log.error("create mapped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
 55             beginTimeInLock = 0;
 56             return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null);
 57         }
 58 
 59         result = mappedFile.appendMessage(msg, this.appendMessageCallback);
 60         switch (result.getStatus()) {
 61             case PUT_OK:
 62                 break;
 63             case END_OF_FILE:
 64                 unlockMappedFile = mappedFile;
 65                 // Create a new file, re-write the message
 66                 mappedFile = this.mappedFileQueue.getLastMappedFile(0);
 67                 if (null == mappedFile) {
 68                     // XXX: warn and notify me
 69                     log.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
 70                     beginTimeInLock = 0;
 71                     return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result);
 72                 }
 73                 result = mappedFile.appendMessage(msg, this.appendMessageCallback);
 74                 break;
 75             case MESSAGE_SIZE_EXCEEDED:
 76             case PROPERTIES_SIZE_EXCEEDED:
 77                 beginTimeInLock = 0;
 78                 return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, result);
 79             case UNKNOWN_ERROR:
 80                 beginTimeInLock = 0;
 81                 return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
 82             default:
 83                 beginTimeInLock = 0;
 84                 return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
 85         }
 86 
 87         eclipseTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp;
 88         beginTimeInLock = 0;
 89     } finally {
 90         putMessageLock.unlock();
 91     }
 92 
 93     if (eclipseTimeInLock > 500) {
 94         log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", eclipseTimeInLock, msg.getBody().length, result);
 95     }
 96 
 97     if (null != unlockMappedFile && this.defaultMessageStore.getMessageStoreConfig().isWarmMapedFileEnable()) {
 98         this.defaultMessageStore.unlockMappedFile(unlockMappedFile);
 99     }
100 
101     PutMessageResult putMessageResult = new PutMessageResult(PutMessageStatus.PUT_OK, result);
102 
103     // Statistics
104     storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet();
105     storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes());
106 
107     handleDiskFlush(result, putMessageResult, msg);
108     handleHA(result, putMessageResult, msg);
109 
110     return putMessageResult;
111 }

这里会通过mappedFileQueue的getLastMappedFile方法，找到CommitLog文件对应的映射MappedFile

关于MappedFile，及其一些操作，在【RocketMQ中Broker的启动源码分析（二）】中关于消息的调度时分析过了，这里涉及到就不再累赘

然后调用MappedFile的appendMessage方法，其中参数appendMessageCallback，是在CommitLog构造时设置的，其是实现类是CommitLog的内部类，用于后面appendMessage操作的回调在CommitLog中进行

MappedFile的appendMessage方法：

 1 public AppendMessageResult appendMessage(final MessageExtBrokerInner msg, final AppendMessageCallback cb) {
 2     return appendMessagesInner(msg, cb);
 3 }
 4 
 5 public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb) {
 6     assert messageExt != null;
 7     assert cb != null;
 8 
 9     int currentPos = this.wrotePosition.get();
10 
11     if (currentPos < this.fileSize) {
12         ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice();
13         byteBuffer.position(currentPos);
14         AppendMessageResult result = null;
15         if (messageExt instanceof MessageExtBrokerInner) {
16             result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBrokerInner) messageExt);
17         } else if (messageExt instanceof MessageExtBatch) {
18             result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBatch) messageExt);
19         } else {
20             return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
21         }
22         this.wrotePosition.addAndGet(result.getWroteBytes());
23         this.storeTimestamp = result.getStoreTimestamp();
24         return result;
25     }
26     log.error("MappedFile.appendMessage return null, wrotePosition: {} fileSize: {}", currentPos, this.fileSize);
27     return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
28 }

在这里要注意这一步：

1 ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice();

可以得到一个共享的子缓冲区ByteBuffer
稍微提一下，只有当Broker使用异步刷盘并且开启内存字节缓冲区的情况下，writeBuffer才有意义，否则都是mappedByteBuffer
后续再介绍

然后调用刚才设置的回调接口的doAppend方法：

  1 public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
  2     final MessageExtBrokerInner msgInner) {
  3     // STORETIMESTAMP + STOREHOSTADDRESS + OFFSET <br>
  4 
  5     // PHY OFFSET
  6     long wroteOffset = fileFromOffset + byteBuffer.position();
  7 
  8     this.resetByteBuffer(hostHolder, 8);
  9     String msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(hostHolder), wroteOffset);
 10 
 11     // Record ConsumeQueue information
 12     keyBuilder.setLength(0);
 13     keyBuilder.append(msgInner.getTopic());
 14     keyBuilder.append('-');
 15     keyBuilder.append(msgInner.getQueueId());
 16     String key = keyBuilder.toString();
 17     Long queueOffset = CommitLog.this.topicQueueTable.get(key);
 18     if (null == queueOffset) {
 19         queueOffset = 0L;
 20         CommitLog.this.topicQueueTable.put(key, queueOffset);
 21     }
 22 
 23     // Transaction messages that require special handling
 24     final int tranType = MessageSysFlag.getTransactionValue(msgInner.getSysFlag());
 25     switch (tranType) {
 26         // Prepared and Rollback message is not consumed, will not enter the
 27         // consumer queuec
 28         case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
 29         case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
 30             queueOffset = 0L;
 31             break;
 32         case MessageSysFlag.TRANSACTION_NOT_TYPE:
 33         case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
 34         default:
 35             break;
 36     }
 37 
 38     /**
 39      * Serialize message
 40      */
 41     final byte[] propertiesData =
 42         msgInner.getPropertiesString() == null ? null : msgInner.getPropertiesString().getBytes(MessageDecoder.CHARSET_UTF8);
 43 
 44     final int propertiesLength = propertiesData == null ? 0 : propertiesData.length;
 45 
 46     if (propertiesLength > Short.MAX_VALUE) {
 47         log.warn("putMessage message properties length too long. length={}", propertiesData.length);
 48         return new AppendMessageResult(AppendMessageStatus.PROPERTIES_SIZE_EXCEEDED);
 49     }
 50 
 51     final byte[] topicData = msgInner.getTopic().getBytes(MessageDecoder.CHARSET_UTF8);
 52     final int topicLength = topicData.length;
 53 
 54     final int bodyLength = msgInner.getBody() == null ? 0 : msgInner.getBody().length;
 55 
 56     final int msgLen = calMsgLength(bodyLength, topicLength, propertiesLength);
 57 
 58     // Exceeds the maximum message
 59     if (msgLen > this.maxMessageSize) {
 60         CommitLog.log.warn("message size exceeded, msg total size: " + msgLen + ", msg body size: " + bodyLength
 61             + ", maxMessageSize: " + this.maxMessageSize);
 62         return new AppendMessageResult(AppendMessageStatus.MESSAGE_SIZE_EXCEEDED);
 63     }
 64 
 65     // Determines whether there is sufficient free space
 66     if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) {
 67         this.resetByteBuffer(this.msgStoreItemMemory, maxBlank);
 68         // 1 TOTALSIZE
 69         this.msgStoreItemMemory.putInt(maxBlank);
 70         // 2 MAGICCODE
 71         this.msgStoreItemMemory.putInt(CommitLog.BLANK_MAGIC_CODE);
 72         // 3 The remaining space may be any value
 73         // Here the length of the specially set maxBlank
 74         final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
 75         byteBuffer.put(this.msgStoreItemMemory.array(), 0, maxBlank);
 76         return new AppendMessageResult(AppendMessageStatus.END_OF_FILE, wroteOffset, maxBlank, msgId, msgInner.getStoreTimestamp(),
 77             queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills);
 78     }
 79 
 80     // Initialization of storage space
 81     this.resetByteBuffer(msgStoreItemMemory, msgLen);
 82     // 1 TOTALSIZE
 83     this.msgStoreItemMemory.putInt(msgLen);
 84     // 2 MAGICCODE
 85     this.msgStoreItemMemory.putInt(CommitLog.MESSAGE_MAGIC_CODE);
 86     // 3 BODYCRC
 87     this.msgStoreItemMemory.putInt(msgInner.getBodyCRC());
 88     // 4 QUEUEID
 89     this.msgStoreItemMemory.putInt(msgInner.getQueueId());
 90     // 5 FLAG
 91     this.msgStoreItemMemory.putInt(msgInner.getFlag());
 92     // 6 QUEUEOFFSET
 93     this.msgStoreItemMemory.putLong(queueOffset);
 94     // 7 PHYSICALOFFSET
 95     this.msgStoreItemMemory.putLong(fileFromOffset + byteBuffer.position());
 96     // 8 SYSFLAG
 97     this.msgStoreItemMemory.putInt(msgInner.getSysFlag());
 98     // 9 BORNTIMESTAMP
 99     this.msgStoreItemMemory.putLong(msgInner.getBornTimestamp());
100     // 10 BORNHOST
101     this.resetByteBuffer(hostHolder, 8);
102     this.msgStoreItemMemory.put(msgInner.getBornHostBytes(hostHolder));
103     // 11 STORETIMESTAMP
104     this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp());
105     // 12 STOREHOSTADDRESS
106     this.resetByteBuffer(hostHolder, 8);
107     this.msgStoreItemMemory.put(msgInner.getStoreHostBytes(hostHolder));
108     //this.msgBatchMemory.put(msgInner.getStoreHostBytes());
109     // 13 RECONSUMETIMES
110     this.msgStoreItemMemory.putInt(msgInner.getReconsumeTimes());
111     // 14 Prepared Transaction Offset
112     this.msgStoreItemMemory.putLong(msgInner.getPreparedTransactionOffset());
113     // 15 BODY
114     this.msgStoreItemMemory.putInt(bodyLength);
115     if (bodyLength > 0)
116         this.msgStoreItemMemory.put(msgInner.getBody());
117     // 16 TOPIC
118     this.msgStoreItemMemory.put((byte) topicLength);
119     this.msgStoreItemMemory.put(topicData);
120     // 17 PROPERTIES
121     this.msgStoreItemMemory.putShort((short) propertiesLength);
122     if (propertiesLength > 0)
123         this.msgStoreItemMemory.put(propertiesData);
124 
125     final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
126     // Write messages to the queue buffer
127     byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen);
128 
129     AppendMessageResult result = new AppendMessageResult(AppendMessageStatus.PUT_OK, wroteOffset, msgLen, msgId,
130         msgInner.getStoreTimestamp(), queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills);
131 
132     switch (tranType) {
133         case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
134         case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
135             break;
136         case MessageSysFlag.TRANSACTION_NOT_TYPE:
137         case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
138             // The next update ConsumeQueue information
139             CommitLog.this.topicQueueTable.put(key, ++queueOffset);
140             break;
141         default:
142             break;
143     }
144     return result;
145 }

这里首先会根据fileFromOffset和byteBuffer的position计算出实际要往文件写入时的Offset，使用wroteOffset记录

之后根据MessageExtBrokerInner中的内容，按照CommitLog文件的消息结构，通过put操作将消息缓存在msgStoreItemMemory这个ByteBuffer中

CommitLog文件中消息的结构：

然后通过：

1 byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen);

将msgStoreItemMemory中的信息缓存到刚才获取的这个共享ByteBuffer中

其中：

 1 if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) {
 2    this.resetByteBuffer(this.msgStoreItemMemory, maxBlank);
 3    // 1 TOTALSIZE
 4    this.msgStoreItemMemory.putInt(maxBlank);
 5    // 2 MAGICCODE
 6    this.msgStoreItemMemory.putInt(CommitLog.BLANK_MAGIC_CODE);
 7    // 3 The remaining space may be any value
 8    // Here the length of the specially set maxBlank
 9    final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
10    byteBuffer.put(this.msgStoreItemMemory.array(), 0, maxBlank);
11    return new AppendMessageResult(AppendMessageStatus.END_OF_FILE, wroteOffset, maxBlank, msgId, msgInner.getStoreTimestamp(),
12        queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills);
13 }

会检查当前CommitLog文件是否有可用空间，CommitLog结尾会以BLANK（8字节）的形式出现
这里可以看到BLANK的结构，由4字节maxBlank（fileSize-currentPos）以及4字节魔数构成
文件空间不可用会返回END_OF_FILE状态信息，之后会有用

回到appendMessagesInner方法，在完成doAppend后，根据往缓冲区写入的数据大小，修改wrotePosition这个AtomicInteger值，以便下次的定位

再回到CommitLog的putMessage方法：

 1 result = mappedFile.appendMessage(msg, this.appendMessageCallback);
 2 switch (result.getStatus()) {
 3     case PUT_OK:
 4         break;
 5     case END_OF_FILE:
 6         unlockMappedFile = mappedFile;
 7         // Create a new file, re-write the message
 8         mappedFile = this.mappedFileQueue.getLastMappedFile(0);
 9         if (null == mappedFile) {
10             // XXX: warn and notify me
11             log.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
12             beginTimeInLock = 0;
13             return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result);
14         }
15         result = mappedFile.appendMessage(msg, this.appendMessageCallback);
16         break;
17     case MESSAGE_SIZE_EXCEEDED:
18     case PROPERTIES_SIZE_EXCEEDED:
19         beginTimeInLock = 0;
20         return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, result);
21     case UNKNOWN_ERROR:
22         beginTimeInLock = 0;
23         return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
24     default:
25         beginTimeInLock = 0;
26         return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
27 }

在得到result后，会进行状态检查

其中若是刚才说都END_OF_FILE状态
则会通过mappedFileQueue的getLastMappedFile方法，创建一个新的CommitLog文件以及文件映射MappedFile
然后调用这个新的MappedFile的appendMessage方法，重复之前的步骤，这样就会将消息往新的ByteBuffer中，而之前的那个则缓存着8字节的BLANK

到这里SendMessageProcessor的任务其实已经完成的差不多了，但是，按照我上面的分析来看，仅仅只是将消息进行了缓存，并没有真正地写入磁盘完成持久化

在CommitLog的putMessage方法最后还有两步非常重要的操作：

1 handleDiskFlush(result, putMessageResult, msg);
2 handleHA(result, putMessageResult, msg);

handleHA在后续分析主从复制时再说

那么重点是这个handleDiskFlush方法：

 1 public void handleDiskFlush(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) {
 2     // Synchronization flush
 3     if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) {
 4         final GroupCommitService service = (GroupCommitService) this.flushCommitLogService;
 5         if (messageExt.isWaitStoreMsgOK()) {
 6             GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
 7             service.putRequest(request);
 8             boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
 9             if (!flushOK) {
10                 log.error("do groupcommit, wait for flush failed, topic: " + messageExt.getTopic() + " tags: " + messageExt.getTags()
11                     + " client address: " + messageExt.getBornHostString());
12                 putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT);
13             }
14         } else {
15             service.wakeup();
16         }
17     }
18     // Asynchronous flush
19     else {
20         if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) {
21             flushCommitLogService.wakeup();
22         } else {
23             commitLogService.wakeup();
24         }
25     }
26 }

这里的话就会涉及到Broker的CommitLog刷盘

关于CommitLog刷盘我会在下一篇博客详细分析，这里我就简单说一下

Broker的CommitLog刷盘会启动一个线程，不停地将缓冲区的内容写入磁盘（CommitLog文件）中，主要分为异步刷盘和同步刷盘

异步刷盘又可以分为两种方式：
①缓存到mappedByteBuffer -> 写入磁盘（包括同步刷盘）
②缓存到writeBuffer -> 缓存到fileChannel -> 写入磁盘（前面说过的开启内存字节缓冲区情况下）

也就是说Broker在接收到Producer的消息时，并没有同时将消息持久化，而是进行缓存记录，然后通过刷盘线程，将缓存写入磁盘完成持久化

在上一篇博客我还详细分析过消息调度
结合着来看，在刷盘线程工作的同时，调度线程也在从磁盘读取消息到内存，将消息进行分配，刷盘线程也会随时写入新消息，二者相互协调

RocketMQ的工作原理到这已经初见端倪，后续重点会分析消费者的消费（Pull、Push），以及主从复制

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原文地址：https://www.cnblogs.com/a526583280/p/11306645.html