两篇精彩的文章：
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rocketmq通过netty获取到消息请求后，直接掉处理模块，比如：SendMessageProcessor
这个处理类主要负责处理客户端发送消息的请求。
这个类实现了com.alibaba.rocketmq.remoting.netty.NettyRequestProcessor接口。这个接口下一共两个方法：
RemotingCommand processRequest(ChannelHandlerContext ctx, RemotingCommand request) throws Exception; boolean rejectRequest();
加粗的方法是我们接下来要讲的方法。
它同时还继承了com.alibaba.rocketmq.broker.processor.AbstractSendMessageProcessor。
我们先看一下这个过程的调用链：
这里有一篇博客写的特别好：http://www.cnblogs.com/sunshine-2015/p/6291116.html
再次基础之上补充一点点东西。
首先进入SendMessageProcessor类的第一个方法是：
这个类什么时候被调用的呢？肯定是netty通信模块接收到消息后调用了，具体实在这里：
就是箭头所指的地方调用的上面那个方法。
我们看一下完整的从netty通信模块接收消息到这里的整个过程：
现在就到了我们非常熟悉的Handler了。
这里从下往上看会更加的直观。
好了，我们接着往消息存储走。
我们进入这个方法：
private RemotingCommand sendMessage(final ChannelHandlerContext ctx, // final RemotingCommand request, // final SendMessageContext sendMessageContext, // final SendMessageRequestHeader requestHeader) throws RemotingCommandException { 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()); if (log.isDebugEnabled()) { 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); super.msgCheck(ctx, requestHeader, response); if (response.getCode() != -1) { return response; } final byte[] body = request.getBody(); int queueIdInt = requestHeader.getQueueId(); TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic()); if (queueIdInt < 0) { queueIdInt = Math.abs(this.random.nextInt() % 99999999) % topicConfig.getWriteQueueNums(); } int sysFlag = requestHeader.getSysFlag(); if (TopicFilterType.MULTI_TAG == topicConfig.getTopicFilterType()) { sysFlag |= MessageSysFlag.MultiTagsFlag; } String newTopic = requestHeader.getTopic(); if ((null != newTopic && newTopic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX))) { String groupName = newTopic.substring(MixAll.RETRY_GROUP_TOPIC_PREFIX.length()); SubscriptionGroupConfig subscriptionGroupConfig = this.brokerController.getSubscriptionGroupManager().findSubscriptionGroupConfig(groupName); if (null == subscriptionGroupConfig) { response.setCode(ResponseCode.SUBSCRIPTION_GROUP_NOT_EXIST); response.setRemark( "subscription group not exist, " + groupName + " " + FAQUrl.suggestTodo(FAQUrl.SUBSCRIPTION_GROUP_NOT_EXIST)); return response; } int maxReconsumeTimes = subscriptionGroupConfig.getRetryMaxTimes(); if (request.getVersion() >= MQVersion.Version.V3_4_9.ordinal()) { maxReconsumeTimes = requestHeader.getMaxReconsumeTimes(); } int reconsumeTimes = requestHeader.getReconsumeTimes(); if (reconsumeTimes >= maxReconsumeTimes) { newTopic = MixAll.getDLQTopic(groupName); queueIdInt = Math.abs(this.random.nextInt() % 99999999) % DLQ_NUMS_PER_GROUP; topicConfig = this.brokerController.getTopicConfigManager().createTopicInSendMessageBackMethod(newTopic, // DLQ_NUMS_PER_GROUP, // PermName.PERM_WRITE, 0 ); if (null == topicConfig) { response.setCode(ResponseCode.SYSTEM_ERROR); response.setRemark("topic[" + newTopic + "] not exist"); return response; } } } MessageExtBrokerInner msgInner = new MessageExtBrokerInner(); msgInner.setTopic(newTopic); msgInner.setBody(body); msgInner.setFlag(requestHeader.getFlag()); MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties())); msgInner.setPropertiesString(requestHeader.getProperties()); msgInner.setTagsCode(MessageExtBrokerInner.tagsString2tagsCode(topicConfig.getTopicFilterType(), msgInner.getTags())); msgInner.setQueueId(queueIdInt); msgInner.setSysFlag(sysFlag); msgInner.setBornTimestamp(requestHeader.getBornTimestamp()); msgInner.setBornHost(ctx.channel().remoteAddress()); msgInner.setStoreHost(this.getStoreHost()); msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes()); if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) { String traFlag = msgInner.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED); if (traFlag != null) { response.setCode(ResponseCode.NO_PERMISSION); response.setRemark( "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1() + "] sending transaction message is forbidden"); return response; } } // 前面是一些系统检查和数据准备，下面进入消息存储环节。 PutMessageResult putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner); // 锚点putMessage if (putMessageResult != null) { boolean sendOK = false; switch (putMessageResult.getPutMessageStatus()) { // Success case PUT_OK: sendOK = true; response.setCode(ResponseCode.SUCCESS); break; case FLUSH_DISK_TIMEOUT: response.setCode(ResponseCode.FLUSH_DISK_TIMEOUT); sendOK = true; break; case FLUSH_SLAVE_TIMEOUT: response.setCode(ResponseCode.FLUSH_SLAVE_TIMEOUT); sendOK = true; break; case SLAVE_NOT_AVAILABLE: response.setCode(ResponseCode.SLAVE_NOT_AVAILABLE); sendOK = true; break; // Failed case CREATE_MAPEDFILE_FAILED: response.setCode(ResponseCode.SYSTEM_ERROR); response.setRemark("create maped file failed, please make sure OS and JDK both 64bit."); break; case MESSAGE_ILLEGAL: case PROPERTIES_SIZE_EXCEEDED: response.setCode(ResponseCode.MESSAGE_ILLEGAL); response.setRemark( "the message is illegal, maybe msg body or properties length not matched. msg body length limit 128k, msg properties length limit 32k."); break; case SERVICE_NOT_AVAILABLE: response.setCode(ResponseCode.SERVICE_NOT_AVAILABLE); response.setRemark( "service not available now, maybe disk full, " + diskUtil() + ", maybe your broker machine memory too small."); break; case OS_PAGECACHE_BUSY: response.setCode(ResponseCode.SYSTEM_ERROR); response.setRemark("[PC_SYNCHRONIZED]broker busy, start flow control for a while"); break; case UNKNOWN_ERROR: response.setCode(ResponseCode.SYSTEM_ERROR); response.setRemark("UNKNOWN_ERROR"); break; default: response.setCode(ResponseCode.SYSTEM_ERROR); response.setRemark("UNKNOWN_ERROR DEFAULT"); break; } String owner = request.getExtFields().get(BrokerStatsManager.COMMERCIAL_OWNER); if (sendOK) { this.brokerController.getBrokerStatsManager().incTopicPutNums(msgInner.getTopic()); this.brokerController.getBrokerStatsManager().incTopicPutSize(msgInner.getTopic(), putMessageResult.getAppendMessageResult().getWroteBytes()); this.brokerController.getBrokerStatsManager().incBrokerPutNums(); response.setRemark(null); responseHeader.setMsgId(putMessageResult.getAppendMessageResult().getMsgId()); responseHeader.setQueueId(queueIdInt); responseHeader.setQueueOffset(putMessageResult.getAppendMessageResult().getLogicsOffset()); doResponse(ctx, request, response); if (hasSendMessageHook()) { sendMessageContext.setMsgId(responseHeader.getMsgId()); sendMessageContext.setQueueId(responseHeader.getQueueId()); sendMessageContext.setQueueOffset(responseHeader.getQueueOffset()); int wroteSize = putMessageResult.getAppendMessageResult().getWroteBytes(); int incValue = (int) Math.ceil(wroteSize / BrokerStatsManager.SIZE_PER_COUNT); sendMessageContext.setCommercialSendStats(BrokerStatsManager.StatsType.SEND_SUCCESS); sendMessageContext.setCommercialSendTimes(incValue); sendMessageContext.setCommercialSendSize(wroteSize); sendMessageContext.setCommercialOwner(owner); } return null; } else { if (hasSendMessageHook()) { int wroteSize = request.getBody().length; int incValue = (int) Math.ceil(wroteSize / BrokerStatsManager.SIZE_PER_COUNT); sendMessageContext.setCommercialSendStats(BrokerStatsManager.StatsType.SEND_FAILURE); sendMessageContext.setCommercialSendTimes(incValue); sendMessageContext.setCommercialSendSize(wroteSize); sendMessageContext.setCommercialOwner(owner); } } } else { response.setCode(ResponseCode.SYSTEM_ERROR); response.setRemark("store putMessage return null"); } return response; } 我们进入PutMessageResult putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
的MessageStore.putMessage(msgInner)方法。
MesageStore这个接口一共有三个实现类：
实现了上面那个方法的只有DefaultMessageStore实现类。所以我们看DefaultMessageStore.putMessage(MessageExtBrokerInner msg)方法。
public PutMessageResult putMessage(MessageExtBrokerInner msg) { 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); } // message topic长度校验 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); } // message properties长度校验 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(); //上面是一些系统检查，下面是消息的存储 PutMessageResult result = this.commitLog.putMessage(msg); // 性能数据统计 long eclipseTime = this.getSystemClock().now() - beginTime; if (eclipseTime > 1000) { log.warn("putMessage not in lock eclipse time(ms)={}, bodyLength={}", eclipseTime, msg.getBody().length); } this.storeStatsService.setPutMessageEntireTimeMax(eclipseTime); if (null == result || !result.isOk()) { this.storeStatsService.getPutMessageFailedTimes().incrementAndGet(); } return result; } 其中commitLog在构造方法中的初始化：this.commitLog = new CommitLog(this);
我们接着进入commitLog.putMessage(final MessageExtBrokerInner msg)
这个方法搞定了，你也就彻底了解了rocketmq的消息存储过程了。
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.TransactionNotType// || tranType == MessageSysFlag.TransactionCommitType) { // Delay Delivery if (msg.getDelayTimeLevel() > 0) { if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) { msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()); } topic = ScheduleMessageService.SCHEDULE_TOPIC; queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel()); // Backup real topic, 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())); msg.setTopic(topic); msg.setQueueId(queueId); } } long eclipseTimeInLock = 0; MapedFile unlockMapedFile = null; MapedFile mapedFile = this.mapedFileQueue.getLastMapedFileWithLock(); synchronized (this) { long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now(); this.beginTimeInLock = beginLockTimestamp; // Here settings are stored timestamp, in order to ensure an orderly // global msg.setStoreTimestamp(beginLockTimestamp); if (null == mapedFile || mapedFile.isFull()) { mapedFile = this.mapedFileQueue.getLastMapedFile(); } if (null == mapedFile) { log.error("create maped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString()); beginTimeInLock = 0; return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null); } result = mapedFile.appendMessage(msg, this.appendMessageCallback); switch (result.getStatus()) { case PUT_OK: break; case END_OF_FILE: unlockMapedFile = mapedFile; // Create a new file, re-write the message mapedFile = this.mapedFileQueue.getLastMapedFile(); if (null == mapedFile) { // XXX: warn and notify me log.error("create maped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString()); beginTimeInLock = 0; return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result); } result = mapedFile.appendMessage(msg, this.appendMessageCallback); break; case MESSAGE_SIZE_EXCEEDED: 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); } eclipseTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp; beginTimeInLock = 0; } // end of synchronized if (eclipseTimeInLock > 1000) { log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", eclipseTimeInLock, msg.getBody().length, result); } if (null != unlockMapedFile) { this.defaultMessageStore.unlockMapedFile(unlockMapedFile); } PutMessageResult putMessageResult = new PutMessageResult(PutMessageStatus.PUT_OK, result); // Statistics storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet(); storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes()); GroupCommitRequest request = null; // Synchronization flush if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) { GroupCommitService service = (GroupCommitService) this.flushCommitLogService; if (msg.isWaitStoreMsgOK()) { request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes()); service.putRequest(request); boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout()); if (!flushOK) { log.error("do groupcommit, wait for flush failed, topic: " + msg.getTopic() + " tags: " + msg.getTags() + " client address: " + msg.getBornHostString()); putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT); } } else { service.wakeup(); } } // Asynchronous flush else { this.flushCommitLogService.wakeup(); } // Synchronous write double if (BrokerRole.SYNC_MASTER == this.defaultMessageStore.getMessageStoreConfig().getBrokerRole()) { HAService service = this.defaultMessageStore.getHaService(); if (msg.isWaitStoreMsgOK()) { // Determine whether to wait if (service.isSlaveOK(result.getWroteOffset() + result.getWroteBytes())) { if (null == request) { request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes()); } service.putRequest(request); service.getWaitNotifyObject().wakeupAll(); boolean flushOK = // TODO request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout()); if (!flushOK) { log.error("do sync transfer other node, wait return, but failed, topic: " + msg.getTopic() + " tags: " + msg.getTags() + " client address: " + msg.getBornHostString()); putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_SLAVE_TIMEOUT); } } // Slave problem else { // Tell the producer, slave not available putMessageResult.setPutMessageStatus(PutMessageStatus.SLAVE_NOT_AVAILABLE); } } } return putMessageResult; } 我们进入标黄的方法：
/** * 插入消息到 MappedFile，并返回插入结果。 * MappedFile的理解就可以按照字面意思来理解。换一种说法就是file的缓冲区。刷盘之前先写入缓存区。nio就是这样的。 * @param msg * @param cb * @return */ public AppendMessageResult appendMessage(final Object msg, final AppendMessageCallback cb) { assert msg != null; assert cb != null; int currentPos = this.wrotePostion.get(); if (currentPos < this.fileSize) { // 获取需要写入的字节缓冲区。为什么会有 writeBuffer != null 的判断后，使用不同的字节缓冲区，见：FlushCommitLogService。 ByteBuffer byteBuffer = this.mappedByteBuffer.slice(); byteBuffer.position(currentPos); AppendMessageResult result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, msg); this.wrotePostion.addAndGet(result.getWroteBytes()); this.storeTimestamp = result.getStoreTimestamp(); return result; } log.error("MapedFile.appendMessage return null, wrotePostion: " + currentPos + " fileSize: " + this.fileSize); return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR); } 接着看上面这个标黄的方法：
public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank, final Object msg) { // STORETIMESTAMP + STOREHOSTADDRESS + OFFSET MessageExtBrokerInner msgInner = (MessageExtBrokerInner) msg; // PHY OFFSET long wroteOffset = fileFromOffset + byteBuffer.position(); String msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(), wroteOffset); // Record ConsumeQueue information String key = msgInner.getTopic() + "-" + msgInner.getQueueId(); 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.TransactionPreparedType: case MessageSysFlag.TransactionRollbackType: queueOffset = 0L; break; case MessageSysFlag.TransactionNotType: case MessageSysFlag.TransactionCommitType: default: break; } /** * Serialize message 序列化消息 */ final byte[] propertiesData = msgInner.getPropertiesString() == null ? null : msgInner.getPropertiesString().getBytes(MessageDecoder.CHARSET_UTF8); if (propertiesData.length > Short.MAX_VALUE) { log.warn("putMessage message properties length too long. length={}", propertiesData.length); return new AppendMessageResult(AppendMessageStatus.PROPERTIES_SIZE_EXCEEDED); } final short propertiesLength = propertiesData == null ? 0 : (short) propertiesData.length; final byte[] topicData = msgInner.getTopic().getBytes(MessageDecoder.CHARSET_UTF8); final int topicLength = topicData == null ? 0 : topicData.length; final int bodyLength = msgInner.getBody() == null ? 0 : msgInner.getBody().length; final int msgLen = calMsgLength(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); } // Determines whether there is sufficient free space // 确定是否有足够的空间 if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) { this.resetMsgStoreItemMemory(maxBlank); // 1 TOTALSIZE this.msgStoreItemMemory.putInt(maxBlank); // 2 MAGICCODE this.msgStoreItemMemory.putInt(CommitLog.BlankMagicCode); // 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.resetMsgStoreItemMemory(msgLen); // 1 TOTALSIZE this.msgStoreItemMemory.putInt(msgLen); // 2 MAGICCODE this.msgStoreItemMemory.putInt(CommitLog.MessageMagicCode); // 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.msgStoreItemMemory.put(msgInner.getBornHostBytes()); // 11 STORETIMESTAMP this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp()); // 12 STOREHOSTADDRESS this.msgStoreItemMemory.put(msgInner.getStoreHostBytes()); // 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(propertiesLength); if (propertiesLength > 0) this.msgStoreItemMemory.put(propertiesData); final long beginTimeMills = CommitLog.this.defaultMessageStore.now(); // message:>>>>>>>:Hello RocketMQ 0 System.out.println("message:>>>>>>>:" + new String(msgInner.getBody())); // Write messages to the queue buffer byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen); AppendMessageResult result = new AppendMessageResult(AppendMessageStatus.PUT_OK, wroteOffset, msgLen, msgId, msgInner.getStoreTimestamp(), queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills); switch (tranType) { case MessageSysFlag.TransactionPreparedType: case MessageSysFlag.TransactionRollbackType: break; case MessageSysFlag.TransactionNotType: case MessageSysFlag.TransactionCommitType: // The next update ConsumeQueue information CommitLog.this.topicQueueTable.put(key, ++queueOffset); break; default: break; } return result; } private void resetMsgStoreItemMemory(final int length) { this.msgStoreItemMemory.flip(); this.msgStoreItemMemory.limit(length); } } 我们注意到消息被保存到了：msgStoreItemMemory这里，这是一个内存映射文件MappedByteBuffer
可以参考（http://www.cnblogs.com/guazi/p/6829487.html）
他声明在MapedFile中，这个类我们上面说了，他的功能和他的名字正好相符。
//映射的内存对象 文件映射为的内存 private final MappedByteBuffer mappedByteBuffer;
//映射的FileChannel对象 nio阻塞 private FileChannel fileChannel;
在构造方法中初始化：
this.fileChannel = new RandomAccessFile(this.file, "rw").getChannel(); this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE, 0, fileSize);
保存到这里之后，我们回到最开始的 sendMessage方法中的锚点
消息保存的映射缓存中后，就启动耍盘线程了，同样是在sendmessage方法中，接下来就是耍盘操作了：
... ... // 消息刷盘，即持久化到文件。上面插入消息实际未存储到硬盘。此处，根据不同的刷盘策略，执行会有不同。详细解析见：FlushCommitLogService。 // 进行同步||异步 flush||commit GroupCommitRequest request = null; // Synchronization flush if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) { GroupCommitService service = (GroupCommitService) this.flushCommitLogService; if (msg.isWaitStoreMsgOK()) { request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes()); service.putRequest(request); boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout()); if (!flushOK) { log.error("do groupcommit, wait for flush failed, topic: " + msg.getTopic() + " tags: " + msg.getTags() + " client address: " + msg.getBornHostString()); putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT); } } else { service.wakeup(); } } // Asynchronous flush else { this.flushCommitLogService.wakeup();// important：唤醒commitLog线程，进行flush。具体看flushCommitLogService的实现类 } ...... 这里分成了种刷盘方式，一种是同步FlushDiskType.SYNC_FLUSH，一种是异步。
配置系统的同步和异步刷盘方式可以通过这里看到：
同步的是这个线程：GroupCommitService service = (GroupCommitService) this.flushCommitLogService;来处理刷盘逻辑。
我们直接看他的刷盘业务代码：
private void doCommit() { 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++) { flushOK = (CommitLog.this.mapedFileQueue.getCommittedWhere() >= req.getNextOffset()); if (!flushOK) { CommitLog.this.mapedFileQueue.commit(0); } } req.wakeupCustomer(flushOK); } long storeTimestamp = CommitLog.this.mapedFileQueue.getStoreTimestamp(); if (storeTimestamp > 0) { 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.mapedFileQueue.commit(0); } } 最后调用：CommitLog.this.mapedFileQueue.commit(0);来保存到硬盘。
// 消息文件队列，包含所有保存在磁盘上的文件。另外MappedFile和文件一对一关系。这两个类之间的关系非常紧密。
com.alibaba.rocketmq.store.MapedFileQueue
这个也是在 CommitLog的构造方法中初始化的。
MapedFileQueue mapedFileQueue;
this.mapedFileQueue = new MapedFileQueue(defaultMessageStore.getMessageStoreConfig().getStorePathCommitLog(), defaultMessageStore.getMessageStoreConfig().getMapedFileSizeCommitLog(), defaultMessageStore.getAllocateMapedFileService());
public MapedFileQueue(final String storePath, int mapedFileSize, AllocateMapedFileService allocateMapedFileService) { this.storePath = storePath; this.mapedFileSize = mapedFileSize; this.allocateMapedFileService = allocateMapedFileService; }
看一下commit(final int flushLeastPages)方法：
public boolean commit(final int flushLeastPages) { boolean result = true; MapedFile mapedFile = this.findMapedFileByOffset(this.committedWhere, true); if (mapedFile != null) { long tmpTimeStamp = mapedFile.getStoreTimestamp(); int offset = mapedFile.commit(flushLeastPages); long where = mapedFile.getFileFromOffset() + offset; result = (where == this.committedWhere); this.committedWhere = where; if (0 == flushLeastPages) { this.storeTimestamp = tmpTimeStamp; } } return result; }
public MapedFile findMapedFileByOffset(final long offset, final boolean returnFirstOnNotFound) { try { this.readWriteLock.readLock().lock(); MapedFile mapedFile = this.getFirstMapedFile(); if (mapedFile != null) { int index = (int) ((offset / this.mapedFileSize) - (mapedFile.getFileFromOffset() / this.mapedFileSize)); if (index < 0 || index >= this.mapedFiles.size()) { logError .warn( "findMapedFileByOffset offset not matched, request Offset: {}, index: {}, mapedFileSize: {}, mapedFiles count: {}, StackTrace: {}",// offset,// index,// this.mapedFileSize,// this.mapedFiles.size(),// UtilAll.currentStackTrace()); } try { return this.mapedFiles.get(index); } catch (Exception e) { if (returnFirstOnNotFound) { return mapedFile; } } } } catch (Exception e) { log.error("findMapedFileByOffset Exception", e); } finally { this.readWriteLock.readLock().unlock(); } return null; } private MapedFile getFirstMapedFile() { if (this.mapedFiles.isEmpty()) { return null; } return this.mapedFiles.get(0); } 最终要找到mapedFiles的赋值的方法：
就是他了！！！
com.alibaba.rocketmq.store.MapedFileQueue public boolean load() { File dir = new File(this.storePath); File[] files = dir.listFiles(); if (files != null) { // ascending order Arrays.sort(files); for (File file : files) { if (file.length() != this.mapedFileSize) { log.warn(file + "\t" + file.length() + " length not matched message store config value, ignore it"); return true; } try { MapedFile mapedFile = new MapedFile(file.getPath(), mapedFileSize); mapedFile.setWrotePostion(this.mapedFileSize); mapedFile.setCommittedPosition(this.mapedFileSize); this.mapedFiles.add(mapedFile); log.info("load " + file.getPath() + " OK"); } catch (IOException e) { log.error("load file " + file + " error", e); return false; } } } return true; } 现在来看看这个MapedFile的构造方法：
需要注意的是一个内部属性：
//文件的起始偏移量 该文件的全局offset，也就是文件名的前缀private final long fileFromOffset;
public MapedFile(final String fileName, final int fileSize) throws IOException { this.fileName = fileName; this.fileSize = fileSize; this.file = new File(fileName); this.fileFromOffset = Long.parseLong(this.file.getName()); boolean ok = false; ensureDirOK(this.file.getParent()); try { this.fileChannel = new RandomAccessFile(this.file, "rw").getChannel(); this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE, 0, fileSize); TotalMapedVitualMemory.addAndGet(fileSize); TotalMapedFiles.incrementAndGet(); ok = true; } catch (FileNotFoundException e) { log.error("create file channel " + this.fileName + " Failed. ", e); throw e; } catch (IOException e) { log.error("map file " + this.fileName + " Failed. ", e); throw e; } finally { if (!ok && this.fileChannel != null) { this.fileChannel.close(); } } } 好了回到。
int offset = mapedFile.commit(flushLeastPages)；
接着看：
/** * 消息刷盘 * * @param flushLeastPages * 至少刷几个page * * @return */ public int commit(final int flushLeastPages) { //判断当前是否能刷盘 if (this.isAbleToFlush(flushLeastPages)) { //类似于一个智能指针，控制刷盘线程数 if (this.hold()) { int value = this.wrotePostion.get(); //刷盘，内存到硬盘 this.mappedByteBuffer.force(); this.committedPosition.set(value); //释放智能指针 this.release(); } else { log.warn("in commit, hold failed, commit offset = " + this.committedPosition.get()); this.committedPosition.set(this.wrotePostion.get()); } } return this.getCommittedPosition(); } 到这来说刷盘就算结束了。当然中间跳过了很多，也是不得已的事，争取再抽时间把文章拆分一下。