消息存放到commitlog文件后，要给消费者使用，就还得把消息分发到 cq(ConsumeQueue)和 indexFile，那么怎么分发，由谁发起呢？这一章主要就把这个讲明白。Java相关的源代码调用链路都比较长，不好整条链接每行代码跟进去，只能挑重点讲，这点跟C/C++代码不同，所以我们就挑重点讲，从消息分发开始入手，在这之前先把调用链列出来，有兴趣的读者可以去看下整条链路的源码。

BrokerController.start() // Broker的启动

->DefaultMessageStore.start() // 存储消息服务启动

​ ->ReputMessageService.start() // 消息分发服务，也继承ServiceThread（实现Runnable）

ReputMessageService 既然是线程服务，那start()执行后，就直接调用 run()方法了

public void run() {
    DefaultMessageStore.log.info(this.getServiceName() + " service started");

    while (!this.isStopped()) {
        try {
            Thread.sleep(1);
            this.doReput(); // 直接看这个方法
        } catch (Exception e) {
            DefaultMessageStore.log.warn(this.getServiceName() + " service has exception. ", e);
        }
    }

    DefaultMessageStore.log.info(this.getServiceName() + " service end");
}


private void doReput() {
    // reputFromOffset 表示从哪个偏移值开始分发数据，肯定不能小于commitlog最小偏移
    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());
        // 如果小于，就从commitlog最小偏移开始
        this.reputFromOffset = DefaultMessageStore.this.commitLog.getMinOffset();
    }
    // 只要reputFromOffset 值小于 commitlog 的最大偏移则持续遍历
    for (boolean doNext = true; this.isCommitLogAvailable() && doNext; ) {
		// 默认false，忽略
        if (DefaultMessageStore.this.getMessageStoreConfig().isDuplicationEnable()
            && this.reputFromOffset >= DefaultMessageStore.this.getConfirmOffset()) {
            break;
        }
		// 取出当前 reputFromOffset 偏移到 commitlog 最大偏移期间的数据，getData就是从commitlog文件中的映射缓冲区MappedBuffer读取数据，有兴趣的可以自己进去看看
        SelectMappedBufferResult result = DefaultMessageStore.this.commitLog.getData(reputFromOffset);
        if (result != null) {
            try {
                // 起始偏移
                this.reputFromOffset = result.getStartOffset();
				// size 就是要分发的数据的大于
                for (int readSize = 0; readSize < result.getSize() && doNext; ) {
                    // 从commitlog将消息读取出来后，再拆解出来做校验，校验通过后，再组装成一个分发请求 DispatchRequest 对象，checkMessageAndReturnSize 方法里面对消息的拆解，实际就是写入消息时（看`章节11.3.4`中 doAppend方法）的反向操作
                    DispatchRequest dispatchRequest =
                        DefaultMessageStore.this.commitLog.checkMessageAndReturnSize(result.getByteBuffer(), false, false);
                    int size = dispatchRequest.getBufferSize() == -1 ? dispatchRequest.getMsgSize() : dispatchRequest.getBufferSize();

                    if (dispatchRequest.isSuccess()) { // 成功，证明消息校验通过，没有问题
                        if (size > 0) {
                            // 开始分发消息，这里分别包含了对cq和indexFile内容的分发，分别看`章节14.1`和`章节14.2`
                            DefaultMessageStore.this.doDispatch(dispatchRequest);
							// 如果是master，还需要通过消息者拉取消息等待的线程，可以开始消费了，这块内容，具体讲到消费者时再写
                            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());
                            }
						 // 分发 size 字节内容，偏移值增加
                            this.reputFromOffset += size;
                            readSize += size;
                            // slave节点
                            if (DefaultMessageStore.this.getMessageStoreConfig().getBrokerRole() == BrokerRole.SLAVE) {
                                // 统计该topic成功分发消息次数
                                DefaultMessageStore.this.storeStatsService
                                    .getSinglePutMessageTopicTimesTotal(dispatchRequest.getTopic()).incrementAndGet();
							// 统计该topic成功分发消息大小（字节）
                                DefaultMessageStore.this.storeStatsService
                                    .getSinglePutMessageTopicSizeTotal(dispatchRequest.getTopic())
                                    .addAndGet(dispatchRequest.getMsgSize());
                            }
                        } else if (size == 0) {
                            // 当前commitlog文件，没有可以分发的，再滚动到下一个commitlog文件
                            this.reputFromOffset = DefaultMessageStore.this.commitLog.rollNextFile(this.reputFromOffset);
                            readSize = result.getSize();
                        }
                    } else if (!dispatchRequest.isSuccess()) {// 不成功，就是消息校验出了问题或者消息总大小对不上

                        if (size > 0) { // 消息大小对不上
                            log.error("[BUG]read total count not equals msg total size. reputFromOffset={}", reputFromOffset);
                            this.reputFromOffset += size;
                        } else { // size <= 0 表示消息检验不通过，可以认为是非法消息，不能分发给消费者
                            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);
                                // 由于不能分发给消费者，所以这里直接跳过
                                this.reputFromOffset += result.getSize() - readSize;
                            }
                        }
                    }
                }
            } finally {
                // 资源释放
                result.release();
            }
        } else {
            doNext = false;
        }
    }
}

正式分发前，还是再解释一下，分发请求 DispatchRequest 用在哪里，由谁来用，话不多数，直接看调用链：

BrokerController.initialize()

->DefaultMessageStore构建函数

public DefaultMessageStore(final MessageStoreConfig messageStoreConfig, final BrokerStatsManager brokerStatsManager,
        final MessageArrivingListener messageArrivingListener, final BrokerConfig brokerConfig) throws IOException {
        // 省略
		
    	// 其他代码都省略了，直接看这3行代码就行，一看就懂，不解释。
        this.dispatcherList = new LinkedList<>();
    	// CommitLogDispatcherBuildConsumeQueue 对应分发到消息队列cq
        this.dispatcherList.addLast(new CommitLogDispatcherBuildConsumeQueue());
    	// CommitLogDispatcherBuildIndex 对应分发到 indexFile 
        this.dispatcherList.addLast(new CommitLogDispatcherBuildIndex());

        // 省略
    }

使用分发请求 DispatchRequest，这段源码也在 DefaultMessageStore 类中

public void doDispatch(DispatchRequest req) {
    // 遍历上面addLast添加的内容，有点像责任链模式，但又不完全是
    for (CommitLogDispatcher dispatcher : this.dispatcherList) {
        // 接下来的两节内容就是分别讲述 CommitLogDispatcherBuildConsumeQueue 和 CommitLogDispatcherBuildIndex 类的 dispatch 方法的调用了
        dispatcher.dispatch(req);
    }
}

14.1 消息队列存储

直接进 CommitLogDispatcherBuildConsumeQueue 类，这个类比较简短，就几行代码

class CommitLogDispatcherBuildConsumeQueue implements CommitLogDispatcher {

    @Override
    public void dispatch(DispatchRequest request) {
        final int tranType = MessageSysFlag.getTransactionValue(request.getSysFlag());
        switch (tranType) {
            case MessageSysFlag.TRANSACTION_NOT_TYPE: // 普通非事务消息
            case MessageSysFlag.TRANSACTION_COMMIT_TYPE: // 事务消息的最后提交类型
                DefaultMessageStore.this.putMessagePositionInfo(request);// 继续分发
                break;
            case MessageSysFlag.TRANSACTION_PREPARED_TYPE:// 事务消息的预提交
            case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE: // 回滚消息
                break;
        }
    }
}

又绕到 DefaultMessageStore 类了

public void putMessagePositionInfo(DispatchRequest dispatchRequest) {
    // 终于看到 ConsumeQueue（后面都简称 cq） 字样了，见名思意，就知道这跟消息队列有关了
    ConsumeQueue cq = this.findConsumeQueue(dispatchRequest.getTopic(), dispatchRequest.getQueueId());
    // 将分发消息存放到cq文件
    cq.putMessagePositionInfoWrapper(dispatchRequest);
}

public ConsumeQueue findConsumeQueue(String topic, int queueId) {
    // 先从缓存中根据 topic 获取，默认是没有的
    ConcurrentMap<Integer, ConsumeQueue> map = consumeQueueTable.get(topic);
    if (null == map) {
        // 创建一个Map，存放cq，Integer表示队列Id queueId
        ConcurrentMap<Integer, ConsumeQueue> newMap = new ConcurrentHashMap<Integer, ConsumeQueue>(128);
        // 先将newMap 根据topic存放到本地缓存的map中
        ConcurrentMap<Integer, ConsumeQueue> oldMap = consumeQueueTable.putIfAbsent(topic, newMap);
        if (oldMap != null) {
            map = oldMap;
        } else {
            map = newMap;
        }
    }
	// 取出 queueId 对应的cq，默认也是null
    ConsumeQueue logic = map.get(queueId);
    if (null == logic) {
        // 创建 cq对象
        ConsumeQueue newLogic = new ConsumeQueue(
            topic, // topic
            queueId, // 队列id
            StorePathConfigHelper.getStorePathConsumeQueue(this.messageStoreConfig.getStorePathRootDir()),// cq文件存放路径
            this.getMessageStoreConfig().getMapedFileSizeConsumeQueue(),// cq文件能存放的最大字节（300000 * 20），30w个元素，每个元素占20字节
            this);
        // put 进 map
        ConsumeQueue oldLogic = map.putIfAbsent(queueId, newLogic);
        if (oldLogic != null) {
            logic = oldLogic;
        } else {
            logic = newLogic;
        }
    }
	// 返回
    return logic;
}

再进入到 ConsumeQueue 类，执行分发的消息存入文件

public void putMessagePositionInfoWrapper(DispatchRequest request) {
    final int maxRetries = 30; // 最大重试次数
    // 是否可写标志
    boolean canWrite = this.defaultMessageStore.getRunningFlags().isCQWriteable();
    // 开始写入
    for (int i = 0; i < maxRetries && canWrite; i++) {
        long tagsCode = request.getTagsCode();
        // 对cq扩展的标志，默认为false，先忽略吧，以后有机会再单独拎出来讲
        if (isExtWriteEnable()) {
            ConsumeQueueExt.CqExtUnit cqExtUnit = new ConsumeQueueExt.CqExtUnit();
            cqExtUnit.setFilterBitMap(request.getBitMap());
            cqExtUnit.setMsgStoreTime(request.getStoreTimestamp());
            cqExtUnit.setTagsCode(request.getTagsCode());

            long extAddr = this.consumeQueueExt.put(cqExtUnit);
            if (isExtAddr(extAddr)) {
                tagsCode = extAddr;
            } else {
                log.warn("Save consume queue extend fail, So just save tagsCode! {}, topic:{}, queueId:{}, offset:{}", cqExtUnit,
                         topic, queueId, request.getCommitLogOffset());
            }
        }
        // 真正写文件的操作，四个参数分别告诉要从哪个偏移开始写，写多少，tags，写到cq的哪里
        boolean result = this.putMessagePositionInfo(request.getCommitLogOffset(),
                                                     request.getMsgSize(), tagsCode, request.getConsumeQueueOffset());
        if (result) {
            // 写入成功，记录时间
            this.defaultMessageStore.getStoreCheckpoint().setLogicsMsgTimestamp(request.getStoreTimestamp());
            return;
        } else {
            // XXX: warn and notify me
            log.warn("[BUG]put commit log position info to " + topic + ":" + queueId + " " + request.getCommitLogOffset()
                     + " failed, retry " + i + " times");

            try {
                // 失败了，过1秒再试下
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                log.warn("", e);
            }
        }
    }

    // XXX: warn and notify me
    log.error("[BUG]consume queue can not write, {} {}", this.topic, this.queueId);
    this.defaultMessageStore.getRunningFlags().makeLogicsQueueError();
}

private boolean putMessagePositionInfo(final long offset, final int size, final long tagsCode,
                                       final long cqOffset) {

    if (offset + size <= this.maxPhysicOffset) {
        log.warn("Maybe try to build consume queue repeatedly maxPhysicOffset={} phyOffset={}", maxPhysicOffset, offset);
        return true;
    }
	// 下面是对cq元素内容的存储，可以结合`章节第10章`的存储文件来阅读，会更轻松
    this.byteBufferIndex.flip();
    this.byteBufferIndex.limit(CQ_STORE_UNIT_SIZE); // 设置buffer最大20
    this.byteBufferIndex.putLong(offset); // commitlog 的偏移值
    this.byteBufferIndex.putInt(size); // 消息的大小
    this.byteBufferIndex.putLong(tagsCode); // 过滤tags的hash code值
	// cqOffset 表示在cq队列中的位置，每个元素 CQ_STORE_UNIT_SIZE 字节，这里就肯定要乘以 CQ_STORE_UNIT_SIZE
    final long expectLogicOffset = cqOffset * CQ_STORE_UNIT_SIZE;
	// 取出合适的cq文件，参考commitlog文件的获取
    MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile(expectLogicOffset);
    if (mappedFile != null) {
		// 判断是否初始创建cq，并且cqOffset不为0，但是cq文件可写的又是0，这种情况就表明cq不想从0开始写，那么前面就得补齐0
        if (mappedFile.isFirstCreateInQueue() && cqOffset != 0 && mappedFile.getWrotePosition() == 0) {
            this.minLogicOffset = expectLogicOffset;
            // 设置cq已经刷新的位置
            this.mappedFileQueue.setFlushedWhere(expectLogicOffset);
            // 设置cq已经提交完成的位置
            this.mappedFileQueue.setCommittedWhere(expectLogicOffset);
            // 将前面的补齐0
            this.fillPreBlank(mappedFile, expectLogicOffset);
            log.info("fill pre blank space " + mappedFile.getFileName() + " " + expectLogicOffset + " "
                     + mappedFile.getWrotePosition());
        }

        if (cqOffset != 0) {
            // 当前cq的可以开始写入偏移值
            long currentLogicOffset = mappedFile.getWrotePosition() + mappedFile.getFileFromOffset();
			// 当前期望写入的位置 不能小于 currentLogicOffset，否则非法
            if (expectLogicOffset < currentLogicOffset) {
                log.warn("Build  consume queue repeatedly, expectLogicOffset: {} currentLogicOffset: {} Topic: {} QID: {} Diff: {}",
                         expectLogicOffset, currentLogicOffset, this.topic, this.queueId, expectLogicOffset - currentLogicOffset);
                return true;
            }
			// 两者值不同，那就是有bug了，给予日志提醒
            if (expectLogicOffset != currentLogicOffset) {
                LOG_ERROR.warn(
                    "[BUG]logic queue order maybe wrong, expectLogicOffset: {} currentLogicOffset: {} Topic: {} QID: {} Diff: {}",
                    expectLogicOffset,
                    currentLogicOffset,
                    this.topic,
                    this.queueId,
                    expectLogicOffset - currentLogicOffset
                );
            }
        }
        // 记录分发后的commitlog的物理偏移
        this.maxPhysicOffset = offset + size;
        // 往cq文件中写入一个元素大小的数据
        return mappedFile.appendMessage(this.byteBufferIndex.array());
    }
    return false;
}

MappedFile.appendMessage

public boolean appendMessage(final byte[] data) {
    int currentPos = this.wrotePosition.get();
	// 当前位置+要写入数据的长度 不能大于 文件可容纳最大大小
    if ((currentPos + data.length) <= this.fileSize) {
        try {
            // 文件同步写入
            this.fileChannel.position(currentPos);
            this.fileChannel.write(ByteBuffer.wrap(data));
        } catch (Throwable e) {
            log.error("Error occurred when append message to mappedFile.", e);
        }
        // 增长写入的位置值
        this.wrotePosition.addAndGet(data.length);
        return true;
    }

    return false;
}

14.2 IndexFile存储

直接进 CommitLogDispatcherBuildIndex 类，这个类更简短，就几行代码

class CommitLogDispatcherBuildIndex implements CommitLogDispatcher {

    @Override
    public void dispatch(DispatchRequest request) {
        // 写入indexFile标志，默认开启的
        if (DefaultMessageStore.this.messageStoreConfig.isMessageIndexEnable()) {
            // 构建index，并写入
            DefaultMessageStore.this.indexService.buildIndex(request);
        }
    }
}

进入IndexService类

public void buildIndex(DispatchRequest req) {
    // 多次尝试获取或创建indexFile文件
    IndexFile indexFile = retryGetAndCreateIndexFile();
    if (indexFile != null) {
        long endPhyOffset = indexFile.getEndPhyOffset();
        DispatchRequest msg = req;
        String topic = msg.getTopic();
        String keys = msg.getKeys();
        // 检验：commitlog的提交偏移值，肯定不能写于上一次的最大偏移值，肯定是往大的写，不可能往小了写
        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;
        }
		// 该消息只有一个key
        if (req.getUniqKey() != null) {
            // 存入IndexFile
            indexFile = putKey(indexFile, msg, buildKey(topic, req.getUniqKey()));
            if (indexFile == null) {
                log.error("putKey error commitlog {} uniqkey {}", req.getCommitLogOffset(), req.getUniqKey());
                return;
            }
        }
		// 该消息有多个key
        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) {
                    // 存入IndexFile
                    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");
    }
}

多次尝试获取并创建IndexFile文件

public IndexFile retryGetAndCreateIndexFile() {
    IndexFile indexFile = null;
	// 遍历3次
    for (int times = 0; null == indexFile && times < MAX_TRY_IDX_CREATE; times++) {
        // 获取并创建文件
        indexFile = this.getAndCreateLastIndexFile();
        if (null != indexFile) // 取到了文件，直接退出for循环
            break;

        try {
            log.info("Tried to create index file " + times + " times");
            // 没有取到文件，等待1秒重试
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            log.error("Interrupted", e);
        }
    }

    if (null == indexFile) {// 最终还是失败，打印失败日志
        this.defaultMessageStore.getAccessRights().makeIndexFileError();
        log.error("Mark index file cannot build flag");
    }

    return indexFile;
}

public IndexFile getAndCreateLastIndexFile() {
    // 定义一些局部变量
    IndexFile indexFile = null;
    IndexFile prevIndexFile = null;
    long lastUpdateEndPhyOffset = 0;
    long lastUpdateIndexTimestamp = 0;

    {
        // 读锁
        this.readWriteLock.readLock().lock();
        // 缓存列表中有indexFile
        if (!this.indexFileList.isEmpty()) {
            // 取出最新的IndexFile
            IndexFile tmp = this.indexFileList.get(this.indexFileList.size() - 1);
            // 判断该文件是否已经写满了，通过 IndexCount 是否达到最大限度 5000000 * 4（500w个slot，每个slot占4字节）
            if (!tmp.isWriteFull()) {
                indexFile = tmp; // 没有写满，就继续用这个文件写
            } else {
                // 写满了，记录上次更新的物理偏移和时间戳
                lastUpdateEndPhyOffset = tmp.getEndPhyOffset();
                lastUpdateIndexTimestamp = tmp.getEndTimestamp();
                // 写满了，得用一个新文件了，所以当前文件tmp就是下一个文件的前一个文件了，哈哈，有点绕
                prevIndexFile = tmp;
            }
        }
		// 读锁释放
        this.readWriteLock.readLock().unlock();
    }
	// 初次创建
    if (indexFile == null) {
        try {
            // IndexFile文件命名是用当前时间戳转换成人类可读的年月日时分秒这种格式
            String fileName =
                this.storePath + File.separator
                + UtilAll.timeMillisToHumanString(System.currentTimeMillis());
            indexFile =
                new IndexFile(fileName, this.hashSlotNum, this.indexNum, lastUpdateEndPhyOffset,
                              lastUpdateIndexTimestamp);
            this.readWriteLock.writeLock().lock(); // 写锁
            this.indexFileList.add(indexFile); // 添加到缓存列表
        } catch (Exception e) {
            log.error("getLastIndexFile exception ", e);
        } finally {
            this.readWriteLock.writeLock().unlock(); // 释放写锁
        }

        if (indexFile != null) {
            // 写新的文件之前要把上一个文件的内存从缓冲区强制刷新到磁盘
            final IndexFile flushThisFile = prevIndexFile;
            Thread flushThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    // 通过线程强制刷新上一个文件的内容到磁盘
                    IndexService.this.flush(flushThisFile);
                }
            }, "FlushIndexFileThread");
			// 将刷新线程设置成后台线程
            flushThread.setDaemon(true);
            // 启动刷新线程
            flushThread.start();
        }
    }

    return indexFile;
}

存入IndexFile

private IndexFile putKey(IndexFile indexFile, DispatchRequest msg, String idxKey) {
    // 持续遍历写入IndexFile
    for (boolean ok = indexFile.putKey(idxKey, msg.getCommitLogOffset(), msg.getStoreTimestamp()); !ok; ) {
        log.warn("Index file [" + indexFile.getFileName() + "] is full, trying to create another one");

        indexFile = retryGetAndCreateIndexFile();
        if (null == indexFile) {
            return null;
        }

        ok = indexFile.putKey(idxKey, msg.getCommitLogOffset(), msg.getStoreTimestamp());
    }

    return indexFile;
}

// 这个方法最好结合`第十章-存储文件`来看，内部就是对IndexHeader、Slot、Indexes的存储，理解了`图10-1`，这个方法的代码就不用看了
public boolean putKey(final String key, final long phyOffset, final long storeTimestamp) {
    if (this.indexHeader.getIndexCount() < this.indexNum) {
        // key的hash值
        int keyHash = indexKeyHashMethod(key);
        // 求模得出slot的槽位
        int slotPos = keyHash % this.hashSlotNum;
        // IndexHeader的大小（40字节）+槽位*每个槽位所占大小（4字节），得出要写入数据的槽位偏移
        int absSlotPos = IndexHeader.INDEX_HEADER_SIZE + slotPos * hashSlotSize;

        FileLock fileLock = null;

        try {

            // 先看看该槽位，原先有没有值
            int slotValue = this.mappedByteBuffer.getInt(absSlotPos);
            // 检验slotValue的合法性
            if (slotValue <= invalidIndex || slotValue > this.indexHeader.getIndexCount()) {
                slotValue = invalidIndex;
            }
			// 求出当前存储的时间与IndexFile存入的第一个消息的时间戳的比较
            long timeDiff = storeTimestamp - this.indexHeader.getBeginTimestamp();

            timeDiff = timeDiff / 1000;
			// 修正 timeDiff 的值
            if (this.indexHeader.getBeginTimestamp() <= 0) {
                timeDiff = 0;
            } else if (timeDiff > Integer.MAX_VALUE) {
                timeDiff = Integer.MAX_VALUE;
            } else if (timeDiff < 0) {
                timeDiff = 0;
            }
			// 计算开始写Index的位置
            int absIndexPos =
                IndexHeader.INDEX_HEADER_SIZE  // IndexHeader 头部所占空间
                + this.hashSlotNum * hashSlotSize // 500w个slot所占空间
                + this.indexHeader.getIndexCount() * indexSize; // IndexCount表示已经占用的数量
			// 存入keyhash
            this.mappedByteBuffer.putInt(absIndexPos, keyHash);
            // 存入commitlog物理偏移
            this.mappedByteBuffer.putLong(absIndexPos + 4, phyOffset);
            // 存入时差
            this.mappedByteBuffer.putInt(absIndexPos + 4 + 8, (int) timeDiff);
            // 同一个slot下的前一个index的索引值，为解决slot槽位冲突，可以理解成HashMap中hashcode冲突时的链表
            this.mappedByteBuffer.putInt(absIndexPos + 4 + 8 + 4, slotValue);
			// 往slot中存入当前存放index的索引值
            this.mappedByteBuffer.putInt(absSlotPos, this.indexHeader.getIndexCount());
			// 初次存入，设置一下第一个元素时间戳和commitlog物理偏移
            if (this.indexHeader.getIndexCount() <= 1) {
                this.indexHeader.setBeginPhyOffset(phyOffset);
                this.indexHeader.setBeginTimestamp(storeTimestamp);
            }
			// 统计
            this.indexHeader.incHashSlotCount();
            this.indexHeader.incIndexCount();
            // 设置一下最后一个元素的时间戳和commitlog物理偏移
            this.indexHeader.setEndPhyOffset(phyOffset);
            this.indexHeader.setEndTimestamp(storeTimestamp);
			// 结束，返回true
            return true;
        } catch (Exception e) {
            log.error("putKey exception, Key: " + key + " KeyHashCode: " + key.hashCode(), e);
        } finally {
            if (fileLock != null) {
                try {
                    fileLock.release();
                } catch (IOException e) {
                    log.error("Failed to release the lock", e);
                }
            }
        }
    } else {
        log.warn("Over index file capacity: index count = " + this.indexHeader.getIndexCount()
                 + "; index max num = " + this.indexNum);
    }

    return false;
}