RocketMq 源码解读-Broker（1）

这边源码分支为release-4.2.0

处理拉取信息请求

通过broker模块下面的processor目录下, 我们找到org.apache.rocketmq.broker.processor.PullMessageProcessor这个类的processRequest方法.这边就不省略代码了, 只是在重要的部分加上注释, 供参阅

private RemotingCommand processRequest(final Channel channel, RemotingCommand request, boolean brokerAllowSuspend)
        throws RemotingCommandException {
        RemotingCommand response = RemotingCommand.createResponseCommand(PullMessageResponseHeader.class);
        final PullMessageResponseHeader responseHeader = (PullMessageResponseHeader) response.readCustomHeader();
        final PullMessageRequestHeader requestHeader =
            (PullMessageRequestHeader) request.decodeCommandCustomHeader(PullMessageRequestHeader.class);

        response.setOpaque(request.getOpaque());

        log.debug("receive PullMessage request command, {}", request);
        // 从配置检查broker是否允许读取
        if (!PermName.isReadable(this.brokerController.getBrokerConfig().getBrokerPermission())) {
            response.setCode(ResponseCode.NO_PERMISSION);
            response.setRemark(String.format("the broker[%s] pulling message is forbidden", this.brokerController.getBrokerConfig().getBrokerIP1()));
            return response;
        }

        // 检查订阅组数据，是否允许消费
        SubscriptionGroupConfig subscriptionGroupConfig =
            this.brokerController.getSubscriptionGroupManager().findSubscriptionGroupConfig(requestHeader.getConsumerGroup());
        if (null == subscriptionGroupConfig) {
            response.setCode(ResponseCode.SUBSCRIPTION_GROUP_NOT_EXIST);
            response.setRemark(String.format("subscription group [%s] does not exist, %s", requestHeader.getConsumerGroup(), FAQUrl.suggestTodo(FAQUrl.SUBSCRIPTION_GROUP_NOT_EXIST)));
            return response;
        }

        if (!subscriptionGroupConfig.isConsumeEnable()) {
            response.setCode(ResponseCode.NO_PERMISSION);
            response.setRemark("subscription group no permission, " + requestHeader.getConsumerGroup());
            return response;
        }

        // 从请求头的配置中, 检查一些数据.
        final boolean hasSuspendFlag = PullSysFlag.hasSuspendFlag(requestHeader.getSysFlag());
        final boolean hasCommitOffsetFlag = PullSysFlag.hasCommitOffsetFlag(requestHeader.getSysFlag());
        final boolean hasSubscriptionFlag = PullSysFlag.hasSubscriptionFlag(requestHeader.getSysFlag());

        final long suspendTimeoutMillisLong = hasSuspendFlag ? requestHeader.getSuspendTimeoutMillis() : 0;

        TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
        if (null == topicConfig) {
            log.error("the topic {} not exist, consumer: {}", requestHeader.getTopic(), RemotingHelper.parseChannelRemoteAddr(channel));
            response.setCode(ResponseCode.TOPIC_NOT_EXIST);
            response.setRemark(String.format("topic[%s] not exist, apply first please! %s", requestHeader.getTopic(), FAQUrl.suggestTodo(FAQUrl.APPLY_TOPIC_URL)));
            return response;
        }

        if (!PermName.isReadable(topicConfig.getPerm())) {
            response.setCode(ResponseCode.NO_PERMISSION);
            response.setRemark("the topic[" + requestHeader.getTopic() + "] pulling message is forbidden");
            return response;
        }

        if (requestHeader.getQueueId() < 0 || requestHeader.getQueueId() >= topicConfig.getReadQueueNums()) {
            String errorInfo = String.format("queueId[%d] is illegal, topic:[%s] topicConfig.readQueueNums:[%d] consumer:[%s]",
                requestHeader.getQueueId(), requestHeader.getTopic(), topicConfig.getReadQueueNums(), channel.remoteAddress());
            log.warn(errorInfo);
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark(errorInfo);
            return response;
        }

        SubscriptionData subscriptionData = null;
        ConsumerFilterData consumerFilterData = null;
        if (hasSubscriptionFlag) {
            try {
                subscriptionData = FilterAPI.build(
                    requestHeader.getTopic(), requestHeader.getSubscription(), requestHeader.getExpressionType()
                );
                if (!ExpressionType.isTagType(subscriptionData.getExpressionType())) {
                    consumerFilterData = ConsumerFilterManager.build(
                        requestHeader.getTopic(), requestHeader.getConsumerGroup(), requestHeader.getSubscription(),
                        requestHeader.getExpressionType(), requestHeader.getSubVersion()
                    );
                    assert consumerFilterData != null;
                }
            } catch (Exception e) {
                log.warn("Parse the consumer's subscription[{}] failed, group: {}", requestHeader.getSubscription(),
                    requestHeader.getConsumerGroup());
                response.setCode(ResponseCode.SUBSCRIPTION_PARSE_FAILED);
                response.setRemark("parse the consumer's subscription failed");
                return response;
            }
        } else {
            ConsumerGroupInfo consumerGroupInfo =
                this.brokerController.getConsumerManager().getConsumerGroupInfo(requestHeader.getConsumerGroup());
            if (null == consumerGroupInfo) {
                log.warn("the consumer's group info not exist, group: {}", requestHeader.getConsumerGroup());
                response.setCode(ResponseCode.SUBSCRIPTION_NOT_EXIST);
                response.setRemark("the consumer's group info not exist" + FAQUrl.suggestTodo(FAQUrl.SAME_GROUP_DIFFERENT_TOPIC));
                return response;
            }

            if (!subscriptionGroupConfig.isConsumeBroadcastEnable()
                && consumerGroupInfo.getMessageModel() == MessageModel.BROADCASTING) {
                response.setCode(ResponseCode.NO_PERMISSION);
                response.setRemark("the consumer group[" + requestHeader.getConsumerGroup() + "] can not consume by broadcast way");
                return response;
            }

            subscriptionData = consumerGroupInfo.findSubscriptionData(requestHeader.getTopic());
            if (null == subscriptionData) {
                log.warn("the consumer's subscription not exist, group: {}, topic:{}", requestHeader.getConsumerGroup(), requestHeader.getTopic());
                response.setCode(ResponseCode.SUBSCRIPTION_NOT_EXIST);
                response.setRemark("the consumer's subscription not exist" + FAQUrl.suggestTodo(FAQUrl.SAME_GROUP_DIFFERENT_TOPIC));
                return response;
            }

            if (subscriptionData.getSubVersion() < requestHeader.getSubVersion()) {
                log.warn("The broker's subscription is not latest, group: {} {}", requestHeader.getConsumerGroup(),
                    subscriptionData.getSubString());
                response.setCode(ResponseCode.SUBSCRIPTION_NOT_LATEST);
                response.setRemark("the consumer's subscription not latest");
                return response;
            }
            if (!ExpressionType.isTagType(subscriptionData.getExpressionType())) {
                consumerFilterData = this.brokerController.getConsumerFilterManager().get(requestHeader.getTopic(),
                    requestHeader.getConsumerGroup());
                if (consumerFilterData == null) {
                    response.setCode(ResponseCode.FILTER_DATA_NOT_EXIST);
                    response.setRemark("The broker's consumer filter data is not exist!Your expression may be wrong!");
                    return response;
                }
                if (consumerFilterData.getClientVersion() < requestHeader.getSubVersion()) {
                    log.warn("The broker's consumer filter data is not latest, group: {}, topic: {}, serverV: {}, clientV: {}",
                        requestHeader.getConsumerGroup(), requestHeader.getTopic(), consumerFilterData.getClientVersion(), requestHeader.getSubVersion());
                    response.setCode(ResponseCode.FILTER_DATA_NOT_LATEST);
                    response.setRemark("the consumer's consumer filter data not latest");
                    return response;
                }
            }
        }

        if (!ExpressionType.isTagType(subscriptionData.getExpressionType())
            && !this.brokerController.getBrokerConfig().isEnablePropertyFilter()) {
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark("The broker does not support consumer to filter message by " + subscriptionData.getExpressionType());
            return response;
        }

        MessageFilter messageFilter;
        if (this.brokerController.getBrokerConfig().isFilterSupportRetry()) {
            messageFilter = new ExpressionForRetryMessageFilter(subscriptionData, consumerFilterData,
                this.brokerController.getConsumerFilterManager());
        } else {
            messageFilter = new ExpressionMessageFilter(subscriptionData, consumerFilterData,
                this.brokerController.getConsumerFilterManager());
        }
        
		//********************* 以上都是检查, 和参数组装. *********************
		
        // getMessage(获取消息结果) 疑问:1. messageFilter来自哪里? 难道不是client配置?
        final GetMessageResult getMessageResult =
            this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
                requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), messageFilter);
        // 如果获取到消息, 开始判断返回逻辑 以及参数组装
        if (getMessageResult != null) {
            response.setRemark(getMessageResult.getStatus().name());
            responseHeader.setNextBeginOffset(getMessageResult.getNextBeginOffset());
            responseHeader.setMinOffset(getMessageResult.getMinOffset());
            responseHeader.setMaxOffset(getMessageResult.getMaxOffset());

            if (getMessageResult.isSuggestPullingFromSlave()) {
                responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getWhichBrokerWhenConsumeSlowly());
            } else {
                responseHeader.setSuggestWhichBrokerId(MixAll.MASTER_ID);
            }

            switch (this.brokerController.getMessageStoreConfig().getBrokerRole()) {
                case ASYNC_MASTER:
                case SYNC_MASTER:
                    break;
                case SLAVE:
                    if (!this.brokerController.getBrokerConfig().isSlaveReadEnable()) {
                        response.setCode(ResponseCode.PULL_RETRY_IMMEDIATELY);
                        responseHeader.setSuggestWhichBrokerId(MixAll.MASTER_ID);
                    }
                    break;
            }

            if (this.brokerController.getBrokerConfig().isSlaveReadEnable()) {
                // consume too slow ,redirect to another machine
                if (getMessageResult.isSuggestPullingFromSlave()) {
                    responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getWhichBrokerWhenConsumeSlowly());
                }
                // consume ok
                else {
                    responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getBrokerId());
                }
            } else {
                responseHeader.setSuggestWhichBrokerId(MixAll.MASTER_ID);
            }
            // 判断结果的各种状态
            switch (getMessageResult.getStatus()) {
                case FOUND:
                    response.setCode(ResponseCode.SUCCESS);
                    break;
                case MESSAGE_WAS_REMOVING:
                    response.setCode(ResponseCode.PULL_RETRY_IMMEDIATELY);
                    break;
                case NO_MATCHED_LOGIC_QUEUE:
                case NO_MESSAGE_IN_QUEUE:
                    if (0 != requestHeader.getQueueOffset()) {
                        response.setCode(ResponseCode.PULL_OFFSET_MOVED);

                        // XXX: warn and notify me
                        log.info("the broker store no queue data, fix the request offset {} to {}, Topic: {} QueueId: {} Consumer Group: {}",
                            requestHeader.getQueueOffset(),
                            getMessageResult.getNextBeginOffset(),
                            requestHeader.getTopic(),
                            requestHeader.getQueueId(),
                            requestHeader.getConsumerGroup()
                        );
                    } else {
                        response.setCode(ResponseCode.PULL_NOT_FOUND);
                    }
                    break;
                case NO_MATCHED_MESSAGE:
                    response.setCode(ResponseCode.PULL_RETRY_IMMEDIATELY);
                    break;
                case OFFSET_FOUND_NULL:
                    response.setCode(ResponseCode.PULL_NOT_FOUND);
                    break;
                case OFFSET_OVERFLOW_BADLY:
                    response.setCode(ResponseCode.PULL_OFFSET_MOVED);
                    // XXX: warn and notify me
                    log.info("the request offset: {} over flow badly, broker max offset: {}, consumer: {}",
                        requestHeader.getQueueOffset(), getMessageResult.getMaxOffset(), channel.remoteAddress());
                    break;
                case OFFSET_OVERFLOW_ONE:
                    response.setCode(ResponseCode.PULL_NOT_FOUND);
                    break;
                case OFFSET_TOO_SMALL:
                    response.setCode(ResponseCode.PULL_OFFSET_MOVED);
                    log.info("the request offset too small. group={}, topic={}, requestOffset={}, brokerMinOffset={}, clientIp={}",
                        requestHeader.getConsumerGroup(), requestHeader.getTopic(), requestHeader.getQueueOffset(),
                        getMessageResult.getMinOffset(), channel.remoteAddress());
                    break;
                default:
                    assert false;
                    break;
            }
			
			// 检查是否还有需要触发回调的钩子函数
            if (this.hasConsumeMessageHook()) {
                ConsumeMessageContext context = new ConsumeMessageContext();
                context.setConsumerGroup(requestHeader.getConsumerGroup());
                context.setTopic(requestHeader.getTopic());
                context.setQueueId(requestHeader.getQueueId());

                String owner = request.getExtFields().get(BrokerStatsManager.COMMERCIAL_OWNER);

                switch (response.getCode()) {
                    case ResponseCode.SUCCESS:
                        int commercialBaseCount = brokerController.getBrokerConfig().getCommercialBaseCount();
                        int incValue = getMessageResult.getMsgCount4Commercial() * commercialBaseCount;

                        context.setCommercialRcvStats(BrokerStatsManager.StatsType.RCV_SUCCESS);
                        context.setCommercialRcvTimes(incValue);
                        context.setCommercialRcvSize(getMessageResult.getBufferTotalSize());
                        context.setCommercialOwner(owner);

                        break;
                    case ResponseCode.PULL_NOT_FOUND:
                        if (!brokerAllowSuspend) {

                            context.setCommercialRcvStats(BrokerStatsManager.StatsType.RCV_EPOLLS);
                            context.setCommercialRcvTimes(1);
                            context.setCommercialOwner(owner);

                        }
                        break;
                    case ResponseCode.PULL_RETRY_IMMEDIATELY:
                    case ResponseCode.PULL_OFFSET_MOVED:
                        context.setCommercialRcvStats(BrokerStatsManager.StatsType.RCV_EPOLLS);
                        context.setCommercialRcvTimes(1);
                        context.setCommercialOwner(owner);
                        break;
                    default:
                        assert false;
                        break;
                }

                this.executeConsumeMessageHookBefore(context);
            }

            switch (response.getCode()) {
                case ResponseCode.SUCCESS:

                    this.brokerController.getBrokerStatsManager().incGroupGetNums(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
                        getMessageResult.getMessageCount());

                    this.brokerController.getBrokerStatsManager().incGroupGetSize(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
                        getMessageResult.getBufferTotalSize());

                    this.brokerController.getBrokerStatsManager().incBrokerGetNums(getMessageResult.getMessageCount());
                    if (this.brokerController.getBrokerConfig().isTransferMsgByHeap()) {
                        final long beginTimeMills = this.brokerController.getMessageStore().now();
                        final byte[] r = this.readGetMessageResult(getMessageResult, requestHeader.getConsumerGroup(), requestHeader.getTopic(), requestHeader.getQueueId());
                        this.brokerController.getBrokerStatsManager().incGroupGetLatency(requestHeader.getConsumerGroup(),
                            requestHeader.getTopic(), requestHeader.getQueueId(),
                            (int) (this.brokerController.getMessageStore().now() - beginTimeMills));
                        response.setBody(r);
                    } else {
                        try {
                            // ************************ 通过netty 将结果发送回去 ************************
                            FileRegion fileRegion =
                                new ManyMessageTransfer(response.encodeHeader(getMessageResult.getBufferTotalSize()), getMessageResult);
                            channel.writeAndFlush(fileRegion).addListener(new ChannelFutureListener() {
                                @Override
                                public void operationComplete(ChannelFuture future) throws Exception {
                                    getMessageResult.release();
                                    if (!future.isSuccess()) {
                                        log.error("transfer many message by pagecache failed, {}", channel.remoteAddress(), future.cause());
                                    }
                                }
                            });
                        } catch (Throwable e) {
                            log.error("transfer many message by pagecache exception", e);
                            getMessageResult.release();
                        }

                        response = null;
                    }
                    break;
                case ResponseCode.PULL_NOT_FOUND:

                    if (brokerAllowSuspend && hasSuspendFlag) {
                        long pollingTimeMills = suspendTimeoutMillisLong;
                        if (!this.brokerController.getBrokerConfig().isLongPollingEnable()) {
                            pollingTimeMills = this.brokerController.getBrokerConfig().getShortPollingTimeMills();
                        }

                        String topic = requestHeader.getTopic();
                        long offset = requestHeader.getQueueOffset();
                        int queueId = requestHeader.getQueueId();
                        PullRequest pullRequest = new PullRequest(request, channel, pollingTimeMills,
                            this.brokerController.getMessageStore().now(), offset, subscriptionData, messageFilter);
                        this.brokerController.getPullRequestHoldService().suspendPullRequest(topic, queueId, pullRequest);
                        response = null;
                        break;
                    }

                case ResponseCode.PULL_RETRY_IMMEDIATELY:
                    break;
                case ResponseCode.PULL_OFFSET_MOVED:
                    if (this.brokerController.getMessageStoreConfig().getBrokerRole() != BrokerRole.SLAVE
                        || this.brokerController.getMessageStoreConfig().isOffsetCheckInSlave()) {
                        MessageQueue mq = new MessageQueue();
                        mq.setTopic(requestHeader.getTopic());
                        mq.setQueueId(requestHeader.getQueueId());
                        mq.setBrokerName(this.brokerController.getBrokerConfig().getBrokerName());

                        OffsetMovedEvent event = new OffsetMovedEvent();
                        event.setConsumerGroup(requestHeader.getConsumerGroup());
                        event.setMessageQueue(mq);
                        event.setOffsetRequest(requestHeader.getQueueOffset());
                        event.setOffsetNew(getMessageResult.getNextBeginOffset());
                        this.generateOffsetMovedEvent(event);
                        log.warn(
                            "PULL_OFFSET_MOVED:correction offset. topic={}, groupId={}, requestOffset={}, newOffset={}, suggestBrokerId={}",
                            requestHeader.getTopic(), requestHeader.getConsumerGroup(), event.getOffsetRequest(), event.getOffsetNew(),
                            responseHeader.getSuggestWhichBrokerId());
                    } else {
                        responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getBrokerId());
                        response.setCode(ResponseCode.PULL_RETRY_IMMEDIATELY);
                        log.warn("PULL_OFFSET_MOVED:none correction. topic={}, groupId={}, requestOffset={}, suggestBrokerId={}",
                            requestHeader.getTopic(), requestHeader.getConsumerGroup(), requestHeader.getQueueOffset(),
                            responseHeader.getSuggestWhichBrokerId());
                    }

                    break;
                default:
                    assert false;
            }
        } else {
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark("store getMessage return null");
        }

        boolean storeOffsetEnable = brokerAllowSuspend;
        storeOffsetEnable = storeOffsetEnable && hasCommitOffsetFlag;
        storeOffsetEnable = storeOffsetEnable
            && this.brokerController.getMessageStoreConfig().getBrokerRole() != BrokerRole.SLAVE;
           // ********************* broker 也会保存一份各个topic的offset情况,猜测会在主从同步时候用到 *********************
         
        if (storeOffsetEnable) {
            this.brokerController.getConsumerOffsetManager().commitOffset(RemotingHelper.parseChannelRemoteAddr(channel),
                requestHeader.getConsumerGroup(), requestHeader.getTopic(), requestHeader.getQueueId(), requestHeader.getCommitOffset());
        }
        return response;
    }

其中， 有一行代码为

final GetMessageResult getMessageResult =
            this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
                requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), messageFilter);

找到getMessage的实现类package org.apache.rocketmq.store.DefaultMessageStore的getMessage方法, 当中有一大部分代码是检查传入的offset是否合法.
重要的代码是SelectMappedBufferResult selectResult = this.commitLog.getMessage(offsetPy, sizePy);
再通过package org.apache.rocketmq.store.CommitLog类,来找到getMessage方法.

public SelectMappedBufferResult getMessage(final long offset, final int size) {
    int mappedFileSize = this.defaultMessageStore.getMessageStoreConfig().getMapedFileSizeCommitLog();
    MappedFile mappedFile = this.mappedFileQueue.findMappedFileByOffset(offset, offset == 0);
    if (mappedFile != null) {
        int pos = (int) (offset % mappedFileSize);
// 从MappedFile中读取mapper,这个类就是底层存储消息的文件的映射对象了.
        return mappedFile.selectMappedBuffer(pos, size);
    }
    return null;
}

再来看最终的文件映射类org.apache.rocketmq.store.MappedFile, 这边用到了NIO的内存映射

public SelectMappedBufferResult selectMappedBuffer(int pos, int size) {
    int readPosition = getReadPosition();
    if ((pos + size) <= readPosition) {

        if (this.hold()) {
            // 从mappedByteBuffer中复制一个新的bytebuffer.进行数据截取操作, 并将内容返回
            ByteBuffer byteBuffer = this.mappedByteBuffer.slice();
            byteBuffer.position(pos);
            ByteBuffer byteBufferNew = byteBuffer.slice();
            byteBufferNew.limit(size);
            return new SelectMappedBufferResult(this.fileFromOffset + pos, byteBufferNew, size, this);
        } else {
            log.warn("matched, but hold failed, request pos: " + pos + ", fileFromOffset: "
                + this.fileFromOffset);
        }
    } else {
        log.warn("selectMappedBuffer request pos invalid, request pos: " + pos + ", size: " + size
            + ", fileFromOffset: " + this.fileFromOffset);
    }

    return null;
}

至此, 我们就算知道broker如何从文件系统中读取内容了.

这边还有个疑问, 如何更新已经被获取到的offerSet呢? 是不是由client自己保管,自己更新读取到哪里了?

为了解决这个疑问, 我们往上翻翻代码, 看在org.apache.rocketmq.broker.processor.PullMessageProcessor这个类中getMessage(startOffset,size) 这边的startOffset最终是怎么传入的.

final GetMessageResult getMessageResult =
   this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
       requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), messageFilter);

可以看到requestHeader.getQueueOffset() 是从请求头去获取的offset, 所以确实由客户端自己维护的.