RocketMQ的前提回顧
RocketMQ是一款分散式、佇列模型的訊息中介軟體，具有以下特點：
- 能夠保證嚴格的訊息順序
- 提供豐富的訊息拉取模式
- 高效的訂閱者水平擴充套件能力
- 實時的訊息訂閱機制
- 億級訊息堆積能力
為什麼使用RocketMQ
- 強調叢集無單點，可擴充套件，任意一點高可用、水平可擴充套件
- 海量訊息堆積能力，訊息堆積後寫入低延遲
- 支援上萬個佇列
- 訊息失敗重試機制
- 訊息可查詢
- 開源社群活躍
- 成熟度已經經過淘寶雙十一的考驗
RocketMQ的發展變化
RocketMQ開源是使用檔案作為持久化工具，阿里內部未開源的效能會更高，使用oceanBase作為持久化工具。
在RocketMQ1.x和2.x使用zookeeper管理叢集，3.x開始使用nameserver代替zk，更輕量級，此外RocketMQ的客戶端擁有兩種的操作方式：DefaultMQPushConsumer和DefaultMQPullConsumer。
DefaultMQPushConsumer的Maven配置
<dependency>
<groupId>org.apache.rocketmq</groupId>
<artifactId>rocketmq-client</artifactId>
<version>4.3.0</version>
</dependency>
DefaultMQPushConsumer使用示例
- CONSUME_FROM_LAST_OFFSET：第一次啟動從佇列最後位置消費，後續再啟動接著上次消費的進度開始消費
- CONSUME_FROM_FIRST_OFFSET：第一次啟動從佇列初始位置消費，後續再啟動接著上次消費的進度開始消費
- CONSUME_FROM_TIMESTAMP：第一次啟動從指定時間點位置消費，後續再啟動接著上次消費的進度開始消費
以上所說的第一次啟動是指從來沒有消費過的消費者，如果該消費者消費過，那麼會在broker端記錄該消費者的消費位置，如果該消費者掛了再啟動，那麼自動從上次消費的進度開始
public class MQPushConsumer {
public static void main(String[] args) throws MQClientException {
String groupName = "rocketMqGroup1";
// 用於把多個Consumer組織到一起，提高併發處理能力
DefaultMQPushConsumer consumer = new DefaultMQPushConsumer(groupName);
// 設定nameServer地址，多個以;分隔
consumer.setNamesrvAddr("name-serverl-ip:9876;name-server2-ip:9876"); consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);
consumer.setMessageModel(MessageModel.BROADCASTING);
// 訂閱topic，可以對指定訊息進行過濾，例如："TopicTest","tagl||tag2||tag3",*或null表示topic所有訊息
consumer.subscribe("order-topic", "*");
consumer.registerMessageListener(new MessageListenerConcurrently() {
@Override
public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> mgs,
ConsumeConcurrentlyContext consumeconcurrentlycontext) {
System.out.println(Thread.currentThread().getName()+"Receive New Messages:"+mgs);
return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
}
});
consumer.start();
}
}
- CLUSTERING：預設模式，同一個ConsumerGroup(groupName相同)每個consumer只消費所訂閱訊息的一部分內容，同一個ConsumerGroup裡所有的Consumer訊息加起來才是所
- 訂閱topic整體，從而達到負載均衡的目的
- BROADCASTING：同一個ConsumerGroup每個consumer都消費到所訂閱topic所有訊息，也就是一個消費會被多次分發，被多個consumer消費。
ConsumeConcurrentlyStatus.RECONSUME_LATER boker會根據設定的messageDelayLevel發起重試，預設16次。
DefaultMQPushConsumerImpl中各個物件的主要功能如下：
RebalancePushImpl：主要負責決定，當前的consumer應該從哪些Queue中消費訊息；
- 1）PullAPIWrapper：長連線，負責從broker處拉取訊息，然後利用ConsumeMessageService回撥使用者的Listener執行訊息消費邏輯；
- 2）ConsumeMessageService：實現所謂的"Push-被動"消費機制；從Broker拉取的訊息後，封裝成ConsumeRequest提交給ConsumeMessageSerivce，此service負責回撥使用者的Listener消費訊息；
- 3）OffsetStore：維護當前consumer的消費記錄（offset）；有兩種實現，Local和Rmote，Local儲存在本地磁碟上，適用於BROADCASTING廣播消費模式；而Remote則將消費進度儲存在Broker上，適用於CLUSTERING叢集消費模式；
- 4）MQClientFactory：負責管理client（consumer、producer），並提供多中功能介面供各個Service（Rebalance、PullMessage等）呼叫；大部分邏輯均在這個類中完成；
consumer.registerMessageListener執行過程：
/**
* Register a callback to execute on message arrival for concurrent consuming.
* @param messageListener message handling callback.
*/
@Override
public void registerMessageListener(MessageListenerConcurrently messageListener) {
this.messageListener = messageListener; this.defaultMQPushConsumerImpl.registerMessageListener(messageListener);
}
通過原始碼可以看出主要實現過程在DefaultMQPushConsumerImpl類中consumer.start後呼叫DefaultMQPushConsumerImpl的同步start方法
public synchronized void start() throws MQClientException {
switch (this.serviceState) {
case CREATE_JUST:
log.info("the consumer [{}] start beginning. messageModel={}, isUnitMode={}", this.defaultMQPushConsumer.getConsumerGroup(),
this.defaultMQPushConsumer.getMessageModel(), this.defaultMQPushConsumer.isUnitMode());
this.serviceState = ServiceState.START_FAILED;
this.checkConfig();
this.copySubscription();
if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {
this.defaultMQPushConsumer.changeInstanceNameToPID();
}
this.mQClientFactory = MQClientManager.getInstance().getAndCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);
this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());
this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());
this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());
this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);
this.pullAPIWrapper = new PullAPIWrapper(
mQClientFactory,
this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);
if (this.defaultMQPushConsumer.getOffsetStore() != null) {
this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();
} else {
switch (this.defaultMQPushConsumer.getMessageModel()) {
case BROADCASTING:
this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
break;
case CLUSTERING:
this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
break;
default:
break;
}
this.defaultMQPushConsumer.setOffsetStore(this.offsetStore);
}
this.offsetStore.load();
if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {
this.consumeOrderly = true;
this.consumeMessageService =
new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());
} else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {
this.consumeOrderly = false;
this.consumeMessageService =
new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());
}
this.consumeMessageService.start();
boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
if (!registerOK) {
this.serviceState = ServiceState.CREATE_JUST;
this.consumeMessageService.shutdown();
throw new MQClientException("The consumer group[" + this.defaultMQPushConsumer.getConsumerGroup()
+ "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),
null);
}
mQClientFactory.start();
log.info("the consumer [{}] start OK.", this.defaultMQPushConsumer.getConsumerGroup());
this.serviceState = ServiceState.RUNNING;
break;
case RUNNING:
case START_FAILED:
case SHUTDOWN_ALREADY:
throw new MQClientException("The PushConsumer service state not OK, maybe started once, "
+ this.serviceState
+ FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),
null);
default:
break;
}
this.updateTopicSubscribeInfoWhenSubscriptionChanged();
this.mQClientFactory.checkClientInBroker();
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
this.mQClientFactory.rebalanceImmediately();
}
通過mQClientFactory.start();發我們發現他呼叫
public void start() throws MQClientException {
synchronized (this) {
switch (this.serviceState) {
case CREATE_JUST:
this.serviceState = ServiceState.START_FAILED;
// If not specified,looking address from name server
if (null == this.clientConfig.getNamesrvAddr()) {
this.mQClientAPIImpl.fetchNameServerAddr();
}
// Start request-response channel
this.mQClientAPIImpl.start();
// Start various schedule tasks
this.startScheduledTask();
// Start pull service
this.pullMessageService.start();
// Start rebalance service
this.rebalanceService.start();
// Start push service
this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
log.info("the client factory [{}] start OK", this.clientId);
this.serviceState = ServiceState.RUNNING;
break;
case RUNNING:
break;
case SHUTDOWN_ALREADY:
break;
case START_FAILED:
throw new MQClientException("The Factory object[" + this.getClientId() + "] has been created before, and failed.", null);
default:
break;
}
}
}
在這個方法中有多個start，我們主要看pullMessageService.start();通過這裡我們發現RocketMQ的Push模式底層其實也是通過pull實現的，下面我們來看下pullMessageService處理了哪些邏輯：
private void pullMessage(final PullRequest pullRequest) {
final MQConsumerInner consumer = this.mQClientFactory.selectConsumer(pullRequest.getConsumerGroup());
if (consumer != null) {
DefaultMQPushConsumerImpl impl = (DefaultMQPushConsumerImpl) consumer;
impl.pullMessage(pullRequest);
} else {
log.warn("No matched consumer for the PullRequest {}, drop it", pullRequest);
}
}
我們發現其實他還是通過DefaultMQPushConsumerImpl類的pullMessage方法來進行訊息的邏輯處理.
pullRequest拉取方式
PullRequest這裡說明一下，上面我們已經提了一下rocketmq的push模式其實是通過pull模式封裝實現的，pullrequest這裡是通過長輪詢的方式達到push效果。
長輪詢方式既有pull的優點又有push模式的實時性有點。
-
push方式是server端接收到訊息後，主動把訊息推送給client端，實時性高。弊端是server端工作量大，影響效能，其次是client端處理能力不同且client端的狀態不受server端的控制，如果client端不能及時處理訊息容易導致訊息堆積已經影響正常業務等。
-
pull方式是client迴圈從server端拉取訊息，主動權在client端，自己處理完一個訊息再去拉取下一個，缺點是迴圈的時間不好設定，時間太短容易忙等，浪費CPU資源，時間間隔太長client的處理能力會下降，有時候有些訊息會處理不及時。
長輪詢的方式可以結合兩者優點
- 檢查PullRequest物件中的ProcessQueue物件的dropped是否為true（在RebalanceService執行緒中為topic下的MessageQueue建立拉取訊息請求時要維護對應的ProcessQueue物件，若Consumer不再訂閱該topic則會將該物件的dropped置為true）；若是則認為該請求是已經取消的，則直接跳出該方法；
- 更新PullRequest物件中的ProcessQueue物件的時間戳（ProcessQueue.lastPullTimestamp）為當前時間戳；
- 檢查該Consumer是否執行中，即DefaultMQPushConsumerImpl.serviceState是否為RUNNING;若不是執行狀態或者是暫停狀態（DefaultMQPushConsumerImpl.pause=true），則呼叫PullMessageService.executePullRequestLater(PullRequest pullRequest, long timeDelay)方法延遲再拉取訊息，其中timeDelay=3000；該方法的目的是在3秒之後再次將該PullRequest物件放入PullMessageService. pullRequestQueue佇列中；並跳出該方法；
- 進行流控。若ProcessQueue物件的msgCount大於了消費端的流控閾值（DefaultMQPushConsumer.pullThresholdForQueue，預設值為1000），則呼叫PullMessageService.executePullRequestLater方法，在50毫秒之後重新該PullRequest請求放入PullMessageService.pullRequestQueue佇列中；並跳出該方法；
- 若不是順序消費（即DefaultMQPushConsumerImpl.consumeOrderly等於false），則檢查ProcessQueue物件的msgTreeMap:TreeMap<Long,MessageExt>變數的第一個key值與最後一個key值之間的差額，該key值表示查詢的佇列偏移量queueoffset；若差額大於閾值（由DefaultMQPushConsumer. consumeConcurrentlyMaxSpan指定，預設是2000），則呼叫PullMessageService.executePullRequestLater方法，在50毫秒之後重新將該PullRequest請求放入PullMessageService.pullRequestQueue佇列中；並跳出該方法；
- 以PullRequest.messageQueue物件的topic值為引數從RebalanceImpl.subscriptionInner: ConcurrentHashMap, SubscriptionData>中獲取對應的SubscriptionData物件，若該物件為null，考慮到併發的關係，呼叫executePullRequestLater方法，稍後重試；並跳出該方法；
- 若訊息模型為叢集模式（RebalanceImpl.messageModel等於CLUSTERING），則以PullRequest物件的MessageQueue變數值、type =READ_FROM_MEMORY（從記憶體中獲取消費進度offset值）為引數呼叫DefaultMQPushConsumerImpl. offsetStore物件（初始化為RemoteBrokerOffsetStore物件）的readOffset(MessageQueue mq, ReadOffsetType type)方法從本地記憶體中獲取消費進度offset值。若該offset值大於0 則置臨時變數commitOffsetEnable等於true否則為false；該offset值作為pullKernelImpl方法中的commitOffset引數，在Broker端拉取訊息之後根據commitOffsetEnable引數值決定是否用該offset更新訊息進度。該readOffset方法的邏輯是：以入參MessageQueue物件從RemoteBrokerOffsetStore.offsetTable:ConcurrentHashMap <MessageQueue,AtomicLong>變數中獲取消費進度偏移量；若該偏移量不為null則返回該值，否則返回-1；
- 當每次拉取訊息之後需要更新訂閱關係（由DefaultMQPushConsumer. postSubscriptionWhenPull參數列示，預設為false）並且以topic值引數從RebalanceImpl.subscriptionInner獲取的SubscriptionData物件的classFilterMode等於false（預設為false），則將sysFlag標記的第3個位元組置為1，否則該位元組置為0；
- 該sysFlag標記的第1個位元組置為commitOffsetEnable的值；第2個位元組（suspend標記）置為1；第4個位元組置為classFilterMode的值；
- 初始化匿名內部類PullCallback，實現了onSucess/onException方法； 該方法只有在非同步請求的情況下才會回撥；
- 呼叫底層的拉取訊息API介面：
PullAPIWrapper.pullKernelImpl
PullAPIWrapper.pullKernelImpl(MessageQueue mq, String subExpression, long subVersion,long offset, int maxNums, int sysFlag,long commitOffset,long brokerSuspendMaxTimeMillis, long timeoutMillis, CommunicationMode communicationMode, PullCallback pullCallback)方法進行訊息拉取操作。
將回撥類PullCallback傳入該方法中，當採用非同步方式拉取訊息時，在收到響應之後會回撥該回撥類的方法。
public void pullMessage(final PullRequest pullRequest) {
final ProcessQueue processQueue = pullRequest.getProcessQueue();
if (processQueue.isDropped()) {
log.info("the pull request[{}] is dropped.", pullRequest.toString());
return;
}
pullRequest.getProcessQueue().setLastPullTimestamp(System.currentTimeMillis());
try {
this.makeSureStateOK();
} catch (MQClientException e) {
log.warn("pullMessage exception, consumer state not ok", e);
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);
return;
}
if (this.isPause()) {
log.warn("consumer was paused, execute pull request later. instanceName={}, group={}", this.defaultMQPushConsumer.getInstanceName(), this.defaultMQPushConsumer.getConsumerGroup());
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_SUSPEND);
return;
}
long cachedMessageCount = processQueue.getMsgCount().get();
long cachedMessageSizeInMiB = processQueue.getMsgSize().get() / (1024 * 1024);
if (cachedMessageCount > this.defaultMQPushConsumer.getPullThresholdForQueue()) {
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
if ((queueFlowControlTimes++ % 1000) == 0) {
log.warn(
"the cached message count exceeds the threshold {}, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",
this.defaultMQPushConsumer.getPullThresholdForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);
}
return;
}
if (cachedMessageSizeInMiB > this.defaultMQPushConsumer.getPullThresholdSizeForQueue()) {
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
if ((queueFlowControlTimes++ % 1000) == 0) {
log.warn(
"the cached message size exceeds the threshold {} MiB, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",
this.defaultMQPushConsumer.getPullThresholdSizeForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);
}
return;
}
if (!this.consumeOrderly) {
if (processQueue.getMaxSpan() > this.defaultMQPushConsumer.getConsumeConcurrentlyMaxSpan()) {
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);
if ((queueMaxSpanFlowControlTimes++ % 1000) == 0) {
log.warn(
"the queue's messages, span too long, so do flow control, minOffset={}, maxOffset={}, maxSpan={}, pullRequest={}, flowControlTimes={}",
processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), processQueue.getMaxSpan(),
pullRequest, queueMaxSpanFlowControlTimes);
}
return;
}
} else {
if (processQueue.isLocked()) {
if (!pullRequest.isLockedFirst()) {
final long offset = this.rebalanceImpl.computePullFromWhere(pullRequest.getMessageQueue());
boolean brokerBusy = offset < pullRequest.getNextOffset();
log.info("the first time to pull message, so fix offset from broker. pullRequest: {} NewOffset: {} brokerBusy: {}",
pullRequest, offset, brokerBusy);
if (brokerBusy) {
log.info("[NOTIFYME]the first time to pull message, but pull request offset larger than broker consume offset. pullRequest: {} NewOffset: {}",
pullRequest, offset);
}
pullRequest.setLockedFirst(true);
pullRequest.setNextOffset(offset);
}
} else {
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);
log.info("pull message later because not locked in broker, {}", pullRequest);
return;
}
}
final SubscriptionData subscriptionData = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());
if (null == subscriptionData) {
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);
log.warn("find the consumer's subscription failed, {}", pullRequest);
return;
}
final long beginTimestamp = System.currentTimeMillis();
PullCallback pullCallback = new PullCallback() {
@Override
public void onSuccess(PullResult pullResult) {
if (pullResult != null) {
pullResult = DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(pullRequest.getMessageQueue(), pullResult,
subscriptionData);
switch (pullResult.getPullStatus()) {
case FOUND:
long prevRequestOffset = pullRequest.getNextOffset();
pullRequest.setNextOffset(pullResult.getNextBeginOffset());
long pullRT = System.currentTimeMillis() - beginTimestamp;
DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullRT(pullRequest.getConsumerGroup(),
pullRequest.getMessageQueue().getTopic(), pullRT);
long firstMsgOffset = Long.MAX_VALUE;
if (pullResult.getMsgFoundList() == null || pullResult.getMsgFoundList().isEmpty()) {
DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
} else {
firstMsgOffset = pullResult.getMsgFoundList().get(0).getQueueOffset();
DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullTPS(pullRequest.getConsumerGroup(),
pullRequest.getMessageQueue().getTopic(), pullResult.getMsgFoundList().size());
boolean dispatchToConsume = processQueue.putMessage(pullResult.getMsgFoundList());
DefaultMQPushConsumerImpl.this.consumeMessageService.submitConsumeRequest(
pullResult.getMsgFoundList(),
processQueue,
pullRequest.getMessageQueue(),
dispatchToConsume);
if (DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval() > 0) {
DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest,
DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval());
} else {
DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
}
}
if (pullResult.getNextBeginOffset() < prevRequestOffset
|| firstMsgOffset < prevRequestOffset) {
log.warn(
"[BUG] pull message result maybe data wrong, nextBeginOffset: {} firstMsgOffset: {} prevRequestOffset: {}",
pullResult.getNextBeginOffset(),
firstMsgOffset,
prevRequestOffset);
}
break;
case NO_NEW_MSG:
pullRequest.setNextOffset(pullResult.getNextBeginOffset());
DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);
DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
break;
case NO_MATCHED_MSG:
pullRequest.setNextOffset(pullResult.getNextBeginOffset());
DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);
DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);
break;
case OFFSET_ILLEGAL:
log.warn("the pull request offset illegal, {} {}",
pullRequest.toString(), pullResult.toString());
pullRequest.setNextOffset(pullResult.getNextBeginOffset());
pullRequest.getProcessQueue().setDropped(true);
DefaultMQPushConsumerImpl.this.executeTaskLater(new Runnable() {
@Override
public void run() {
try {
DefaultMQPushConsumerImpl.this.offsetStore.updateOffset(pullRequest.getMessageQueue(),
pullRequest.getNextOffset(), false);
DefaultMQPushConsumerImpl.this.offsetStore.persist(pullRequest.getMessageQueue());
DefaultMQPushConsumerImpl.this.rebalanceImpl.removeProcessQueue(pullRequest.getMessageQueue());
log.warn("fix the pull request offset, {}", pullRequest);
} catch (Throwable e) {
log.error("executeTaskLater Exception", e);
}
}
}, 10000);
break;
default:
break;
}
}
}
@Override
public void onException(Throwable e) {
if (!pullRequest.getMessageQueue().getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
log.warn("execute the pull request exception", e);
}
DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);
}
};
boolean commitOffsetEnable = false;
long commitOffsetValue = 0L;
if (MessageModel.CLUSTERING == this.defaultMQPushConsumer.getMessageModel()) {
commitOffsetValue = this.offsetStore.readOffset(pullRequest.getMessageQueue(), ReadOffsetType.READ_FROM_MEMORY);
if (commitOffsetValue > 0) {
commitOffsetEnable = true;
}
}
String subExpression = null;
boolean classFilter = false;
SubscriptionData sd = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());
if (sd != null) {
if (this.defaultMQPushConsumer.isPostSubscriptionWhenPull() && !sd.isClassFilterMode()) {
subExpression = sd.getSubString();
}
classFilter = sd.isClassFilterMode();
}
int sysFlag = PullSysFlag.buildSysFlag(
commitOffsetEnable, // commitOffset
true, // suspend
subExpression != null, // subscription
classFilter // class filter
);
try {
// 下面我們看繼續跟進這個方法，這個方法已經就是客戶端如何拉取訊息
this.pullAPIWrapper.pullKernelImpl(
pullRequest.getMessageQueue(),
subExpression,
subscriptionData.getExpressionType(),
subscriptionData.getSubVersion(),
pullRequest.getNextOffset(),
this.defaultMQPushConsumer.getPullBatchSize(),
sysFlag,
commitOffsetValue,
BROKER_SUSPEND_MAX_TIME_MILLIS,
CONSUMER_TIMEOUT_MILLIS_WHEN_SUSPEND,
// 訊息的通訊方式為非同步
CommunicationMode.ASYNC,
pullCallback
);
} catch (Exception e) {
log.error("pullKernelImpl exception", e);
this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);
}
}
傳送遠端請求拉取訊息
在MQClientAPIImpl.pullMessage方法中，根據入參communicationMode的值分為非同步拉取和同步拉取方式兩種。
無論是非同步方式拉取還是同步方式拉取，在傳送拉取請求之前都會構造一個ResponseFuture物件，以請求訊息的序列號為key值，存入NettyRemotingAbstract.responseTable:ConcurrentHashMap, ResponseFuture>變數中，對該變數有幾種情況會處理：
- 傳送失敗後直接刪掉responseTable變數中的相應記錄；
- 收到響應訊息之後，會以響應訊息中的序列號（由服務端根據請求訊息的序列號原樣返回）從responseTable中查詢ResponseFuture物件，並設定該物件的responseCommand變數。若是同步傳送會喚醒等待響應的ResponseFuture.waitResponse方法；若是非同步傳送會呼叫ResponseFuture.executeInvokeCallback()方法完成回撥邏輯處理；
- 在NettyRemotingClient.start()啟動時，也會初始化定時任務，該定時任務每隔1秒定期掃描responseTable列表，遍歷該列表中的ResponseFuture物件，檢查等待響應是否超時，若超時，則呼叫ResponseFuture. executeInvokeCallback()方法，並將該物件從responseTable列表中刪除；
public PullResult pullMessage(
final String addr,
final PullMessageRequestHeader requestHeader,
final long timeoutMillis,
final CommunicationMode communicationMode,
final PullCallback pullCallback
) throws RemotingException, MQBrokerException, InterruptedException {
RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.PULL_MESSAGE, requestHeader);
switch (communicationMode) {
case ONEWAY:
assert false;
return null;
case ASYNC:
this.pullMessageAsync(addr, request, timeoutMillis, pullCallback);
return null;
case SYNC:
return this.pullMessageSync(addr, request, timeoutMillis);
default:
assert false;
break;
}
return null;
}
同步拉取
對於同步傳送方式，呼叫MQClientAPIImpl.pullMessageSync(String addr, RemotingCommand request, long timeoutMillis)方法,大致步驟如下：
- 呼叫RemotingClient.invokeSync(String addr, RemotingCommand request, long timeoutMillis)方法：
- 獲取Broker地址的Channel資訊。根據broker地址從RemotingClient.channelTables:ConcurrentHashMap, ChannelWrapper>變數中獲取ChannelWrapper物件並返回該物件的Channel變數；若沒有ChannelWrapper物件則與broker地址建立新的連線並將連線資訊存入channelTables變數中，便於下次使用；
- 若NettyRemotingClient.rpcHook:RPCHook變數不為空（該變數在應用層初始化DefaultMQPushConsumer或者DefaultMQPullConsumer物件傳入該值），則呼叫RPCHook.doBeforeRequest(String remoteAddr, RemotingCommand request)方法；
- 呼叫NettyRemotingAbstract.invokeSyncImpl(Channel channel, RemotingCommand request, long timeoutMillis)方法，該方法的邏輯如下：
- A）使用請求的序列號（opaue）、超時時間初始化ResponseFuture物件；並將該ResponseFuture物件存入NettyRemotingAbstract.responseTable: ConcurrentHashMap變數中；
- B）呼叫Channel.writeAndFlush(Object msg)方法將請求物件RemotingCommand傳送給Broker；然後呼叫addListener(GenericFutureListener<? extends Future<? super Void>> listener)方法新增內部匿名類：該內部匿名類實現了ChannelFutureListener介面的operationComplete方法，在傳送完成之後回撥該監聽類的operationComplete方法，在該方法中，首先呼叫ChannelFuture. isSuccess()方法檢查是否傳送成功，若成功則置ResponseFuture物件的sendRequestOK等於true並退出此回撥方法等待響應結果；若不成功則置ResponseFuture物件的sendRequestOK等於false，然後從NettyRemotingAbstract.responseTable中刪除此請求序列號（opaue）的記錄，置ResponseFuture物件的responseCommand等於null，並喚醒ResponseFuture.waitResponse(long timeoutMillis)方法的等待；
- C）呼叫ResponseFuture.waitResponse(long timeoutMillis)方法等待響應結果；在傳送失敗或者收到響應訊息（詳見5.10.3小節）或者超時的情況下會喚醒該方法返回ResponseFuture.responseCommand變數值；
- D）若上一步返回的responseCommand值為null，則丟擲異常:若ResponseFuture.sendRequestOK為true，則丟擲RemotingTimeoutException異常，否則丟擲RemotingSendRequestException異常；
- E）若上一步返回的responseCommand值不為null，則返回responseCommand變數值；
- 若NettyRemotingClient.rpcHook: RPCHook變數不為空，則呼叫RPCHook.doAfterResponse(String remoteAddr, RemotingCommand request)方法；
- 以上一步的返回值RemotingCommand物件為引數呼叫MQClientAPIImpl. processPullResponse (RemotingCommand response)方法將返回物件解析並封裝成PullResultExt物件然後返回給呼叫者，響應訊息的結果狀態轉換如下：
- 若RemotingCommand物件的Code等於SUCCESS，則PullResultExt.pullStatus=FOUND；
- 若RemotingCommand物件的Code等於PULL_NOT_FOUND，則PullResultExt.pullStatus= NO_NEW_MSG；
- 若RemotingCommand物件的Code等於PULL_RETRY_IMMEDIATELY，則PullResultExt.pullStatus= NO_MATCHED_MSG；
- 若RemotingCommand物件的Code等於PULL_OFFSET_MOVED，則PullResultExt.pullStatus= OFFSET_ILLEGAL；
@Override
public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis)
throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException {
long beginStartTime = System.currentTimeMillis();
final Channel channel = this.getAndCreateChannel(addr);
if (channel != null && channel.isActive()) {
try {
if (this.rpcHook != null) {
this.rpcHook.doBeforeRequest(addr, request);
}
long costTime = System.currentTimeMillis() - beginStartTime;
if (timeoutMillis < costTime) {
throw new RemotingTimeoutException("invokeSync call timeout");
}
RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis - costTime);
if (this.rpcHook != null) {
this.rpcHook.doAfterResponse(RemotingHelper.parseChannelRemoteAddr(channel), request, response);
}
return response;
} catch (RemotingSendRequestException e) {
log.warn("invokeSync: send request exception, so close the channel[{}]", addr);
this.closeChannel(addr, channel);
throw e;
} catch (RemotingTimeoutException e) {
if (nettyClientConfig.isClientCloseSocketIfTimeout()) {
this.closeChannel(addr, channel);
log.warn("invokeSync: close socket because of timeout, {}ms, {}", timeoutMillis, addr);
}
log.warn("invokeSync: wait response timeout exception, the channel[{}]", addr);
throw e;
}
} else {
this.closeChannel(addr, channel);
throw new RemotingConnectException(addr);
}
}
getMQClientAPIImpl().pullMessage最終通過channel寫入並重新整理佇列中。然後在訊息服務端大體的處理邏輯是服務端收到新訊息請求後，如果佇列中沒有訊息不急於返回，通過一個迴圈狀態，每次waitForRunning一段時間預設5秒，然後再check，如果broker一直沒有新新訊息，第三次check的時間等到時間超過SuspendMaxTimeMills就返回空，如果在等待過程中收到了新訊息直接呼叫notifyMessageArriving函式返回請求結果。“長輪詢”的核心是，Broker端HOLD住客戶端過來的請求一小段時間，在這個時間內有新訊息到達，就利用現有的連線立刻返回訊息給 Consumer 。長輪詢的主動權掌握在consumer中，即使broker有大量的訊息堆積也不會主動推送給consumer。