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kafka源码---消费者(2)_disableheartbeat

作者：小小林熬夜学编程 | 2024-02-21 17:55:35

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disableheartbeat

继续接着上一下消费者的知识点，本节我们将追踪消费者中最重要的rebalance代码和offset提交代码！

一，rebalance

首先，我们看看哪些情况会触发rebalance:

1.有新的consumer 加入

2.有consumer宕机，可能网络延迟，规定时间内没有进行heartbean

3.有消费者主动退出 consumer gorup

4.conmuser group订阅的topic出现 partition数量变化

5.消费者调用unsubscrible() 取消对topic的订阅

我们把rebalance整体分为三个阶段，分别寻找GroupCoordinator,当一个consumer上线的时候，不知道我们订阅的topic，在哪个node上面。第二阶段：进行join Group，发送JoinGroupRequest请求，处理response。第三阶段：进入Synchronizing Group State阶段，

1.1 第一阶段

找到GroupCoordinator，我们随便向集群中的任意node,发送一个GroupCoordinatorRequest请求，在该请求里面就只带了groupId这一个变量，集群收到之后，返会GroupCoordinatorResponse响应，包含了coordinator节点的id,host,port三个值，还有错误码（便于查找问题,short类型）

注意poll()是整个rebalance流程都会走的主方法，它位于ConsumerCoordinator类中


public void poll(long now, long remainingMs) {
    invokeCompletedOffsetCommitCallbacks();
 
    if (subscriptions.partitionsAutoAssigned()) {
        if (coordinatorUnknown()) { 
            ensureCoordinatorReady();//第一阶段
            now = time.milliseconds();
        }
....
}

我们首先看一下if中的判断方法，如果coordinator不存在，那么我们就需要通过GroupCoodinatorRequest请求找到coordinator。


public boolean coordinatorUnknown() {
    return coordinator() == null;
}

现在步入正题，发送request,处理response,这里的方法，只是发送request的入口，真正的send()还需要深入

它位于AbstractCoordinator类中，也就是ConsumerCoordinator的父类

----- request创建与发送 -----------


protected synchronized boolean ensureCoordinatorReady(long startTimeMs, long timeoutMs) {
    long remainingMs = timeoutMs;
    while (coordinatorUnknown()) {
        RequestFuture<Void> future = lookupCoordinator(); //发送【入】
        client.poll(future, remainingMs);  //等待结果
        if (future.failed()) {
            if (future.isRetriable()) {
                remainingMs = timeoutMs - (time.milliseconds() - startTimeMs);
                if (remainingMs <= 0)
                    break;
                client.awaitMetadataUpdate(remainingMs); //阻塞更新metadata中记录的集群元数据，重新执行
            } else
                throw future.exception();
        } else if (coordinator != null && client.connectionFailed(coordinator)) {
            //找到了，但是网络连接失败，清空unsent，重新发送
            coordinatorDead();
            time.sleep(retryBackoffMs);
        }
        remainingMs = timeoutMs - (time.milliseconds() - startTimeMs);
        if (remainingMs <= 0)
            break;
    }
    return !coordinatorUnknown();
}

我们要了解GroupDoordinatorRequest是如何产生的，所以我们进入lookupCoordinator()方法中：


protected synchronized RequestFuture<Void> lookupCoordinator() {
    if (findCoordinatorFuture == null) {
        // find a node to ask about the coordinator
        Node node = this.client.leastLoadedNode();  //找一个负载最小的node 发送data
        if (node == null) {
            log.debug("No broker available to send GroupCoordinator request");
            return RequestFuture.noBrokersAvailable();
        } else
            findCoordinatorFuture = sendGroupCoordinatorRequest(node);//【入】
    }
    return findCoordinatorFuture;
}

它的主要功能是，找一个负载最小的node节点，用来发送信息，然后再深入：


private RequestFuture<Void> sendGroupCoordinatorRequest(Node node) {
    // initiate the group metadata request
    log.debug("Sending GroupCoordinator request to broker {}", node);
    FindCoordinatorRequest.Builder requestBuilder =
            new FindCoordinatorRequest.Builder(FindCoordinatorRequest.CoordinatorType.GROUP, this.groupId);
    return client.send(node, requestBuilder)
                 .compose(new GroupCoordinatorResponseHandler()); //发送
}

可以看到，我们找到了CoordinatorRequest的构建了，直接new出来的，参数也很简单，就是一个grooupId,这个Builder类是FindCoorDinatorRequest的内部类，这样设计的原因是什么？


public static class Builder extends AbstractRequest.Builder<FindCoordinatorRequest> {
    private final String coordinatorKey; //groupId
    private final CoordinatorType coordinatorType; //Group
    private final short minVersion;
...
}

最后，使用client发送：注意这里的CompletionHandler，处理器，它也是内部类。


public RequestFuture<ClientResponse> send(Node node, AbstractRequest.Builder<?> requestBuilder) {
    long now = time.milliseconds();
    RequestFutureCompletionHandler completionHandler = new RequestFutureCompletionHandler();
    ClientRequest clientRequest = client.newClientRequest(node.idString(), requestBuilder, now, true,
            completionHandler);
    unsent.put(node, clientRequest);
 
    // wakeup the client in case it is blocking in poll so that we can send the queued request
    client.wakeup();
    return completionHandler.future;
}

--------- response 处理 ---------------

我们分析一下回调过程：

首先我们在send()里面返回的是一个future，这个future是什么？

是一个ClinetResponse,我们还有对应的ClientRequest。我们再看一下ClientResponse字段：

ClientResponse类


public class ClientResponse {
    private final RequestHeader requestHeader;
    private final RequestCompletionHandler callback;  //★
    private final String destination;
    private final long receivedTimeMs;
    private final long latencyMs;
    private final boolean disconnected;
    private final UnsupportedVersionException versionMismatch;
    private final AbstractResponse responseBody;
...
}

注意★这个字段，我们回忆一下，调用send()方法的时候，后面还有一个尾巴：

这里就对应上了，所以我们查看这个responseHandler是如何处理的：


public void onSuccess(ClientResponse resp, RequestFuture<Void> future) {
...
    if (error == Errors.NONE) {    //无错误
        synchronized (AbstractCoordinator.this) {  //给coordinator赋值
            AbstractCoordinator.this.coordinator = new Node(
                    Integer.MAX_VALUE - findCoordinatorResponse.node().id(),
                    findCoordinatorResponse.node().host(),
                    findCoordinatorResponse.node().port());
            log.info("Discovered coordinator {}", coordinator);
            client.tryConnect(coordinator);
            heartbeat.resetTimeouts(time.milliseconds());
        }
        future.complete(null);
    } else if (error == Errors.GROUP_AUTHORIZATION_FAILED) {
        future.raise(new GroupAuthorizationException(groupId));
    } else {
        log.debug("Group coordinator lookup failed: {}", error.message());
        future.raise(error);
    }
}

好了，我们到这里就成功的把coordinator初始化了！

1.2 第二阶段

成功找到GroupCoordinator之后，进入第二阶段，消费者向GroupCoordinator发送JoinGroupRequest请求，并处理响应。

入口同样在ConsumerCoordinator类中的poll()方法中


    public void poll(long now, long remainingMs) {
...
      if (needRejoin()) {
          if (subscriptions.hasPatternSubscription())
               client.ensureFreshMetadata();
         ensureActiveGroup();  //【入】第二阶段
         now = time.milliseconds();
       }
        ...
    }

调用方法判断是否需要join()


public boolean needRejoin() {
    if (!subscriptions.partitionsAutoAssigned())  //是否为自动分区分配订阅模式
        return false;
    // we need to rejoin if we performed the assignment and metadata has changed
    if (assignmentSnapshot != null && !assignmentSnapshot.equals(metadataSnapshot))
        return true;
    // we need to join if our subscription has changed since the last join
    if (joinedSubscription != null && !joinedSubscription.equals(subscriptions.subscription()))
        return true;
    return super.needRejoin();
}

好了，现在我们需要rejoin()，并且GroupCoordinator已经找到了，继续跟踪

来到AbstractCoordinator类中，ConsumerCoordinator的父类


public void ensureActiveGroup() {
    ensureCoordinatorReady(); //保证 coordinator已经找到
    startHeartbeatThreadIfNeeded();  //心跳检测 开启
    joinGroupIfNeeded();   //是否需要join
}

看一下第二个方法，开启心跳检测，内容简单。


private synchronized void startHeartbeatThreadIfNeeded() {
    if (heartbeatThread == null) {
        heartbeatThread = new HeartbeatThread();
        heartbeatThread.start();
    }
}

现在进入正题：joinGroupIfNeeded()方法：


void joinGroupIfNeeded() {
    while (needRejoin() || rejoinIncomplete()) {
        ensureCoordinatorReady();  //确保 找到了groupCoordinator
        if (needsJoinPrepare) {
            onJoinPrepare(generation.generationId, generation.memberId); //1.预处理
            needsJoinPrepare = false;
        }
 
        RequestFuture<ByteBuffer> future = initiateJoinGroup(); //2.【入】
        client.poll(future); //阻塞等待完成请求
 
        if (future.succeeded()) {
            onJoinComplete(generation.generationId, generation.memberId, generation.protocol, future.value());
            resetJoinGroupFuture();
            needsJoinPrepare = true;
        } else {
            resetJoinGroupFuture();
            RuntimeException exception = future.exception();
            if (exception instanceof UnknownMemberIdException ||
                    exception instanceof RebalanceInProgressException ||
                    exception instanceof IllegalGenerationException)
                continue;
            else if (!future.isRetriable())
                throw exception;
            time.sleep(retryBackoffMs);
        }
    }
}

看第一个1.预处理 onJoinPrepare()方法，


protected void onJoinPrepare(int generation, String memberId) {
    // commit offsets prior to rebalance if auto-commit enabled
    maybeAutoCommitOffsetsSync(rebalanceTimeoutMs);     //进行一次同步offset操作
 
    // execute the user's callback before rebalance
    ConsumerRebalanceListener listener = subscriptions.listener();
    log.info("Revoking previously assigned partitions {}", subscriptions.assignedPartitions());
    try {
        Set<TopicPartition> revoked = new HashSet<>(subscriptions.assignedPartitions());
        listener.onPartitionsRevoked(revoked);
    } catch (WakeupException | InterruptException e) {
        throw e;
    } catch (Exception e) {
        log.error("User provided listener {} failed on partition revocation", listener.getClass().getName(), e);
    }
 
    isLeader = false;
    subscriptions.resetGroupSubscription();
}

第二个方法，----- request创建与发送 -----------


private synchronized RequestFuture<ByteBuffer> initiateJoinGroup() {
    if (joinFuture == null) {
        disableHeartbeatThread();  //中断 心跳检测
        state = MemberState.REBALANCING;
        joinFuture = sendJoinGroupRequest(); //【入】 发送
        joinFuture.addListener(new RequestFutureListener<ByteBuffer>() {
            @Override
            public void onSuccess(ByteBuffer value) {
                synchronized (AbstractCoordinator.this) {
                    log.info("Successfully joined group with generation {}", generation.generationId);
                    state = MemberState.STABLE;
                    rejoinNeeded = false;
                    if (heartbeatThread != null)
                        heartbeatThread.enable();
                }
            }
            @Override
            public void onFailure(RuntimeException e) {
                synchronized (AbstractCoordinator.this) {
                    state = MemberState.UNJOINED;
                }
            }
        });
    }
    return joinFuture;
}

继续深入，创建request


private RequestFuture<ByteBuffer> sendJoinGroupRequest() {
    if (coordinatorUnknown())
        return RequestFuture.coordinatorNotAvailable();
    JoinGroupRequest.Builder requestBuilder = new JoinGroupRequest.Builder(
            groupId,
            this.sessionTimeoutMs,
            this.generation.memberId,
            protocolType(),
            metadata()).setRebalanceTimeout(this.rebalanceTimeoutMs);
    return client.send(coordinator, requestBuilder)
            .compose(new JoinGroupResponseHandler());
}

到这里，套路就和基本的发送request讨论一样了，绑定一个回调方法，处理response。

request字段


    private final String groupId;
    private final int sessionTimeout;  //超过该时间没有收到心跳，则任务consumer下线
    private final int rebalanceTimeout;
    private final String memberId;   //GroupCoordinator分配给消费者的ID
    private final String protocolType;  //实现的协议，默认是“consumer”
    private final List<ProtocolMetadata> groupProtocols;  //针对不同的PartitionAssignor，序列化后的消费者的订阅信息

--------- response 处理 ---------------

我们这里直接跳转道response的处理，位于JoinGroupResponseHandler类中


if (error == Errors.NONE) {
    log.debug("Received successful JoinGroup response: {}", joinResponse);
    sensors.joinLatency.record(response.requestLatencyMs());
 
    synchronized (AbstractCoordinator.this) {
        if (state != MemberState.REBALANCING) {
            // if the consumer was woken up before a rebalance completes, we may have already left
            // the group. In this case, we do not want to continue with the sync group.
            future.raise(new UnjoinedGroupException());
        } else { //走这里
            AbstractCoordinator.this.generation = new Generation(joinResponse.generationId(),
                    joinResponse.memberId(), joinResponse.groupProtocol());
            if (joinResponse.isLeader()) {  //如果是leader消费者
                onJoinLeader(joinResponse).chain(future);
            } else { //跟随者
                onJoinFollower().chain(future);
            }
        }
    }
}

response字段：


    private final int throttleTimeMs;
    private final Errors error;
    private final int generationId;  //GroupCoordinator分配的年代信息
    private final String groupProtocol;  //GroupCoordinator选择的Assignor
    private final String memberId;  // GroupCoordinator分配给消费者的Id
    private final String leaderId;  //leader的memberId
    private final Map<String, ByteBuffer> members;  //对应消费者的订阅信息

这里就重点了。返回结果中，如果consumer被定位为leader，则要执行分区分配，并且把分区分配的结果，返回给server,而follower则要再发送request，获得分配分区后的结果。

1.首先看一下follower()，这个简单一点


private RequestFuture<ByteBuffer> onJoinFollower() {
    SyncGroupRequest.Builder requestBuilder =
            new SyncGroupRequest.Builder(groupId, generation.generationId, generation.memberId,
                    Collections.<String, ByteBuffer>emptyMap());
    return sendSyncGroupRequest(requestBuilder);
}

2. onJoinLeader()

它与follower()方法差不多，只不过多了一个分区分配的结果放到request中，而follower的request放入的是一个空集合。


private RequestFuture<ByteBuffer> onJoinLeader(JoinGroupResponse joinResponse) {
    try {
        Map<String, ByteBuffer> groupAssignment = performAssignment(joinResponse.leaderId(), joinResponse.groupProtocol(),
                joinResponse.members());
 
        SyncGroupRequest.Builder requestBuilder =
                new SyncGroupRequest.Builder(groupId, generation.generationId, generation.memberId, groupAssignment);
        return sendSyncGroupRequest(requestBuilder);
}

具体的分区分配，我们在消费者(1)中讲解了，主要就是调用AbstractPartitionAssignor的assign方法，然后调用对应策略的assign()方法，然后获得最后分配的结果。

这里我们按栈的方式慢慢的返回结果：

得到future之后，第一个（这些之前都出场过的）


public void onSuccess(ByteBuffer value) {
    synchronized (AbstractCoordinator.this) {
        state = MemberState.STABLE;
        rejoinNeeded = false;
        if (heartbeatThread != null)
            heartbeatThread.enable();
    }
}


if (future.succeeded()) {
    onJoinComplete(generation.generationId, generation.memberId, generation.protocol, future.value());
    resetJoinGroupFuture();
    needsJoinPrepare = true;
}

这个OnJoinComplete()方法，也是很重要的，进入第三阶段的时候，讲解

1.3 第三阶段

完成分区分配之后，进入Synchronizing Group state阶段，主要逻辑是向GroupCoordinator发送SyncGroupRequest请求并处理SyncGroupResponse响应。

我们知道，在分区分配完成之后，leader和follower都会发送这个请求，逻辑简单，我们这里主要是看它是如何处理response的，进入handler代码：


private class SyncGroupResponseHandler extends CoordinatorResponseHandler<SyncGroupResponse, ByteBuffer> {
   @Override
   public void handle(SyncGroupResponse syncResponse,
                      RequestFuture<ByteBuffer> future) {
       Errors error = syncResponse.error();
       if (error == Errors.NONE) {
           sensors.syncLatency.record(response.requestLatencyMs());
               //传播分区分配的结果
           future.complete(syncResponse.memberAssignment());
       }

其实，真正处理结果的地方，是在前面的listener的处理方案中的OnJoinComplete()中，位于ConsumerCoordinator


protected void onJoinComplete(int generation,
                              String memberId,
                              String assignmentStrategy,
                              ByteBuffer assignmentBuffer) {
    if (!isLeader)
        assignmentSnapshot = null;
    //查找使用的分配策略
    PartitionAssignor assignor = lookupAssignor(assignmentStrategy);  //对比策略，本地是否存在
    if (assignor == null)
        throw new IllegalStateException("Coordinator selected invalid assignment protocol: " + assignmentStrategy);
    //2.反序列化，更新assignment
    Assignment assignment = ConsumerProtocol.deserializeAssignment(assignmentBuffer);
    //将needsFetchCommittedOffsets设置为true，运行从服务端获取最近一次的提交的offset
    subscriptions.needRefreshCommits();
    //填充assignment集合
    subscriptions.assignFromSubscribed(assignment.partitions());
    Set<String> addedTopics = new HashSet<>();
    for (TopicPartition tp : subscriptions.assignedPartitions()) {
        if (!joinedSubscription.contains(tp.topic()))
            addedTopics.add(tp.topic());
    }
 
    if (!addedTopics.isEmpty()) {
        Set<String> newSubscription = new HashSet<>(subscriptions.subscription());
        Set<String> newJoinedSubscription = new HashSet<>(joinedSubscription);
        newSubscription.addAll(addedTopics);
        newJoinedSubscription.addAll(addedTopics);
 
        this.subscriptions.subscribeFromPattern(newSubscription);
        this.joinedSubscription = newJoinedSubscription;
    }
    this.metadata.setTopics(subscriptions.groupSubscription());
    client.ensureFreshMetadata();
    //回调函数
    assignor.onAssignment(assignment);
 
    this.nextAutoCommitDeadline = time.milliseconds() + autoCommitIntervalMs;
 
    ConsumerRebalanceListener listener = subscriptions.listener();
    log.info("Setting newly assigned partitions {}", subscriptions.assignedPartitions());
    try {
        Set<TopicPartition> assigned = new HashSet<>(subscriptions.assignedPartitions());
        listener.onPartitionsAssigned(assigned);
    } catch (WakeupException | InterruptException e) {
        throw e;
    } catch (Exception e) {
        log.error("User provided listener {} failed on partition assignment", listener.getClass().getName(), e);
    }
}

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