Kafka消费者Heartbeat分析

消费者会定期向GroupCoordinator发送HeartbeatRequest来确定 彼此在线，也就是说告诉GroupCoordinator我还活着，或者也判断GrooupCoordinator是否还活着

 

HeartbeatRequest的组成：它是由groupId，generationId，memberId.

HeartbeatResponse组成：它只有一个errorCode

HeartbeatThread是专门处理Heartbeat的一个线程类

源码分析：

一 Heartbeat

// session到期时间
private final long sessionTimeout;
// 发送heartbeat的间隔
private final long heartbeatInterval;
// 最大的poll间隔
private final long maxPollInterval;
// 重试时间
private final long retryBackoffMs;

// 上一次发送heartbeat时间
private volatile long lastHeartbeatSend; // volatile since it is read by metrics
// 上一次接收heartbeat响应时间
private long lastHeartbeatReceive;
private long lastSessionReset;
private long lastPoll;
// heartbeat是否成功
private boolean heartbeatFailed;

 

 

// 更新lastPoll时间
public void poll(long now) {
    this.lastPoll = now;
}

// 更新上一次心跳发送时间
public void sentHeartbeat(long now) {
    this.lastHeartbeatSend = now;
    this.heartbeatFailed = false;
}

// 更新心跳状态为失败
public void failHeartbeat() {
    this.heartbeatFailed = true;
}
// 更新上次接收心跳时间
public void receiveHeartbeat(long now) {
    this.lastHeartbeatReceive = now;
}

// 更新上一次心跳发送时间
public boolean shouldHeartbeat(long now) {
    return timeToNextHeartbeat(now) == 0;
}

 

// 判断session是否过期
public boolean sessionTimeoutExpired(long now) {
    return now - Math.max(lastSessionReset, lastHeartbeatReceive) > sessionTimeout;
}

 

// 判断poll是否过期
public boolean pollTimeoutExpired(long now) {
    return now - lastPoll > maxPollInterval;
}

 

二 HeartbeatThread

public void run() {
        try {
            while (true) {
                synchronized (AbstractCoordinator.this) {
                    if (closed)
                        return;
                    // 是否enable HeartbeatThread
                    if (!enabled) {
                        AbstractCoordinator.this.wait();
                        continue;
                    }
                    // 如果消费者状态如果不是STABLE(消费者已经加入消费者组，并且开始发送心跳)
                    if (state != MemberState.STABLE) {
                        // 可能是消费者离开消费者组或者coordinator把我们踢了，所以需要disable heartbeats，等待主线程重新加入
                        disable();
                        continue;
                    }

                    client.pollNoWakeup();
                    long now = time.milliseconds();
                    // 检测GroupCoordinator是否已连接
                    if (coordinatorUnknown()) {
                        // 如果没有连接，则查找GroupCoordinator,并返回一个请求结果
                        if (findCoordinatorFuture == null)
                            lookupCoordinator();
                        else
                            AbstractCoordinator.this.wait(retryBackoffMs);
                    } else if (heartbeat.sessionTimeoutExpired(now)) {// 检测HeartbeatRespose是否超时
                        // 如果超时，则认为GroupCoordinator宕机，调用coordinatorDead方法清空unsent集合中的
                        // 请求，将coordinator 设置为null,表示将重新选举GroupCoordinator
                        coordinatorDead();
                    } else if (heartbeat.pollTimeoutExpired(now)) {
                            // the poll timeout has expired, which means that the foreground thread has stalled
                            // in between calls to poll(), so we explicitly leave the group.
                        maybeLeaveGroup();
                    } else if (!heartbeat.shouldHeartbeat(now)) {// 没有到心跳请求的发送时间，等待
                        // poll again after waiting for the retry backoff in case the heartbeat failed or the
                        // coordinator disconnected
                        AbstractCoordinator.this.wait(retryBackoffMs);
                    } else {
                        // 更新lastHeartbeatSend的时间,并且初始化heartbeatFailed
                        heartbeat.sentHeartbeat(now);
                        // 构造HeartbeatRequest对象，通过ConsumerClientNetwork添加到unsent队列，
                        // 等待发送，结果HeartbeatResponseHandler处理后返回一个RequestFuture
                        // 添加RequestFutureListener监听器，如果成功更新lastHeartbeatReceive时间
                        // 如果失败，则需要看情况：
                        // # 如果是正处于rebalance过程还是更新lastHeartbeatReceive时间
                        // # 标记heartbeat请求失败
                        sendHeartbeatRequest().addListener(new RequestFutureListener<Void>() {
                            @Override
                            public void onSuccess(Void value) {
                                synchronized (AbstractCoordinator.this) {
                                    heartbeat.receiveHeartbeat(time.milliseconds());
                                }
                            }

                            @Override
                            public void onFailure(RuntimeException e) {
                                synchronized (AbstractCoordinator.this) {
                                    if (e instanceof RebalanceInProgressException) {
                                        // it is valid to continue heartbeating while the group is rebalancing. This
                                        // ensures that the coordinator keeps the member in the group for as long
                                        // as the duration of the rebalance timeout. If we stop sending heartbeats,
                                        // however, then the session timeout may expire before we can rejoin.
                                        heartbeat.receiveHeartbeat(time.milliseconds());
                                    } else {
                                        heartbeat.failHeartbeat();

                                        // wake up the thread if it's sleeping to reschedule the heartbeat
                                        AbstractCoordinator.this.notify();
                                    }
                                }
                            }
                        });
                    }
                }
            }
        } catch (InterruptedException e) {
            log.error("Unexpected interrupt received in heartbeat thread for group {}", groupId, e);
            this.failed.set(new RuntimeException(e));
        } catch (RuntimeException e) {
            log.error("Heartbeat thread for group {} failed due to unexpected error" , groupId, e);
            this.failed.set(e);
        }
    }

}

 

三sendHeartbeatRequest

// 构造HeartbeatRequest对象，通过ConsumerClientNetwork添加到unsent队列，
// 等待发送，结果HeartbeatResponseHandler处理后返回一个RequestFuture
synchronized RequestFuture<Void> sendHeartbeatRequest() {
    HeartbeatRequest req = new HeartbeatRequest(this.groupId, this.generation.generationId, this.generation.memberId);
    return client.send(coordinator, ApiKeys.HEARTBEAT, req)
            .compose(new HeartbeatResponseHandler());
}

 

四 HeartbeatResponse的处理

private class HeartbeatResponseHandler extends CoordinatorResponseHandler<HeartbeatResponse, Void> {

    // 将ClientResponse转换成HeartbeatResponse
    @Override
    public HeartbeatResponse parse(ClientResponse response) {
        return new HeartbeatResponse(response.responseBody());
    }

    @Override
    public void handle(HeartbeatResponse heartbeatResponse, RequestFuture<Void> future) {
        sensors.heartbeatLatency.record(response.requestLatencyMs());
        Errors error = Errors.forCode(heartbeatResponse.errorCode());
        if (error == Errors.NONE) {// 心跳正常，没有错误
            log.debug("Received successful heartbeat response for group {}", groupId);
            future.complete(null);
        } else if (error == Errors.GROUP_COORDINATOR_NOT_AVAILABLE
                || error == Errors.NOT_COORDINATOR_FOR_GROUP) {// 找不到服务器端的GroupCoordinator
            log.debug("Attempt to heart beat failed for group {} since coordinator {} is either not started or not valid.",
                    groupId, coordinator());
            coordinatorDead();// 清空unsent集合中请求与，并置空coordinator
            future.raise(error);
        } else if (error == Errors.REBALANCE_IN_PROGRESS) {// 如果正在rebalance
            log.debug("Attempt to heart beat failed for group {} since it is rebalancing.", groupId);
            requestRejoin();// 重新发送JoinGroupRequest
            future.raise(Errors.REBALANCE_IN_PROGRESS);
        } else if (error == Errors.ILLEGAL_GENERATION) {//如果Generation不合法
            log.debug("Attempt to heart beat failed for group {} since generation id is not legal.", groupId);
            resetGeneration();//重新设置Generation
            future.raise(Errors.ILLEGAL_GENERATION);
        } else if (error == Errors.UNKNOWN_MEMBER_ID) {// 如果member未知
            log.debug("Attempt to heart beat failed for group {} since member id is not valid.", groupId);
            resetGeneration();//重新设置Generation
            future.raise(Errors.UNKNOWN_MEMBER_ID);
        } else if (error == Errors.GROUP_AUTHORIZATION_FAILED) {
            future.raise(new GroupAuthorizationException(groupId));
        } else {
            future.raise(new KafkaException("Unexpected error in heartbeat response: " + error.message()));
        }
    }
}