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()));
}
}
}