背景
我們已知ConsumerNetworkClient是對NetworkClient的封裝，而消費者與服務器的交互分為兩條線程
- KafkaConsumer.poll() 業務線程
- HeartbeatThread 心跳線程
初始化
在激活消費者組狀態時，會啟動心跳線程。
心跳線程啟動后，只要沒銷毀，就會繼續執行，期間可能被沉默，也可能由于父對象的coordinator變化而改變發送心跳對象。
AbstractCoordinator:
public void ensureActiveGroup() {
// always ensure that the coordinator is ready because we may have been disconnected
// when sending heartbeats and does not necessarily require us to rejoin the group.
ensureCoordinatorReady();
startHeartbeatThreadIfNeeded();
joinGroupIfNeeded();
}
private synchronized void startHeartbeatThreadIfNeeded() {
if (heartbeatThread == null) {
heartbeatThread = new HeartbeatThread();
heartbeatThread.start();
}
}
發送心跳
向父對象的coordinator發送心跳。
// visible for testing
synchronized RequestFuture<Void> sendHeartbeatRequest() {
log.debug("Sending Heartbeat request to coordinator {}", coordinator);
HeartbeatRequest.Builder requestBuilder =
new HeartbeatRequest.Builder(this.groupId, this.generation.generationId, this.generation.memberId);
return client.send(coordinator, requestBuilder)
.compose(new HeartbeatResponseHandler());
}
心跳間歇
HeartbeatThread主循環在判斷下次心跳時間未到時會阻塞。
else if (!heartbeat.shouldHeartbeat(now)) {
// poll again after waiting for the retry backoff in case the heartbeat failed or the
// coordinator disconnected
AbstractCoordinator.this.wait(retryBackoffMs);
}
等待時間為heartbeatInterval，但為什么等待retryBackoffMs？
