Consumer fell into an endless loop before it aborted in example_KafkaConsumer_Simple

[DittoWii]

I am running a simple example using _example_KafkaConsumer_Simple and example_KafkaProducer_Simple, the latter works perfectly, but it seems that the consumer can never subscribe correctly.
In function KafkaConsumer::subscribe in KafkaConsumer.h, I'm confused about the value of the variable _pendingEvent. So I use dbg, and found that the value of !_pendingEvent in line503 seems uncorrect, so KAFKA_API_DO_LOG(Log::Level::Notice, "subscribed, topics[%s]", topicsStr.c_str()); will never be executed, and the function KafkaConsumer::subscribe will never return, causing core dumped evetually.
So is this my problem or ....
Looking forward to your reply.

[DittoWii]

and I found that sometimes it works, but sometimes not, am I using it wrong?

[c4pQ]

I believe you have your application crashing with core dump because of uncaught kafka::Exception.

As for _pendingEvent, from code I see:

1. initially you have it set here - https://github.com/morganstanley/modern-cpp-kafka/blob/main/include/kafka/KafkaConsumer.h#L484
2. then it's polling
3. then you either have:
   3.1. rebalance callback called and having event.reset() - https://github.com/morganstanley/modern-cpp-kafka/blob/main/include/kafka/KafkaConsumer.h#L920
   3.2. or nothing happened during poll and you continue with exception

What do you use for test purposes? Kafka container? Something in cloud? Mock cluster from librdkafka?