That allows to set flags for rd_kafka_destroy_flags in the following manner:

     consumer.set_destroy_flags(RD_KAFKA_DESTROY_F_NO_CONSUMER_CLOSE);

It allows us to prevents potential hang during termination if consumer.close() is failing because of queued callback calls.

Refs:

• https://github.com/edenhill/librdkafka/blob/7269f0c6a225cd42dc7a44c5e081c464986d20ff/tests/0084-destroy_flags.c#L69
• rd_kafka_consumer_close gets stuck when polling events from consumer queue confluentinc/librdkafka#2077

More:

• Maybe it can also be used as a default (because Consumer destructor call consumer_close)
• or that flag maybe enabled automatically if an exception happens during consumer_close call in consumer destructor.
• Most probably that test can be enabled:

  cppkafka/tests/consumer_test.cpp

  Lines 245 to 260 in 006642c

  	// This test may fail due to what seems to be an rdkafka bug. Skip it for now until we're
  	// certain of what to do
  	TEST_CASE("Event consumption", "[!hide][consumer]") {
  	// Create a consumer and subscribe to the topic
  	Consumer consumer(make_consumer_config());
  	consumer.subscribe({ KAFKA_TOPICS[0] });
  	vector<rd_kafka_event_type_t> types = {
  	RD_KAFKA_EVENT_NONE
  	};
  	Queue queue = consumer.get_main_queue();
  	for (const auto type : types) {
  	const Event event = queue.next_event();
  	CHECK(event.get_type() == type);
  	}
  	}

Many thanks to @azat for help.