@Override
    public ConsumerGroupMetadata groupMetadata() {
        acquireAndEnsureOpen();
        try {
            maybeThrowInvalidGroupIdException();
            return coordinator.groupMetadata();
        } finally {
            release();
        }
    }
@throws KafkaException if the rebalance callback throws exception
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ClassicKafkaConsumer.java