public Set<TopicPartition> assignment() {
        acquireAndEnsureOpen();
        try {
            return Collections.unmodifiableSet(this.subscriptions.assignedPartitions());
        } finally {
            release();
        }
    }
A client that consumes records from a Kafka cluster using the {@link GroupProtocol#CLASSIC classic group protocol}.
In this implementation, all network I/O happens in the thread of the application making the call.

<p/>

This {@link ConsumerDelegate} implementation exists for backward compatibility to allow users to continue to use
the classic group protocol (pre-KIP 848).

<p/>

<em>Note:</em> This class should not be invoked directly; users should instead create and use the
{@link KafkaConsumer} API as before.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ClassicKafkaConsumer.java