@Override
    public void close() {
        lock.lock();
        try {
            idempotentCloser.close(
                    this::drainAll,
                    () -> log.warn("The fetch buffer was already closed")
            );
        } finally {
            lock.unlock();
        }
    }
Return the set of {@link TopicIdPartition partitions} for which we have data in the buffer.

@return {@link TopicIdPartition Partition} set
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ShareFetchBuffer.java