Function shared_range_stream 

fn shared_range_stream<F, Fut>(
    receiver: Receiver<Option<Arc<RangeCacheDelivery>>>,
    build: F,
) -> BoxedRecordBatchStream
where
    F: FnOnce() -> Fut + Send + 'static,
    Fut: Future<Output = Result<(BoxedRecordBatchStream, usize)>> + Send + 'static,

Waiting is lazy, but the producer is independent of every consumer.