fn new_candidate_channel_list(
num_partitions: usize,
) -> (Vec<Option<UnboundedSender<Result<SeriesReaderInput>>>>, Vec<Option<CandidateReceiver>>, Arc<AtomicUsize>)fn new_candidate_channel_list(
num_partitions: usize,
) -> (Vec<Option<UnboundedSender<Result<SeriesReaderInput>>>>, Vec<Option<CandidateReceiver>>, Arc<AtomicUsize>)