fn spawn_reader(
cfg: ReaderConfig,
sender: Sender<(ReadStatData, WriteConfig, usize)>,
) -> JoinHandle<Result<(), ReadStatError>>Expand description
Spawns the reader thread that parses row chunks and sends them to sender.
Any chunk error is returned from the thread so it propagates to the exit
code — chunks must never be silently dropped, as that would corrupt the
output. The returned handle is joined (via join_reader) by whichever
write strategy drains the channel.