[Q] Async prefetch next batch while model is doing forward pass

[GM-git-dotcom]

Hi,

Love the repo for the self-explanatory code and fun comments!

I would appreciate it if you could explain how the next batch is asynchronously being fetched in train.py:

https://github.com/karpathy/nanoGPT/blob/325be85d9be8c81b436728a420e85796c57dba7e/train.py#L299-L305

At the outset, without explicitly using something like asyncio, the execution seemed sequential to me. Apologies for the potential triviality, thanks!