Re: Parallel guix builds can trample?

[Phil]

Maxime Devos writes:

> Maybe 'latest-repository-commit' and 'update-cached-checkout' commit
> can be modified to not use 'switch-to-ref', and instead directly ask
> libgit ‘what's the tree structure of commit cabba9e’ and call a
> procedure like 'add-file-tree-to-store'.  That would avoid lock files,
> creating separate directories for concurrent checkouts, ...

Thanks Maxime - I'll take a look at this as an option.

One option I was thinking of is to make this SHA call dependent on the
branch as well as the URL:
https://github.com/guix-mirror/guix/blob/9f526f5dad5f4af69d158c50369e182305147f3b/guix/git.scm#L131-L133

Technically this still leaves a race condition if someone were to do
parallel builds on the same branch however, so to completely solve the
problem I think we'd have make the SHA call on repo+commit-id.

This obviously limit the utility of the cache.

To mitigate performance concerns, I think it's possible to set the
branches and depth in git such that we only clone the bare-bones only?.