Race condition in `cabal build`

[isomorpheme]

Describe the bug
Running multiple cabal builds at the same time will crash at least one of them with an error ghc-pkg-{...}: cannot create: {...}/dist-newstyle/packagedb/ghc-{...} already exists.

To Reproduce

$ cabal init  # Use default options.
$ cabal clean
$ cabal build & cabal build

One of the two cabal builds should fail.

Expected behavior

cabal build succeeds regardless of if there are any other cabal builds running for the project.

System information

• Operating system: Ubuntu 24.04.4 LTS

$ cabal --version
cabal-install version 3.16.1.0 
compiled using version 3.16.1.0 of the Cabal library (in-tree)
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.10.3

Additional context

#11329 and #11298 seem related, but there the error is about something under the global .cabal dir, not dist-newstyle.

[isomorpheme]

After a different search query there's also #9431. I'll let maintainers decide which of all these issues can be considered duplicates.

[ulysses4ever]

#11329 and #11298 seem related, but there the error is about something under the global .cabal dir, not dist-newstyle.

#11298 is about dist-newstyle, so, yeah, I believe it's a duplicate.

Thank you for doing the search and also for raising this issue again: it helps to identify which issues out of thousands open issues on this tracker are more relevant today. Sadly, Cabal never had a robust concurrency setup, so fixing these issues may require big changes... or maybe not. We'd welcome a volunteer to dive deeper into it.