[libcxx-commits] [libcxx] [libc++] Adds shared resource helper. (PR #72529)

[Louis Dionne via libcxx-commits]

ldionne wrote:

> This abstraction is scary & heavy weight. Why do we need a generic version of it?
> 
> I wouldn't be comfortable proceeding with this change until I understand where and how it's going to be used, and I see it used in real code. I'm very uncomfortable adding utility code without users.
> 
> I don't need this change to contain the changes which use it, but I would like to see it before this proceeds.

This is to refactor `<syncstream>`, which uses a specialized version of this. We discussed this generalization in the `<syncstream>` review (https://reviews.llvm.org/D67086)

https://github.com/llvm/llvm-project/pull/72529