reduce duplicated code

[brody4hire]

While working on PR #260, I noticed what looks like quite a bit of duplicated code. I am wondering if we could find some kind of idiomatic way to make some generic structures & functions to help reduce the amount of duplicated code. I would love to take a look into this at some point.

[matklad]

Perhaps we could reduce duplication indeed, but a hard requirement here is to also simplify the code along the way. Between duplication and more complex code, I would prefer duplication.

[briansmith]

My experience with the race module was that I wanted to vendor OnceNonZeroUsize but not the rest of the file. I believe that OnceNonZeroUsize could be put into a separate submodule and then the rest of the file could be written in terms of its public API. Besides making vendoring parts easier, it would also better encapsulate the use of atomics by using a module boundary to hide the inner parts of OnceNonZeroUsize from the things that are built on top of it.