The crate layout itself is a bit non-standard, where lib.rs lives in the root instead of under /src. Looks like it was changed in an appropriately named PR: Cleanup and other bikeshedding.
Is the idea that because this library is self-contained you can easily compile it sans-cargo like rustc --crate-type lib ./lib.rs? That’s also true of None of the other libraries mentioned under Similar libraries have this constraint though. They can all be build with a simple scoped-threadpool-rs, but not of crossbeam.rustc invocation. I still think it’s a nice feature though.