Pinning GC threads

[carstenbauer]

We do have a basic API for pinning threads loosely to, e.g., NUMA domains now (issue #67, PR #71).

How to access/pin GC threads? Assuming we can't @tspawnat code on them (correct?) we likely need a low-level API in the Julia runtime, right? Similar to https://github.com/xianyi/OpenBLAS/blob/4d0b7fbec04c95c90291938a5974f00673e10e68/driver/others/blas_server.c#L341-L369 perhaps?

(cc @vchuravy)

[carstenbauer]

The new API will be in Julia 1.11: JuliaLang/julia#53402

See the related issue #95

[carstenbauer]

Beta support has landed on the main branch. However, it doesn't seem possible to pin the last GC thread somehow. We'll have to figure this out later.