Option to pin GC threads

[carstenbauer]

I would like to add the ability to pin GC threads to ThreadPinning.jl. AFAICS, we (a user) can't run Julia code on GC threads. Hence, I think we need to add something like https://github.com/OpenMathLib/OpenBLAS/blob/4d0b7fbec04c95c90291938a5974f00673e10e68/driver/others/blas_server.c#L341-L369 to the C runtime.

Would it be possible/accepted to add such functions?

(cc @vchuravy)

PS: IIUC, we can't add this retrospectively to 1.10 but it would be great to get it into 1.11.

[carstenbauer]

Because I'm giving a Julia course at UCL this week, I couldn't implement this before 1.11 feature freeze (today), which is a bit sad. If I implement this next week, is there any chance that we can still get this into 1.11?

[gbaraldi]

I believe so, if the code isn't super complex (I don't believe it would be)

[carstenbauer]

I'm trying to implement this but I have a problem. AFAICS, we don't seem to store the thread handles (uv_thread_t uvtid) of any of the threads, which I'd like to use for uv_thread_setaffinity and uv_thread_getaffinity calls later on.

Note that OpenBLAS stores these handles and it was thus pretty easy to add affinity functions, e.g. https://github.com/OpenMathLib/OpenBLAS/pull/3702/files#diff-2b77a530a65c94d60feb21d4ce2093df0a2bd3cb710d2dc82bab32f18e1c963a.

Should I add a new storage for them or is there a different/better way to get the handles? (@gbaraldi)

[carstenbauer]

Note to self: Ok, seems like we are storing the information in the TLS (specifically, in the field system_id). Guess I have to figure out now how to query the information from jl_all_tls_states. I guess via jl_atomic_load_relaxed?