Invalidations caused by lock(io::IOCustom)

[sumiya11]

It seems that lock(io::IOCustom) in combination with Groebner.jl wins the first prize for the number of method invalidations.

Running

# from https://sciml.ai/news/2022/09/21/compile_time/
using SnoopCompile

invalidations = @snoopr begin
    using AbstractAlgebra
    R, (x,y) = polynomial_ring(QQ, ["x","y"], ordering=:degrevlex)
    using Groebner
    groebner([x^2 - y^2, x*y^2 + x])
end

trees = SnoopCompile.invalidation_trees(invalidations);

@show length(SnoopCompile.uinvalidated(invalidations)) # show total invalidations (1102)

show(trees[end]) # show the most invalidated method

I get

inserting lock(io::AbstractAlgebra.PrettyPrinting.IOCustom) @ AbstractAlgebra.PrettyPrinting C:\data\projects\AbstractAlgebra.jl\src\PrettyPrinting.jl:1840 invalidated:
   backedges: 1: superseding lock(::IO) @ Base io.jl:26 with MethodInstance for lock(::IO) (621 children)
              2: superseding lock(::IO) @ Base io.jl:26 with MethodInstance for lock(::IO) (4 children)

This is more than half of the total number of invalidated methods. I use AbstractAlgebra.jl from the master branch, but the issue seems to be present also for older versions.

At the moment, I am not sure why this happens, or how to fix this. Looks related: JuliaLang/julia#46878

[fingolfin]

You don't really need the "Groebner" package, just do

invalidations = @snoopr using AbstractAlgebra

and it already reports a few hundred invalidations.

However, there is nothing wrong with our lock method as far as I can tell - the culprit is most likely the code calling lock. E.g. it may not be fully type stable. You can do

ascend(trees[end].backedges[1])

to find out more. Here is a screenshot to retain the colors:

As you can see, println is the "culprit" here. It is defined like this:

println(xs...) = println(stdout, xs...)

but stdout is a non-constant global, so this code is not type stable.

So I really don't see what we could do about it; as you already found out it is really an issue in Julia itself, as you found out.

[sumiya11]

Thanks for your comment and the explanation !