Inconsistent allocation with threads and function arguments in 1.12

[lmiq]

Maybe this is related and a workaround:

Type-instability because of @threads boxing variables

Yes. You could try adding let blocks. Note that Threads.@spawn has sugar where using $ on variables automatically creates let blocks for you: julia> @macroexpand Threads.@spawn foo($x) quote #= threadingconstructs.jl:229 =# let var"##394" = x #= threadingconstructs.jl:230 =# local var"#14#task" = Base.Threads.Task((()->begin #= threadingconstructs.jl:226 =# foo(var"##394") end)) #= …