gpu function does nothing, but only on first run

[clintonTE]

This isn't that big a deal, as the workarounds are fairly obvious, but it is rather strange. Note this seems very related (same root issue?) as #1114.

This is on the latest Flux Master. IDE is Windows-Juno with Julia 1.4.

using Revise, CUDAapi, Flux, BenchmarkTools
import CuArrays

struct MWEStruct{Ta<:AbstractVector, Tb<:AbstractVector}
  a::Ta
  b::Tb
end

MWEStruct(N) = MWEStruct(rand(N), rand(N))

(m::MWEStruct)(x) = x

function mwe(N)
  Flux.@functor MWEStruct

  cpustruct = MWEStruct(N)
  println("type of cpu struct: ", typeof(cpustruct))
  gpustruct = cpustruct |> gpu
  println("type of gpu struct: ", typeof(gpustruct))
end

println("First run:")
mwe(10)
println("\nSecond run:")
mwe(10)

Output:

First run:
type of cpu struct: MWEStruct{Array{Float64,1},Array{Float64,1}}
type of gpu struct: MWEStruct{Array{Float64,1},Array{Float64,1}}

Second run:
type of cpu struct: MWEStruct{Array{Float64,1},Array{Float64,1}}
type of gpu struct: MWEStruct{CuArrays.CuArray{Float32,1,Nothing},CuArrays.CuArray{Float32,1,Nothing}}

[DrChainsaw]

I believe this is because you call the functor macro inside a function. Put it somewhere outside, e.g right after the declaration of MWEStruct.

This explanation might not be 100%, but here's my understanding of it: The function it creates for you will not be available until you hit the global scope so that the world age advances which in this case is after mwe returns. Search for "world age problem julia language" for more info.