GtkWindow doesn't display a new window when Gtk4 is built in a sysimage

[cmey]

Start in a fresh Julia 1.9-rc2 environment, install Gtk4 and PackageCompiler:

julia +1.9 --project=.
(Gtk4.jl-work) pkg> add Gtk4, PackageCompiler
julia> exit()

Make package compiler scripts:

cat scripts/run_package_compiler.sh
julia +1.9 --project=. scripts/run_package_compiler.jl

---

cat scripts/run_package_compiler.jl
using PackageCompiler

packages = [
    :Gtk4,
]

create_sysimage(
    packages,
    sysimage_path="sysimage.so",
    precompile_execution_file=(@__DIR__) * "/precompile_execution_file.jl")

---

cat scripts/precompile_execution_file.jl
using Gtk4
win = Gtk4.GtkWindow()

Run package compiler:

./scripts/run_package_compiler.sh

Start Julia with the newly built sysimage:

julia +1.9 --project=. --sysimage=sysimage.so

julia> using Gtk4
julia> Gtk4.GtkWindow()

Notice unexpectedly no window appears. When I don't load the sysimage, then the window appears.

This happens on:

julia> versioninfo()
Julia Version 1.9.0-rc2
Commit 72aec423c2a (2023-04-01 10:41 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin21.4.0)
  CPU: 16 × Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-14.0.6 (ORCJIT, skylake)
  Threads: 1 on 16 virtual cores

(Gtk4.jl-work) pkg> st
Status `~/Code/julia/Gtk4.jl-work/Project.toml`
  [9db2cae5] Gtk4 v0.3.4
  [9b87118b] PackageCompiler v2.1.5

[jwahlstrand]

Thanks for the detailed report. It looks like the main loop is not being started automatically. When I call Gtk4.GLib.start_main_loop() before or after creating the window, it appears and subsequent windows do too. Right now the main loop is started by default when isinteractive() == true and I guess it makes sense that this condition isn't satisfied when you create a sysimage.

This behavior deserves some discussion and documentation. The reason I did it this way was to better support GtkApplication, which wants to run the loop itself. I was thinking that GtkApplication, which lets you use actions and enables a few other things, was mainly useful for non-REPL applications. But in GTK4 they really push you to use GtkApplication; I've noticed that on Linux a lot of random warnings are spewn when you use the file chooser dialogs without it. Should we use a default GtkApplication for the REPL?

[tknopp]

Should we use a default GtkApplication for the REPL?

I am not sure what the implications would be. If this is invisible to the user, I think this could be a good approach. If one need to explicitly create the GtkApplication and call the blocking run method, we would loose this nice interactivity.

[jwahlstrand]

Yeah, agreed, I think we could make it invisible to the user. I'll look into it when I have time.

[jwahlstrand]

There is now a mention in the docs of the need to start the main loop: https://juliagtk.github.io/Gtk4.jl/dev/howto/sysimage/

On the issue of having a default GtkApplication for the REPL, I decided it would be too complicated and would probably cause trouble if multiple applications shared it.