REPL is unresponsive after using Gtk4

[cmey]

Hi!

Just using Gtk4 and waiting for a minute, makes the julia REPL unresponsive / super slow.

This is on julia 1.8.5 and also on 1.9-rc1 on a mac Intel, macOS Ventura 13.2.1.

I've tried 3 terminal apps: the Terminal app that comes with macOs, Warp, and the REPL in vscode - they all show the same behevior.

Detailed infos:

I start julia with julia +1.9 --project=. (from juliaup).

(Winston-work) pkg> st
Status `~/Code/julia/Winston-work/Project.toml`
  [9db2cae5] Gtk4 v0.3.2

julia> versioninfo()
Julia Version 1.9.0-rc1
Commit 3b2e0d8fbc1 (2023-03-07 07:51 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

(Side note: I've seen it happen on Windows too. And on Linux all is fine.)

[tknopp]

I am on Julia 1.8.0 and macOS 12.3.1 and have not seen this so far.

[jwahlstrand]

I have seen it on my Mac and it makes the REPL unusable after a minute or two, like @cmey said. I have not noticed this on Windows, which I use a lot more. The same thing happens for me with Gtk.jl, but only after you open a window, which starts the GLib main loop, and wait a few minutes. I noticed it goes away if I revert JuliaGraphics/Gtk.jl#630. But doing that unfortunately brings back slowdown issues with multithreading.

We could add some functions that allow you to turn uv_backend_fd integration on and off. I'd be inclined to enable it by default on Mac and Windows if isinteractive() is true. We could add a warning in the documentation that multithread performance is impacted.

[tknopp]

Hm, I have used Gtk4 on Mac quite intensively when porting a larger app and have not seen it so far. But anyways, the suggestion to make in configurable and enabling it on Mac/Windows sounds good.

[jwahlstrand]

See if what I just pushed fixes the REPL issue. It does for me.

This re-enables the uv_backend polling on a Mac if you're in an interactive session. To go back to how it was before (to prevent Gtk4 from interfering with multithreading), you can call Gtk4.set_uv_loop_integration("disabled") and then restart Julia. It uses Preferences.jl to save this setting. There are docstrings but I'll try to add some useful information about this to the documentation soon. BTW as I was working on this I realized that it's not going to fix the Windows issue, because this uv_backend polling isn't used for that platform. Not sure how to fix it there.

As I mentioned, I had seen this on my own computer (which is pretty old and slow) but figured that it wasn't an issue for everyone, since I knew @tknopp has been using Gtk4.jl on a Mac and hadn't complained.

[cmey]

@jwahlstrand Thanks a lot for the fix, I can confirm that your latest change fixes it!

I added Gtk4#main and saw no lag after playing with it for a few minutes.
I reverted to Gtk4 and got a laggy REPL almost immediately.

Can you please tag a new release with this fix? 🙏

[jwahlstrand]

Done!