SIGSEGV: segmentation violation when using a go routine inside gtk.DropTarget.Connect

[SnoutBug]

I wanted to start a somewhat heavy task (counting files in directories recursively) after the user dropped the directory onto a DropTarget.

For that I use the following code in order for the GUI not to lock up: (for simplicity I hard coded the path for now)

drop.Connect("drop", func(drop *gtk.DropTarget, src *coreglib.Value, x, y float64) {
    go func() {
    numberOfFiles := readDir("/home/me")
    lbl.SetText(fmt.Sprintf("Found %s files", numberOfFiles))
    }()
})

The code for readDir, or simply filepath.Walk

func readDir(url string) uint32 {
    var numberOfFiles uint32

    files, _ := os.ReadDir(url)
    path, _ := filepath.Abs(url)
    for _, f := range files {
        if !f.IsDir() {
            numberOfFiles += 1
        } else {
            numberOfFiles += readDir(filepath.Join(path, f.Name()))
        }
    }
    return numberOfFiles
}

For testing purposes I plugged the code into the dragndrop example you provided. After execution the program will sometimes, but not always crash with:

SIGSEGV: segmentation violation
PC=0x7f48017b8f8c m=5 sigcode=1
signal arrived during cgo execution

goroutine 5 [syscall]:
runtime.cgocall(0x75e2e0, 0xc0000525e0)
    /usr/lib/golang/src/runtime/cgocall.go:157 +0x4b fp=0xc0000525b8 sp=0xc000052580 pc=0x4cd64b
github.com/diamondburned/gotk4/pkg/core/glib._Cfunc__g_is_value(0x144a140)
    _cgo_gotypes.go:970 +0x47 fp=0xc0000525e0 sp=0xc0000525b8 pc=0x594c67
github.com/diamondburned/gotk4/pkg/core/glib.(*value).isValue(...)
    /home/me/go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.6-0.20231227124334-d08a1ac493a4/core/glib/glib.go:971
github.com/diamondburned/gotk4/pkg/core/glib.(*value).unset(0xc00048dfc0)
    /home/me/go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.6-0.20231227124334-d08a1ac493a4/core/glib/glib.go:964 +0x1f fp=0xc000052600 sp=0xc0000525e0 pc=0x59a29f
runtime.call16(0x0, 0x9feec0, 0xc0000a2000, 0x10, 0x10, 0x10, 0xc0000526c0)
    /usr/lib/golang/src/runtime/asm_amd64.s:747 +0x43 fp=0xc000052620 sp=0xc000052600 pc=0x52bf23
runtime.runfinq()
    /usr/lib/golang/src/runtime/mfinal.go:255 +0x3e7 fp=0xc0000527e0 sp=0xc000052620 pc=0x4e0147
runtime.goexit()
    /usr/lib/golang/src/runtime/asm_amd64.s:1650 +0x1 fp=0xc0000527e8 sp=0xc0000527e0 pc=0x52d9c1
created by runtime.createfing in goroutine 1
    /usr/lib/golang/src/runtime/mfinal.go:163 +0x3d

goroutine 1 [syscall, locked to thread]:
runtime.cgocall(0x776ff0, 0xc00017ddd8)
    /usr/lib/golang/src/runtime/cgocall.go:157 +0x4b fp=0xc00017ddb0 sp=0xc00017dd78 pc=0x4cd64b
github.com/diamondburned/gotk4/pkg/gio/v2._Cfunc_g_application_run(0x139e1d0, 0x1, 0x139fbb0)
    _cgo_gotypes.go:13789 +0x4b fp=0xc00017ddd8 sp=0xc00017ddb0 pc=0x5b560b
github.com/diamondburned/gotk4/pkg/gio/v2.(*Application).Run.func3(0xc00017f690?, 0x25?, 0x139fbb0?)
    /home/me/go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.6-0.20231227124334-d08a1ac493a4/gio/v2/gio.go:41611 +0x67 fp=0xc00017de20 sp=0xc00017ddd8 pc=0x5d3607
github.com/diamondburned/gotk4/pkg/gio/v2.(*Application).Run(0xc0001ad470, {0xc000016060?, 0x1, 0x1})
    /home/me/go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.6-0.20231227124334-d08a1ac493a4/gio/v2/gio.go:41611 +0x20b fp=0xc00017dee8 sp=0xc00017de20 pc=0x5d34eb
main.main()
    /home/me/git/gotk4-examples/gtk4/dragndrop/main.go:22 +0xad fp=0xc00017df40 sp=0xc00017dee8 pc=0x75d7ad
runtime.main()
    /usr/lib/golang/src/runtime/proc.go:267 +0x2bb fp=0xc00017dfe0 sp=0xc00017df40 pc=0x500f1b
runtime.goexit()
    /usr/lib/golang/src/runtime/asm_amd64.s:1650 +0x1 fp=0xc00017dfe8 sp=0xc00017dfe0 pc=0x52d9c1

[...]

Is this a bug or am I approaching this issue the wrong way?

[diamondburned]

This code has a race condition: all calls to GTK widgets (lbl.SetText in this case) must be synchronized with glib.IdleAdd, like so:

go func() {
  // blocking call...
  glib.IdleAdd(func() { label.SetText(...) })
}()

Also, prefer using ConnectDrop(...) over Connect("drop", ...).

[SnoutBug]

I think this issue need to be reopened. That does not seem to work.

The app crashed regardless no matter if I used glib.IdleAdd(...) or not. Additionally the app also crashed when I didn't set the label in the go routine. I also tried to include readDir(...) inside glib.IdleAdd(...) which did not work either (that also locks the UI which I wanted to avoid). The app always crashed with the same error.

ConnectDrop(...) does not work as mentioned in #107.

The culprit seems to be os.ReadDir(...): If I put

for {
     os.ReadDir("/home/me")
}

inside either glib.IdleAdd(...) or the go routine directly, the program will crash eventually. It seems like you need to hit the right timing, though.

[diamondburned]

What version of gotk4/pkg are you on? Can you try v0.1.0?

[diamondburned]

Whoops, I put the wrong issue number in there.

[diamondburned]

ConnectDrop should work now, but the latest commit will also include commit 96fbd78af598f729089e8165fc68bed3abb2683e which is a very unstable/experimental commit that I'm not confident will be stable.

If you see any crashes occuring at package intern, please make an issue.

[SnoutBug]

What version of gotk4/pkg are you on?

I think I was on @0.0.6 if I am not mistaken.

Can you try v0.1.0?

I tried @0.1.0 with no success, the app would crash regardless.

I also tried the @4 branch directly, allowing me to use ConnectDrop(...) which worked flawlessly with the go routine, as far as I could tell. However, Connect("drop"...) still did not work.

[diamondburned]

However, Connect("drop"...) still did not work.

This is acceptable. Connect("x") should ideally never be used. I'm only keeping it around just in case it's necessary for some reason.

[SnoutBug]

That works fine for me. Since I can now use the alternative I consider this issue resolved. Thanks a bunch for your help :)