segfault running webview.Eval in goroutine a lot

[Le0Developer]

Ran into this segfault when my app did an oopsie and recursively called a binding that spawned a goroutine which eval'ed itself.

package main

import (
	"fmt"

	webview "github.com/webview/webview_go"
)

func main() {
	w := webview.New(true)
	defer w.Destroy()
	w.SetTitle("Basic Example")
	w.SetSize(480, 320, webview.HintNone)
	w.SetHtml("<button onclick=\"exec()\">Click</button>")
	dept := 0
	w.Bind("exec", func() {
		go func() {
			fmt.Println("exec", dept)
			dept++
			// w.Dispatch(func() {
				w.Eval("setTimeout(window.exec, 1)")
			// })
		}()
	})
	w.Run()
}

Works

1. without go func() {
2. with w.Dispatch(func() {

Crash log:

Long log

exec 604
SIGSEGV: segmentation violation
PC=0x188041420 m=5 sigcode=2
signal arrived during cgo execution

goroutine 628 [syscall]:
runtime.cgocall(0x1049b7b30, 0x14000127ed8)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/cgocall.go:157 +0x44 fp=0x14000127ea0 sp=0x14000127e60 pc=0x10
49004c4
github.com/webview/webview_go._Cfunc_webview_eval(0x600000320000, 0x600002046f80)
        _cgo_gotypes.go:162 +0x30 fp=0x14000127ed0 sp=0x14000127ea0 pc=0x1049b5820
github.com/webview/webview_go.(*webview).Eval.func2(0x1049c0a62?, 0x1a?)
        /Users/leodev/go/pkg/mod/github.com/webview/[email protected]/webview.go:199 +0x50 fp
=0x14000127f10 sp=0x14000127ed0 pc=0x1049b6390
github.com/webview/webview_go.(*webview).Eval(0x104a0a1c8?, {0x1049c0a62?, 0x14000127fa8?})
        /Users/leodev/go/pkg/mod/github.com/webview/[email protected]/webview.go:199 +0x68 fp
=0x14000127f60 sp=0x14000127f10 pc=0x1049b62e8
main.main.func1.1()
        /Users/leodev/p/go/main.go:21 +0xb8 fp=0x14000127fd0 sp=0x14000127f60 pc=0x1049b7928
runtime.goexit()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/asm_arm64.s:1197 +0x4 fp=0x14000127fd0 sp=0x14000127fd0 pc=0x1
0495db24
created by main.main.func1 in goroutine 1
        /Users/leodev/p/go/main.go:17 +0x9c

goroutine 1 [syscall, locked to thread]:
runtime.cgocall(0x1049b7bb0, 0x14000117e58)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/cgocall.go:157 +0x44 fp=0x14000117e20 sp=0x14000117de0 pc=0x10
49004c4
github.com/webview/webview_go._Cfunc_webview_run(0x600000320000)
        _cgo_gotypes.go:233 +0x30 fp=0x14000117e50 sp=0x14000117e20 pc=0x1049b5940
github.com/webview/webview_go.(*webview).Run.func1(0x60000222c650?)
        /Users/leodev/go/pkg/mod/github.com/webview/[email protected]/webview.go:157 +0x40 fp
=0x14000117e90 sp=0x14000117e50 pc=0x1049b5e20
github.com/webview/webview_go.(*webview).Run(0x1400004a020?)
        /Users/leodev/go/pkg/mod/github.com/webview/[email protected]/webview.go:157 +0x1c fp
=0x14000117eb0 sp=0x14000117e90 pc=0x1049b5dbc
main.main()
        /Users/leodev/p/go/main.go:25 +0x16c fp=0x14000117f30 sp=0x14000117eb0 pc=0x1049b776c
runtime.main()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:267 +0x2bc fp=0x14000117fd0 sp=0x14000117f30 pc=0x1049
3157c
runtime.goexit()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/asm_arm64.s:1197 +0x4 fp=0x14000117fd0 sp=0x14000117fd0 pc=0x1
0495db24

goroutine 2 [force gc (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:398 +0xc8 fp=0x14000046f90 sp=0x14000046f70 pc=0x10493
19a8
runtime.goparkunlock(...)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:404
runtime.forcegchelper()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:322 +0xb8 fp=0x14000046fd0 sp=0x14000046f90 pc=0x10493
1838
runtime.goexit()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/asm_arm64.s:1197 +0x4 fp=0x14000046fd0 sp=0x14000046fd0 pc=0x1
0495db24
created by runtime.init.6 in goroutine 1
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:310 +0x24

goroutine 18 [GC sweep wait]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:398 +0xc8 fp=0x14000042760 sp=0x14000042740 pc=0x10493
19a8
runtime.goparkunlock(...)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:404
runtime.bgsweep(0x0?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgcsweep.go:280 +0xa0 fp=0x140000427b0 sp=0x14000042760 pc=0x1
0491eb50
runtime.gcenable.func1()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgc.go:200 +0x28 fp=0x140000427d0 sp=0x140000427b0 pc=0x104913
648
runtime.goexit()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/asm_arm64.s:1197 +0x4 fp=0x140000427d0 sp=0x140000427d0 pc=0x1
0495db24
created by runtime.gcenable in goroutine 1
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgc.go:200 +0x6c

goroutine 19 [GC scavenge wait]:
runtime.gopark(0x1400008e000?, 0x1049e4550?, 0x1?, 0x0?, 0x140000824e0?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:398 +0xc8 fp=0x14000042f50 sp=0x14000042f30 pc=0x10493
19a8
runtime.goparkunlock(...)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:404
runtime.(*scavengerState).park(0x104aa1640)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgcscavenge.go:425 +0x5c fp=0x14000042f80 sp=0x14000042f50 pc=
0x10491c3fc
runtime.bgscavenge(0x0?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgcscavenge.go:653 +0x44 fp=0x14000042fb0 sp=0x14000042f80 pc=
0x10491c954
runtime.gcenable.func2()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgc.go:201 +0x28 fp=0x14000042fd0 sp=0x14000042fb0 pc=0x104913
5e8
runtime.goexit()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/asm_arm64.s:1197 +0x4 fp=0x14000042fd0 sp=0x14000042fd0 pc=0x1
0495db24
created by runtime.gcenable in goroutine 1
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mgc.go:201 +0xac

goroutine 3 [finalizer wait]:
runtime.gopark(0x140000465c8?, 0x104996c10?, 0x0?, 0x0?, 0x1049bd990?)
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/proc.go:398 +0xc8 fp=0x14000046580 sp=0x14000046560 pc=0x10493
19a8
runtime.runfinq()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mfinal.go:193 +0x108 fp=0x140000467d0 sp=0x14000046580 pc=0x10
49126f8
runtime.goexit()
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/asm_arm64.s:1197 +0x4 fp=0x140000467d0 sp=0x140000467d0 pc=0x1
0495db24
created by runtime.createfing in goroutine 1
        /opt/homebrew/Cellar/go/1.21.6/libexec/src/runtime/mfinal.go:163 +0x80

r0      0x600001522dc0
r1      0x1d767a60e
r2      0x600001522dc0
r3      0x2
r4      0x4
r5      0xf60
r6      0x60000204c860
r7      0x0
r8      0xde9932f2dc0
r9      0xcb850001df096060
r10     0x6ae1600001522dc0
r11     0x1dec053bf
r12     0x0
r13     0x1ff800
r14     0xde9932f2dc0
r15     0xde9932f2dc0
r16     0xde9932f2dc0
r17     0x1e7cb24c8
r18     0x0
r19     0x16d522800
r20     0x600002e2e3a0
r21     0x600001522dc0
r22     0x600001522dc0
r23     0x1540802d0
r24     0x154108200
r25     0x154004200
r26     0x154100aa0
r27     0x29
r28     0x3
r29     0x16d5227f0
lr      0x18861ca3c
sp      0x16d522790
pc      0x188041420
fault   0xde9932f2dd0
exit status 2

[SteffenL]

When you use goroutines then you should use w.Dispatch() to get back onto the thread where you can interact with the underlying browser engine safely. Once you've sorted that out then feel free to give us an update if you have more issues.

[Le0Developer]

Ah, thanks.
It's not quite obvious that (to me at least) Eval is tweaking the native window as described in Dispatch.

You normally do not need to call this function, unless you want to tweak the native window.

Might benefit from some clarification.

[SteffenL]

That's a good point! We should investigate whether that comment is accurate.