[GH-ISSUE #339] panic: unknown tcell event type: <nil> #156

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opened 2026-03-03 16:22:57 +03:00 by kerem · 1 comment

kerem commented

2026-03-03 16:22:57 +03:00

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Originally created by @kmulvey on GitHub (Oct 14, 2022).
Original GitHub issue: https://github.com/mum4k/termdash/issues/339

I get this error every time I try to quit (by pressing 'q'). It also leaves the terminal window in an unusable state. Where do i start debugging this? The stack trace doesnt even list any of my code.

       quitter := func(k *terminalapi.Keyboard) {
           if k.Key == 'q' || k.Key == 'Q' {
               term.Close()
           }
       }

Full code is here: https://github.com/kmulvey/text2speech/blob/main/dashboard.go

panic: unknown tcell event type: <nil>

goroutine 59 [running]:
github.com/mum4k/termdash.(*termdash).handleError(...)
	/opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/termdash.go:252
github.com/mum4k/termdash.(*termdash).subscribers.func1({0xb61960?, 0xc000118010?})
	/opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/termdash.go:215 +0xd2
github.com/mum4k/termdash/private/event.(*subscriber).callback(0xc00007e2c0, {0xb61960?, 0xc000118010?})
	/opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/private/event/event.go:95 +0x31
github.com/mum4k/termdash/private/event.(*subscriber).run(0xc00007e2c0, {0xb66b18, 0xc00007e200})
	/opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/private/event/event.go:110 +0x5a
created by github.com/mum4k/termdash/private/event.newSubscriber
	/opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/private/event/event.go:89 +0x205

Originally created by @kmulvey on GitHub (Oct 14, 2022). Original GitHub issue: https://github.com/mum4k/termdash/issues/339 I get this error every time I try to quit (by pressing 'q'). It also leaves the terminal window in an unusable state. Where do i start debugging this? The stack trace doesnt even list any of my code. ``` quitter := func(k *terminalapi.Keyboard) { if k.Key == 'q' || k.Key == 'Q' { term.Close() } } ``` Full code is here: https://github.com/kmulvey/text2speech/blob/main/dashboard.go ``` panic: unknown tcell event type: <nil> goroutine 59 [running]: github.com/mum4k/termdash.(*termdash).handleError(...) /opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/termdash.go:252 github.com/mum4k/termdash.(*termdash).subscribers.func1({0xb61960?, 0xc000118010?}) /opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/termdash.go:215 +0xd2 github.com/mum4k/termdash/private/event.(*subscriber).callback(0xc00007e2c0, {0xb61960?, 0xc000118010?}) /opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/private/event/event.go:95 +0x31 github.com/mum4k/termdash/private/event.(*subscriber).run(0xc00007e2c0, {0xb66b18, 0xc00007e200}) /opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/private/event/event.go:110 +0x5a created by github.com/mum4k/termdash/private/event.newSubscriber /opt/code/go/pkg/mod/github.com/mum4k/termdash@v0.17.0/private/event/event.go:89 +0x205 ```

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2026-03-03 16:22:57 +03:00

kerem commented

2026-03-03 16:22:58 +03:00

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@mum4k commented on GitHub (Oct 18, 2022):

I think the problem here is an invalid order of termination. The implemented quitter calls term.Close() thus closing the terminal object that was given to Termdash for use. This breaks the lifetime guarantee - objects given to called functions must outlive those function calls.

What happens is that the term object shuts down and becomes invalid. But there is some concurrency that still attempts to use it via termdash, probably in one of those goroutines.

The solution is to make sure that termdash and all goroutines are correctly terminated before the term object gets closed. Termination should be done in the exact opposite order of construction.

You can look at the demos for an example of a correct termination sequence, e.g. the termdashdemo:

https://github.com/mum4k/termdash/blob/master/termdashdemo/termdashdemo.go

@mum4k commented on GitHub (Oct 18, 2022): I think the problem here is an invalid order of termination. The implemented quitter calls `term.Close()` thus closing the terminal object that was given to Termdash for use. This breaks the lifetime guarantee - objects given to called functions must outlive those function calls. What happens is that the `term` object shuts down and becomes invalid. But there is some concurrency that still attempts to use it via termdash, probably in one of those goroutines. The solution is to make sure that termdash and all goroutines are correctly terminated **before** the `term` object gets closed. Termination should be done in the exact opposite order of construction. You can look at the demos for an example of a correct termination sequence, e.g. the `termdashdemo`: https://github.com/mum4k/termdash/blob/master/termdashdemo/termdashdemo.go

kerem referenced this issue

2026-03-03 16:23:24 +03:00

[PR #157] [MERGED] Moving fakewidget to the internal subdirectory. #225