App is crashing because of a textView

[inmylo]

My application has a textView, which is being updated very often, for example each millisecond. It sometimes crashes when I try to close a modal window with app.SetRoot(pages, true). I've figured out, that textview.go's t.buffer is sometimes empty, so I tried to add an additional check and it seems to help. You can choose a more efficient way if such exists.

Created a PR #562

Some time ago I got a similar error at the line 826 str := t.buffer[line.Line][line.Pos:line.NextPos] - maybe it should be fixed too.

Panic's error:

panic: runtime error: index out of range [1] with length 0 [recovered]
	panic: runtime error: index out of range [1] with length 0

goroutine 1 [running]:
github.com/rivo/tview.(*Application).Run.func1(0xc00015e000)
	/path/src/github.com/rivo/tview/application.go:243 +0x87
panic(0x5916e0, 0xc0001b40c0)
	/path/src/runtime/panic.go:969 +0x1b9
github.com/rivo/tview.(*TextView).Draw(0xc000152300, 0x5da440, 0xc0000d6600)
	/path/src/github.com/rivo/tview/textview.go:947 +0xded
github.com/rivo/tview.(*Grid).Draw(0xc000162090, 0x5da440, 0xc0000d6600)
	/path/src/github.com/rivo/tview/grid.go:626 +0x12cf
github.com/rivo/tview.(*Pages).Draw(0xc00009ad80, 0x5da440, 0xc0000d6600)
	/path/src/github.com/rivo/tview/pages.go:277 +0xb9
github.com/rivo/tview.(*Application).draw(0xc00015e000, 0x0)
	/path/src/github.com/rivo/tview/application.go:595 +0xd9
github.com/rivo/tview.(*Application).Run(0xc00015e000, 0x0, 0x0)
	/path/src/github.com/rivo/tview/application.go:343 +0x625
main.main()
	/path/src/github.com/user/myapp/main.go:43 +0x88
exit status 2

[rivo]

How do you update the TextView's content? Do you write to it using the io.Writer interface or do you call SetText() on it?

[inmylo]

Currently I do it this way:

go func() {
	for {
		widget.SetText(text)
		app.Draw()
		time.Sleep(32 * time.Millisecond)
	}
}()

But I'm not sure whether I have to call Draw() every iteration, but it also seems to help to prevent crashing. Maybe it can be avoided to decrease CPU load

[rivo]

When you call app.Draw(), it will not redraw immediately but queue a redraw request to be completed at the next possible opportunity (from within the main loop). Doing this every 32 milliseconds might lead that request queue to become too big if the loop can't keep up.

Also, the SetText() function is not thread-safe and shouldn't be called in a non-main goroutine.

I would suggest that you rather do something like this:

go func() {
	for {
		app.QueueUpdateDraw(func() {
			textView.SetText(text)
		})
	}
}()

If you still get crashes with this code, please post some (short) code that reproduces that issue so I can get to the root of it.