QueueUpdate(Draw) deadlocks in goroutine

[craftyguy]

I'm trying to update the text in a textview, and wrapping it in a QueueUpdate (or QueueUpdateDraw), per the wiki page on concurrency, deadlocks 100% of the time:

package main

import (
        "fmt"
        "time"

        "github.com/rivo/tview"
)

var (
        tv  *tview.TextView    = tview.NewTextView()
        app *tview.Application = tview.NewApplication()
)

func update() {
        var i int
        for {
                app.QueueUpdateDraw(func() {
                        tv.SetText(fmt.Sprintf("%d", i))
                })

                time.Sleep(1 * time.Second)
                i++
        }
}

func main() {
        go update()

        if err := tview.NewApplication().SetRoot(tv, true).EnableMouse(true).Run(); err != nil {
                panic(err)
        }
}

The wiki says I should call Application.Draw in the "changed" handler for a textview, however this does not result in the screen being updated with any changes when using SetText:

...(snipped unchanged code)...

func update() {
        var i int
        for {
                tv.SetText(fmt.Sprintf("%d", i))

                time.Sleep(400 * time.Millisecond)
                i++
        }
}

func changed() {
        app.Draw()
}

func main() {
        tv.SetChangedFunc(changed)
        go update()

...(snipped unchanged code)...

What's the correct way to update a textview from a goroutine?

I'm using Go 1.17.4 on Alpine Linux (amd64)

[darkhz]

Hello @craftyguy,
The first code snippet does not particularly deadlock for me when I tried it. The reason why the screen is not being updated is because you put your textview tv in a newly created Application:

if err := tview.NewApplication().SetRoot(tv, true).EnableMouse(true).Run(); err != nil {
                panic(err)
}

but you're using another already created Application instance (app, which was not initialized by calling Run() to begin with) to concurrently update your textview:

var app *tview.Application = tview.NewApplication()

app.QueueUpdateDraw(func() {
       tv.SetText(fmt.Sprintf("%d", i))
})

So your textview will be updated in a different Application than you originally intended. Therefore, use the same Application instance you declared before for all your UI related operations.

Here is the corrected code:

package main

import (
        "fmt"
        "time"

        "github.com/rivo/tview"
)

var (
        tv  *tview.TextView    = tview.NewTextView()
        app *tview.Application = tview.NewApplication()
)

func update() {
        var i int
        for {
                app.QueueUpdateDraw(func() {
                        tv.SetText(fmt.Sprintf("%d", i))
                })

                time.Sleep(1 * time.Second)
                i++
        }
}

func main() {
        go update()

        // Corrected here
        if err := app.SetRoot(tv, true).EnableMouse(true).Run(); err != nil {
                panic(err)
        }
}

This worked as intended when I tested it.

[craftyguy]

oof, I see the problem now. Sorry for the noise and thank you for taking the time to explain my problem :)