Recovery from panic in game loop

[erexo]

Currently I'm facing a strange bug in production that occurs very randomly and to random people. My strategy was to recover from panic and to log given message, but the problem is that the ebiten.Run() function is staging an internal goroutine for the loop, so I cant really catch given panic outside of that goroutine. It would be really helpful to recover a panic of that goroutine and throw it back in the actual method, or return that panic as an error.

package main

import (
    "log"

    "github.com/hajimehoshi/ebiten/v2"
)

func main() {
    defer func() {
        if r := recover(); r != nil {
            // r will always be nil here
            log.Println(r)
        }
    }()
    if err := ebiten.RunGame(&game{}); err != nil {
        // err will be nil as well
        log.Println(err)
    }
}

type game struct{}

func (g *game) Update() error { return nil }

func (g *game) Draw(screen *ebiten.Image) {
    _ = []int{}[0]
}

func (g *game) Layout(outsideWidth, outsideHeight int) (int, int) {
    return outsideWidth, outsideHeight
}

[hajimehoshi]

What panic is happening? Is this in Ebitengine or in your game?

[erexo]

What panic is happening?

This is the case, I have no idea and I would like to know, hence this Issue was created 😄

The panic is probably somewhere in the code, something like given example. The main problem is that, as I mentioned, it happens randomly and to random people so I cant really debug it to find out, I want to have it logged to a file so I could ask those people to send me their log files, but I can't log it because I can't recover from an internal goroutine

[hajimehoshi]

I think you should catch the log in all of your game's goroutines first.

[hajimehoshi]

Unfortunately there is no way to recover a panic in a different goroutine. This is Go's restriction, and there is nothing we can do in Ebitengine.

[erexo]

You can catch it in the actual loop goroutine...

[erexo]

did you read the example I wrote? Ebitengine offers me no tool to actually know that the Draw method panicked...

[hajimehoshi]

did you read the example I wrote? Ebitengine offers me no tool to actually know that the Draw method panicked...

What about recovering the panic in Draw?

[erexo]

and that might be the solution, thanks