goroutine crash silently

[Alain Gilbert]

Any idea how we could make a crash in a goroutine stop the VM ?
eg:

time = import("time")
for {
  go func() {
    println("before")
    This should stop the VM
    println("will never print")
  }()
  time.Sleep(time.Second)
}

This program will not crash and will just keep running as if everything is fine.
It would be nice to stop the VM in such case, and get back the error.

My workaround right now is to define a Go function

ctx, cancel := context.WithCancel(context.Background())

_ = myvm.Define("Go", func(fn func()) {
  go func() {
    defer func() {
      if r := recover(); r != nil {
        println(r)
        cancel()
      }
    }()
    fn()
  }()
})

myscript := `
time = import("time")
for {
  Go(func() {
    println("before")
    This will stop the VM
    println("will never print")
  })
  time.Sleep(time.Second)
}`

myvm.ExecuteContext(ctx, myscript)

But I have to edit the original anko code to prevent the use of the go keyword.

[MichaelS11]

The below code gives me a syntax error.

time = import("time")
for (i = 0; i < 10; i++) {
	go func() {
		println("before")
		This should stop the VM
		println("will never print")
	}()
	time.Sleep(time.Second)
}

[Alain Gilbert]

Must be something that was fixed in more recent version.

But here is another example that is broken in the current playground:
This one will stop the VM with a undefined symbol 'a' error.
http://play-anko.appspot.com/p/cafefad589d3b20b61b8055c487ef64c03aad32d
VS
This one works just fine, even though it uses undefined symbol (and that the goroutine crash)
http://play-anko.appspot.com/p/a6bca82496c93aa8b42790e21bc07b57bb681180

[MichaelS11]

For me, this:

time = import("time")
for i = 0; i < 3; i++ {
	go func() {
		println("before")
		println("will never print")
	}()
	time.Sleep(time.Second)
	println(a.b.c)
}
println("done")

Outputs:

before
will never print
2020/03/02 14:16:02 Execute error: undefined symbol 'a'

The playground may not be an up to date version.

[Alain Gilbert]

This is the correct output.

The second one is

before
before
before
done

(while it should stop after the first before)

[MichaelS11]

For me, this:

time = import("time")
for i = 0; i < 3; i++ {
	go func() {
		println("before")
		println(a.b.c)
		println("will never print")
	}()
	time.Sleep(time.Second)
}
println("done")

Also outputs:

before
before
before
done

Which is correct. Anko will not crash/stop on go function error.

[MichaelS11]

Let's stick with go func for the moment, can look at try next.

I am not sure what you mean about looping forever, the go func stops after the error.

Example:

time = import("time")
go func() {
	for i = 0; i < 3; i++ {
		println("a1")
		println(a)
		println("a2")
	}
}()
time.Sleep(time.Second)
println("done")

Output:

a1
done

[Alain Gilbert]

Sorry I deleted my comment after a few seconds, seeing the example wasn't good.

Indeed, it doesn't stop. But it should stop.
This is invalid code.
And the goroutine actually crash.
And you will never know it crashed.
This is just as good as a `try catch ignore` (which is no good at all).
Let me show you how bad this could be:

\`\`\`go
go func() {
    for {
        println("I'm going to do something every second")
        doSomething()
        time.Sleep(time.Second)
    }
}()
<-WaitForeverChan
\`\`\`
This is supposed to do something every second, but instead, it will fill your hard drive with useless logs at an insane rate because it will loop forever without executing the Sleep.

[Alain Gilbert]

but in any way, you see that the script is supposed to do something, and it won't do anything as the thread is dead, and you get no feedback whatsoever.

[MichaelS11]

As I said, Anko will not crash/stop on go func error.

[MichaelS11]

@alaingilbert So can you close this? Or is there something else?

[Alain Gilbert]

This is major flaw if you ask me. But sure, feel free to just close it if you don't plan to improve it.

[MichaelS11]

All depends on how you look at it. Can also look at it a major feature. People may like it so the whole program does not crash. Plus if you do want the whole VM to end, you have shown it can be done by using a function.

[Alain Gilbert]

So you're telling me that people want their goroutine to just crash and give no feedback ?
I would expect the same kind of behavior on the main thread. I think the app should never ever crash, and never return an error at all.

[Alain Gilbert]

Alright I'll stop here. This is not sane for any of us.
Thanks for the good work you're doing.