Program crash: GC destroys an object unexpectedly

[jfondren]

On Tuesday, 21 September 2021 at 20:17:15 UTC, eugene wrote:
> Now, change operation order in the main like this:
>
> ```d
> void main(string[] args) {
>
>     auto Main = new Main();
>     auto stopper = new Stopper();
>
>     Main.run();
>     stopper.run();
> ```
>
> ```
> d-lang/edsm-in-d-simple-example-2 $ ./test | grep STOPPER
> 'STOPPER' registered 5 (esrc.Signal)
> 'STOPPER' registered 6 (esrc.Signal)
> 'STOPPER @ INIT' got 'M0' from 'SELF'
> 'STOPPER' enabled 5 (esrc.Signal)
> 'STOPPER' enabled 6 (esrc.Signal)
> ```
>
> Everything is Ok now,

I don't think this is reliably OK. If you're not using Stopper 
later in the function, and if there are no other references to 
it, then the GC can collect it. It just has no obligation to 
collect it, so minor differences like this might prevent that 
from happening for particular compilers/options/versions.

C# and Go have 'keepalive' functions to avoid similar behavior, 
and Java's just as aggressive about potential collection. It's 
just something that mostly doesn't matter until it becomes an 
incredibly weird bug with code like yours.