Dropping Root outside Runtime.run panics

[Grinshpon]

In a project, I have a state struct that contains a glsp runtime and a struct that holds callbacks:

struct Callbacks {
  //various callbacks of type: Option<Root<GFn>>
}

struct State {
  callbacks: Callbacks,
  runtime: Runtime,
  ...
}

At the very end of the program, when the state is dropped, it panics with the error: a Root or Gc has outlived its originating Runtime - aborting process

I then tried manually dropping the callbacks before the end of the program, and it seems the panic occurs there, so it looks like I can't drop Roots unless I'm in a runtime environment. Is this intentional?

[fleabitdev]

Thanks for the report!

This is intentional and documented. The best way to work around it is to construct your Runtime at the very start of your main function, run it immediately, and keep running it until the very end of your main function, as documented here.

Leaving this issue open, because the rule should be documented more prominently, particularly in the rustdoc pages for Root, Gc and Val. We should probably add a more explicit warning to the-glsp-crate.md, too. This rule used to be documented alongside the GSend marker trait, but that trait was removed in version 0.2, so the documentation is currently a little sparse.

[Grinshpon]

Ah, I see, thank you!

Just curious, is there a significant performance difference in calling run once and keeping it active, versus calling it once or more each frame?

[fleabitdev]

run is basically free! It just changes the value of a thread-local Option<Rc<_>>, and then changes it back after running the closure.