Anybody Have a Simple Deterministic Bevy Stage?

[zicklag]

Hey there! I'm making a game that uses a p2p rollback networking model and I'm having an issue because of the non-deterministic system order.

There are a set of systems, the ones for handling item spawning in my game, that I really don't care what order they run in, but I need to make sure that they always run in the same order, whatever that order is.

I'm also fine running them single-threaded.

Does anybody have a simple implementation of the Stage trait that works like that?

I could alternatively add explicit ordering between my systems, but that's annoying because I am going to have a growing list of items, all in different files, and trying to put an explicit ordering between them is going to be error prone as we add more items, especially when I really don't care what order they run in, just that it doesn't change between different executions of the game.

[hymm]

does SystemStage::single_threaded work for your use case?https://docs.rs/bevy/latest/bevy/ecs/prelude/struct.SystemStage.html#method.single_threaded

[hymm]

I suppose not since it doesn't guarantee system ordering.

[zicklag]

Yeah, that's the issue. Even though they'll run the same every time once the game starts, different runs of the game could have a different order.

[hymm]

An old version of the executor ran systems in insertion order. Not sure if it would be possible to use that or not.

[james7132]

Stageless should introduce a utility for setting up strict linear ordering of systems. In the meantime, #2381 detailed an API for tighter control over system ordering, which has been forked off into the bevy_system_graph ecosystem crate.

[hymm]

Can you use bevy_system_graph to order between plugins?

[zicklag]

Very nifty @james7132, thanks for the link! That will work for me.

I'm already using some extension traits to make working with my custom rollback Schedule easier across plugins so I can do something similar to make the SystemGraph work.

[james7132]

Can you use bevy_system_graph to order between plugins?

No, but you already have labels for those, and it's not mutually exclusive with them.