ServerEvents can be missed on clients using FixedUpdate

[RJ]

because of how bevy clears event queues it currently happens that server events can fail to be received by clients using FixedUpdate.

you might write to the EventWriter, and then a few frames tick past before FixedUpdate runs again, by which time the event is long gone. Double buffering keeps it for 2 ticks only.

On your client, if you want to receive the server events in a FixedUpdate system, you might not see them all (even though replicon receives them and writes them to the EventWriter).

here (server_event.rs) is where the standard add_event is used, which is what the clients consume via a system using normal EventReaders.

to make this work for fixedupdate clients, that would need to be a manually created Events resource too, like are used for the serverside events (the ones with ToClients<> wrappers).

but then the question is: where do we clear the event queues?
we don't really know if the client is using fixedupdate..

I could change it to a manually created/cleared Events, and put a system to clear it in in Last. That would work the same for people who aren't using FixedUpdate.

Then we'd need a setting in the replicon client plugin: using_fixed_update=true which doesn't add the event clearing system, but makes the consumer add it themselves to fixedupdate.

How does that sound?

[RJ]

Here's my workaround at the moment:

fn clear_events<T: Event>(mut events: ResMut<Events<T>>) {
    events.clear();
}

fn replicon_event_setup(app: &mut App) {
    // before replicon creates these with normal `add_event`, create them manually
    // so they will not be cleared before FixedUpdate can run
    // see: https://github.com/lifescapegame/bevy_replicon/pull/85
    #[cfg(feature = "is_client")]
    {
        app.init_resource::<Events<InitClientMessage>>();
        app.init_resource::<Events<PlayerInputsMessage>>();
        app.init_resource::<Events<TimingReportMessage>>();
        app.init_resource::<Events<EventMessages>>();
        // clear them at the end of fixedupdate:
        app.add_systems(
            FixedUpdate,
            (
                clear_events::<InitClientMessage>,
                clear_events::<PlayerInputsMessage>,
                clear_events::<TimingReportMessage>,
                clear_events::<EventMessages>,
            )
                .in_set(SpacepitSet::Last),
        );
    }
    // SERVER -> CLIENT EVENTS
    app.add_server_event::<InitClientMessage>(SendPolicy::Ordered);
    app.add_server_event::<PlayerInputsMessage>(SendPolicy::Unreliable);
    app.add_server_event::<TimingReportMessage>(SendPolicy::Unreliable);
    app.add_server_event::<EventMessages>(SendPolicy::Unreliable);
    // ...
}

[UkoeHB]

For reference, this is fixed in this bevy PR.

[RJ]

Could just document the workaround until bevy solves it for us 🤷‍♂️

[Shatur]

Fixed in Bevy 0.12.1, closing.