8ace2ff9e3
# Objective Scheduling low cost systems has significant overhead due to task pool contention and the extra machinery to schedule and run them. Event update systems are the prime example of a low cost system, requiring a guaranteed O(1) operation, and there are a *lot* of them. ## Solution Add a run condition to every event system so they only run when there is an event in either of it's two internal Vecs. --- ## Changelog Changed: Event update systems will not run if there are no events to process. ## Migration Guide `Events<T>::update_system` has been split off from the the type and can be found at `bevy_ecs::event::event_update_system`. --------- Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
62 lines
2.0 KiB
Rust
62 lines
2.0 KiB
Rust
use bevy_ecs::prelude::*;
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// In this example a system sends a custom event with a 50/50 chance during any frame.
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// If an event was send, it will be printed by the console in a receiving system.
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fn main() {
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// Create a new empty world and add the event as a resource
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let mut world = World::new();
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world.insert_resource(Events::<MyEvent>::default());
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// Create a schedule to store our systems
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let mut schedule = Schedule::default();
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// Events need to be updated in every frame in order to clear our buffers.
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// This update should happen before we use the events.
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// Here, we use system sets to control the ordering.
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#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
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pub struct FlushEvents;
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schedule.add_systems(bevy_ecs::event::event_update_system::<MyEvent>.in_set(FlushEvents));
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// Add systems sending and receiving events after the events are flushed.
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schedule.add_systems((
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sending_system.after(FlushEvents),
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receiving_system.after(sending_system),
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));
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// Simulate 10 frames of our world
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for iteration in 1..=10 {
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println!("Simulating frame {iteration}/10");
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schedule.run(&mut world);
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}
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}
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// This is our event that we will send and receive in systems
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#[derive(Event)]
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struct MyEvent {
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pub message: String,
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pub random_value: f32,
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}
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// In every frame we will send an event with a 50/50 chance
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fn sending_system(mut event_writer: EventWriter<MyEvent>) {
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let random_value: f32 = rand::random();
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if random_value > 0.5 {
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event_writer.send(MyEvent {
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message: "A random event with value > 0.5".to_string(),
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random_value,
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});
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}
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}
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// This system listens for events of the type MyEvent
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// If an event is received it will be printed to the console
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fn receiving_system(mut event_reader: EventReader<MyEvent>) {
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for my_event in event_reader.read() {
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println!(
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" Received message {:?}, with random value of {}",
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my_event.message, my_event.random_value
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);
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}
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}
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