Struct Schedule

pub struct Schedule { /* private fields */ }

A collection of systems, and the metadata and executor needed to run them in a certain order under certain conditions.

Example

Here is an example of a Schedule running a “Hello world” system:

fn hello_world() { println!("Hello world!") }

fn main() {
    let mut world = World::new();
    let mut schedule = Schedule::default();
    schedule.add_systems(hello_world);

    schedule.run(&mut world);
}

A schedule can also run several systems in an ordered way:

fn system_one() { println!("System 1 works!") }
fn system_two() { println!("System 2 works!") }
fn system_three() { println!("System 3 works!") }

fn main() {
    let mut world = World::new();
    let mut schedule = Schedule::default();
    schedule.add_systems((
        system_two,
        system_one.before(system_two),
        system_three.after(system_two),
    ));

    schedule.run(&mut world);
}

Implementations

impl Schedule

pub fn new(label: impl ScheduleLabel) -> Schedule

Constructs an empty Schedule.

Examples found in repository

examples/ecs/custom_schedule.rs (line 22)

fn main() {
    let mut app = App::new();

    // Create a new [`Schedule`]. For demonstration purposes, we configure it to use a single threaded executor so that
    // systems in this schedule are never run in parallel. However, this is not a requirement for custom schedules in
    // general.
    let mut custom_update_schedule = Schedule::new(SingleThreadedUpdate);
    custom_update_schedule.set_executor_kind(ExecutorKind::SingleThreaded);

    // Adding the schedule to the app does not automatically run the schedule. This merely registers the schedule so
    // that systems can look it up using the `Schedules` resource.
    app.add_schedule(custom_update_schedule);

    // Bevy `App`s have a `main_schedule_label` field that configures which schedule is run by the App's `runner`.
    // By default, this is `Main`. The `Main` schedule is responsible for running Bevy's main schedules such as
    // `Update`, `Startup` or `Last`.
    //
    // We can configure the `Main` schedule to run our custom update schedule relative to the existing ones by modifying
    // the `MainScheduleOrder` resource.
    //
    // Note that we modify `MainScheduleOrder` directly in `main` and not in a startup system. The reason for this is
    // that the `MainScheduleOrder` cannot be modified from systems that are run as part of the `Main` schedule.
    let mut main_schedule_order = app.world_mut().resource_mut::<MainScheduleOrder>();
    main_schedule_order.insert_after(Update, SingleThreadedUpdate);

    // Adding a custom startup schedule works similarly, but needs to use `insert_startup_after`
    // instead of `insert_after`.
    app.add_schedule(Schedule::new(CustomStartup));

    let mut main_schedule_order = app.world_mut().resource_mut::<MainScheduleOrder>();
    main_schedule_order.insert_startup_after(PreStartup, CustomStartup);

    app.add_systems(SingleThreadedUpdate, single_threaded_update_system)
        .add_systems(CustomStartup, custom_startup_system)
        .add_systems(PreStartup, pre_startup_system)
        .add_systems(Startup, startup_system)
        .add_systems(First, first_system)
        .add_systems(Update, update_system)
        .add_systems(Last, last_system)
        .run();
}

pub fn label(&self) -> Interned<dyn ScheduleLabel>

Get the InternedScheduleLabel for this Schedule.

Examples found in repository

tests/ecs/ambiguity_detection.rs (line 77)

fn count_ambiguities(sub_app: &SubApp) -> AmbiguitiesCount {
    let schedules = sub_app.world().resource::<Schedules>();
    let mut ambiguities = HashMap::new();
    for (_, schedule) in schedules.iter() {
        let ambiguities_in_schedule = schedule.graph().conflicting_systems().len();
        ambiguities.insert(schedule.label(), ambiguities_in_schedule);
    }
    AmbiguitiesCount(ambiguities)
}

pub fn add_systems<M>( &mut self, systems: impl IntoSystemConfigs<M>, ) -> &mut Schedule

Add a collection of systems to the schedule.

pub fn ignore_ambiguity<M1, M2, S1, S2>( &mut self, a: S1, b: S2, ) -> &mut Schedule

where S1: IntoSystemSet<M1>, S2: IntoSystemSet<M2>,

Suppress warnings and errors that would result from systems in these sets having ambiguities (conflicting access but indeterminate order) with systems in set.

pub fn configure_sets( &mut self, sets: impl IntoSystemSetConfigs, ) -> &mut Schedule

Configures a collection of system sets in this schedule, adding them if they does not exist.

pub fn set_build_settings( &mut self, settings: ScheduleBuildSettings, ) -> &mut Schedule

Changes miscellaneous build settings.

Examples found in repository

tests/ecs/ambiguity_detection.rs (lines 62-67)

fn configure_ambiguity_detection(sub_app: &mut SubApp) {
    let mut schedules = sub_app.world_mut().resource_mut::<Schedules>();
    for (_, schedule) in schedules.iter_mut() {
        schedule.set_build_settings(ScheduleBuildSettings {
            // NOTE: you can change this to `LogLevel::Ignore` to easily see the current number of ambiguities.
            ambiguity_detection: LogLevel::Warn,
            use_shortnames: false,
            ..default()
        });
    }
}

examples/ecs/nondeterministic_system_order.rs (lines 26-29)

fn main() {
    App::new()
        // We can modify the reporting strategy for system execution order ambiguities on a per-schedule basis.
        // You must do this for each schedule you want to inspect; child schedules executed within an inspected
        // schedule do not inherit this modification.
        .edit_schedule(Update, |schedule| {
            schedule.set_build_settings(ScheduleBuildSettings {
                ambiguity_detection: LogLevel::Warn,
                ..default()
            });
        })
        .init_resource::<A>()
        .init_resource::<B>()
        .add_systems(
            Update,
            (
                // This pair of systems has an ambiguous order,
                // as their data access conflicts, and there's no order between them.
                reads_a,
                writes_a,
                // This pair of systems has conflicting data access,
                // but it's resolved with an explicit ordering:
                // the .after relationship here means that we will always double after adding.
                adds_one_to_b,
                doubles_b.after(adds_one_to_b),
                // This system isn't ambiguous with adds_one_to_b,
                // due to the transitive ordering created by our constraints:
                // if A is before B is before C, then A must be before C as well.
                reads_b.after(doubles_b),
                // This system will conflict with all of our writing systems
                // but we've silenced its ambiguity with adds_one_to_b.
                // This should only be done in the case of clear false positives:
                // leave a comment in your code justifying the decision!
                reads_a_and_b.ambiguous_with(adds_one_to_b),
            ),
        )
        // Be mindful, internal ambiguities are reported too!
        // If there are any ambiguities due solely to DefaultPlugins,
        // or between DefaultPlugins and any of your third party plugins,
        // please file a bug with the repo responsible!
        // Only *you* can prevent nondeterministic bugs due to greedy parallelism.
        .add_plugins(DefaultPlugins)
        .run();
}

pub fn get_build_settings(&self) -> ScheduleBuildSettings

Returns the schedule’s current ScheduleBuildSettings.

pub fn get_executor_kind(&self) -> ExecutorKind

Returns the schedule’s current execution strategy.

pub fn set_executor_kind(&mut self, executor: ExecutorKind) -> &mut Schedule

Sets the schedule’s execution strategy.

Examples found in repository

examples/ecs/custom_schedule.rs (line 23)

fn main() {
    let mut app = App::new();

    // Create a new [`Schedule`]. For demonstration purposes, we configure it to use a single threaded executor so that
    // systems in this schedule are never run in parallel. However, this is not a requirement for custom schedules in
    // general.
    let mut custom_update_schedule = Schedule::new(SingleThreadedUpdate);
    custom_update_schedule.set_executor_kind(ExecutorKind::SingleThreaded);

    // Adding the schedule to the app does not automatically run the schedule. This merely registers the schedule so
    // that systems can look it up using the `Schedules` resource.
    app.add_schedule(custom_update_schedule);

    // Bevy `App`s have a `main_schedule_label` field that configures which schedule is run by the App's `runner`.
    // By default, this is `Main`. The `Main` schedule is responsible for running Bevy's main schedules such as
    // `Update`, `Startup` or `Last`.
    //
    // We can configure the `Main` schedule to run our custom update schedule relative to the existing ones by modifying
    // the `MainScheduleOrder` resource.
    //
    // Note that we modify `MainScheduleOrder` directly in `main` and not in a startup system. The reason for this is
    // that the `MainScheduleOrder` cannot be modified from systems that are run as part of the `Main` schedule.
    let mut main_schedule_order = app.world_mut().resource_mut::<MainScheduleOrder>();
    main_schedule_order.insert_after(Update, SingleThreadedUpdate);

    // Adding a custom startup schedule works similarly, but needs to use `insert_startup_after`
    // instead of `insert_after`.
    app.add_schedule(Schedule::new(CustomStartup));

    let mut main_schedule_order = app.world_mut().resource_mut::<MainScheduleOrder>();
    main_schedule_order.insert_startup_after(PreStartup, CustomStartup);

    app.add_systems(SingleThreadedUpdate, single_threaded_update_system)
        .add_systems(CustomStartup, custom_startup_system)
        .add_systems(PreStartup, pre_startup_system)
        .add_systems(Startup, startup_system)
        .add_systems(First, first_system)
        .add_systems(Update, update_system)
        .add_systems(Last, last_system)
        .run();
}

pub fn set_apply_final_deferred( &mut self, apply_final_deferred: bool, ) -> &mut Schedule

Set whether the schedule applies deferred system buffers on final time or not. This is a catch-all in case a system uses commands but was not explicitly ordered before an instance of apply_deferred. By default this setting is true, but may be disabled if needed.

pub fn run(&mut self, world: &mut World)

Runs all systems in this schedule on the world, using its current execution strategy.

pub fn initialize( &mut self, world: &mut World, ) -> Result<(), ScheduleBuildError>

Initializes any newly-added systems and conditions, rebuilds the executable schedule, and re-initializes the executor.

Moves all systems and run conditions out of the ScheduleGraph.

pub fn graph(&self) -> &ScheduleGraph

Returns the ScheduleGraph.

Examples found in repository

tests/ecs/ambiguity_detection.rs (line 76)

fn count_ambiguities(sub_app: &SubApp) -> AmbiguitiesCount {
    let schedules = sub_app.world().resource::<Schedules>();
    let mut ambiguities = HashMap::new();
    for (_, schedule) in schedules.iter() {
        let ambiguities_in_schedule = schedule.graph().conflicting_systems().len();
        ambiguities.insert(schedule.label(), ambiguities_in_schedule);
    }
    AmbiguitiesCount(ambiguities)
}

pub fn graph_mut(&mut self) -> &mut ScheduleGraph

Returns a mutable reference to the ScheduleGraph.

pub fn apply_deferred(&mut self, world: &mut World)

Directly applies any accumulated Deferred system parameters (like Commands) to the world.

Like always, deferred system parameters are applied in the “topological sort order” of the schedule graph. As a result, buffers from one system are only guaranteed to be applied before those of other systems if there is an explicit system ordering between the two systems.

This is used in rendering to extract data from the main world, storing the data in system buffers, before applying their buffers in a different world.

pub fn systems( &self, ) -> Result<impl Iterator<Item = (NodeId, &Box<dyn System<In = (), Out = ()>>)>, ScheduleNotInitialized>

Returns an iterator over all systems in this schedule.

Note: this method will return ScheduleNotInitialized if the schedule has never been initialized or run.

Examples found in repository

examples/games/stepping.rs (line 128)

fn build_ui(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    schedules: Res<Schedules>,
    mut stepping: ResMut<Stepping>,
    mut state: ResMut<State>,
) {
    let mut text_spans = Vec::new();
    let mut always_run = Vec::new();

    let Ok(schedule_order) = stepping.schedules() else {
        return;
    };

    // go through the stepping schedules and construct a list of systems for
    // each label
    for label in schedule_order {
        let schedule = schedules.get(*label).unwrap();
        text_spans.push((
            TextSpan(format!("{label:?}\n")),
            TextFont {
                font: asset_server.load(FONT_BOLD),
                ..default()
            },
            TextColor(FONT_COLOR),
        ));

        // grab the list of systems in the schedule, in the order the
        // single-threaded executor would run them.
        let Ok(systems) = schedule.systems() else {
            return;
        };

        for (node_id, system) in systems {
            // skip bevy default systems; we don't want to step those
            if system.name().starts_with("bevy") {
                always_run.push((*label, node_id));
                continue;
            }

            // Add an entry to our systems list so we can find where to draw
            // the cursor when the stepping cursor is at this system
            // we add plus 1 to account for the empty root span
            state.systems.push((*label, node_id, text_spans.len() + 1));

            // Add a text section for displaying the cursor for this system
            text_spans.push((
                TextSpan::new("   "),
                TextFont::default(),
                TextColor(FONT_COLOR),
            ));

            // add the name of the system to the ui
            text_spans.push((
                TextSpan(format!("{}\n", system.name())),
                TextFont::default(),
                TextColor(FONT_COLOR),
            ));
        }
    }

    for (label, node) in always_run.drain(..) {
        stepping.always_run_node(label, node);
    }

    commands
        .spawn((
            Text::default(),
            SteppingUi,
            Node {
                position_type: PositionType::Absolute,
                top: state.ui_top,
                left: state.ui_left,
                padding: UiRect::all(Val::Px(10.0)),
                ..default()
            },
            BackgroundColor(Color::srgba(1.0, 1.0, 1.0, 0.33)),
            Visibility::Hidden,
        ))
        .with_children(|p| {
            for span in text_spans {
                p.spawn(span);
            }
        });
}

pub fn systems_len(&self) -> usize

Returns the number of systems in this schedule.

Trait Implementations

impl Default for Schedule

fn default() -> Schedule

Creates a schedule with a default label. Only use in situations where you don’t care about the ScheduleLabel. Inserting a default schedule into the world risks overwriting another schedule. For most situations you should use Schedule::new.