Replace App::update() to World::run_schedule()

Moved the responsibility for running top-level schedules
from `App` struct to the runner function.

benches/benches/bevy_ecs/scheduling/schedule.rs

@@ -85,7 +85,7 @@ pub fn build_schedule(criterion: &mut Criterion) {
                 for _ in 0..graph_size {
                     app.add_systems(Update, empty_system);
                 }
-                app.update();
+                app.world.run_schedule(Update);
             });
         });
 
@@ -111,7 +111,7 @@ pub fn build_schedule(criterion: &mut Criterion) {
                 // This is necessary since dependency resolution does not occur until the game runs.
                 // FIXME: Running the game clutters up the benchmarks, so ideally we'd be
                 // able to benchmark the dependency resolution directly.
-                app.update();
+                app.world.run_schedule(Update);
             });
         });
     }

crates/bevy_app/src/app.rs

@@ -64,13 +64,12 @@ pub struct App {
     /// the application's event loop and advancing the [`Schedule`].
     /// Typically, it is not configured manually, but set by one of Bevy's built-in plugins.
     /// See `bevy::winit::WinitPlugin` and [`ScheduleRunnerPlugin`](crate::schedule_runner::ScheduleRunnerPlugin).
-    pub runner: Box<dyn FnOnce(App) + Send + Sync>,
-    /// The schedule that systems are added to by default.
     ///
-    /// The schedule that runs the main loop of schedule execution.
+    /// # Note
     ///
-    /// This is initially set to [`Main`].
-    pub main_schedule_label: BoxedScheduleLabel,
+    /// Inside the runner function, `World::clear_trackers()` must be called periodically.
+    /// If that isn't called on a world, it may lead to memory leaks in `RemovedComponents`.
+    pub runner: Box<dyn FnOnce(App) + Send + Sync>,
     sub_apps: HashMap<AppLabelId, SubApp>,
     plugin_registry: Vec<Box<dyn Plugin>>,
     plugin_name_added: HashSet<String>,
@@ -135,6 +134,11 @@ pub struct SubApp {
     /// The [`SubApp`]'s instance of [`App`]
     pub app: App,
 
+    /// The schedule to run by default.
+    ///
+    /// This is initially set to [`Main`].
+    pub main_schedule_label: BoxedScheduleLabel,
+
     /// A function that allows access to both the main [`App`] [`World`] and the [`SubApp`]. This is
     /// useful for moving data between the sub app and the main app.
     extract: Box<dyn Fn(&mut World, &mut App) + Send + Sync>,
@@ -143,20 +147,21 @@ pub struct SubApp {
 impl SubApp {
     /// Creates a new [`SubApp`].
     ///
-    /// The provided function `extract` is normally called by the [`update`](App::update) method.
+    /// The provided function `extract` is normally called by the [`run_schedule`](World::run_schedule) method.
     /// After extract is called, the [`Schedule`] of the sub app is run. The [`World`]
     /// parameter represents the main app world, while the [`App`] parameter is just a mutable
     /// reference to the `SubApp` itself.
     pub fn new(app: App, extract: impl Fn(&mut World, &mut App) + Send + Sync + 'static) -> Self {
         Self {
             app,
+            main_schedule_label: Box::new(Main),
             extract: Box::new(extract),
         }
     }
 
     /// Runs the [`SubApp`]'s default schedule.
     pub fn run(&mut self) {
-        self.app.world.run_schedule(&*self.app.main_schedule_label);
+        self.app.world.run_schedule(&*self.main_schedule_label);
         self.app.world.clear_trackers();
     }
 
@@ -219,38 +224,19 @@ impl App {
             sub_apps: HashMap::default(),
             plugin_registry: Vec::default(),
             plugin_name_added: Default::default(),
-            main_schedule_label: Box::new(Main),
             building_plugin_depth: 0,
         }
     }
 
-    /// Advances the execution of the [`Schedule`] by one cycle.
-    ///
-    /// This method also updates sub apps.
+    /// Update sub apps.
     /// See [`insert_sub_app`](Self::insert_sub_app) for more details.
-    ///
-    /// The schedule run by this method is determined by the [`main_schedule_label`](App) field.
-    /// By default this is [`Main`].
-    ///
-    /// # Panics
-    ///
-    /// The active schedule of the app must be set before this method is called.
-    pub fn update(&mut self) {
-        #[cfg(feature = "trace")]
-        let _bevy_update_span = info_span!("update").entered();
-        {
-            #[cfg(feature = "trace")]
-            let _bevy_main_update_span = info_span!("main app").entered();
-            self.world.run_schedule(&*self.main_schedule_label);
-        }
+    pub fn update_sub_apps(&mut self) {
         for (_label, sub_app) in self.sub_apps.iter_mut() {
             #[cfg(feature = "trace")]
             let _sub_app_span = info_span!("sub app", name = ?_label).entered();
             sub_app.extract(&mut self.world);
             sub_app.run();
         }
-
-        self.world.clear_trackers();
     }
 
     /// Starts the application by calling the app's [runner function](Self::set_runner).
@@ -293,7 +279,7 @@ impl App {
     }
 
     /// Check that [`Plugin::ready`] of all plugins returns true. This is usually called by the
-    /// event loop, but can be useful for situations where you want to use [`App::update`]
+    /// event loop, but can be useful for situations where you want to no use [`App::run`]
     pub fn ready(&self) -> bool {
         for plugin in &self.plugin_registry {
             if !plugin.ready(self) {
@@ -304,8 +290,8 @@ impl App {
     }
 
     /// Run [`Plugin::finish`] for each plugin. This is usually called by the event loop once all
-    /// plugins are [`App::ready`], but can be useful for situations where you want to use
-    /// [`App::update`].
+    /// plugins are [`App::ready`], but can be useful for situations where you want to no use
+    /// [`App::run`].
     pub fn finish(&mut self) {
         // temporarily remove the plugin registry to run each plugin's setup function on app.
         let plugin_registry = std::mem::take(&mut self.plugin_registry);
@@ -316,7 +302,7 @@ impl App {
     }
 
     /// Run [`Plugin::cleanup`] for each plugin. This is usually called by the event loop after
-    /// [`App::finish`], but can be useful for situations where you want to use [`App::update`].
+    /// [`App::finish`], but can be useful for situations where you want to no use [`App::run`].
     pub fn cleanup(&mut self) {
         // temporarily remove the plugin registry to run each plugin's setup function on app.
         let plugin_registry = std::mem::take(&mut self.plugin_registry);
@@ -636,6 +622,11 @@ impl App {
     /// The runner function is usually not set manually, but by Bevy integrated plugins
     /// (e.g. `WinitPlugin`).
     ///
+    /// # Note
+    ///
+    /// Inside the runner function, `World::clear_trackers()` must be called periodically.
+    /// If that isn't called on a world, it may lead to memory leaks in `RemovedComponents`.
+    ///
     /// # Examples
     ///
     /// ```
@@ -644,7 +635,7 @@ impl App {
     /// fn my_runner(mut app: App) {
     ///     loop {
     ///         println!("In main loop");
-    ///         app.update();
+    ///         app.world.run_schedule(Main);
     ///     }
     /// }
     ///
@@ -970,7 +961,12 @@ fn run_once(mut app: App) {
     app.finish();
     app.cleanup();
 
-    app.update();
+    {
+        #[cfg(feature = "trace")]
+        let _main_schedule_span = info_span!("main schedule", name = ?Main).entered();
+        app.world.run_schedule(Main);
+    }
+    app.update_sub_apps();
 }
 
 /// An event that indicates the [`App`] should exit. This will fully exit the app process at the

crates/bevy_app/src/main_schedule.rs

@@ -5,7 +5,7 @@ use bevy_ecs::{
     world::{Mut, World},
 };
 
-/// The schedule that contains the app logic that is evaluated each tick of [`App::update()`].
+/// The schedule that contains the app logic that is evaluated each tick of event loop.
 ///
 /// By default, it will run the following schedules in the given order:
 ///

crates/bevy_app/src/schedule_runner.rs

@@ -1,10 +1,17 @@
 use crate::{
     app::{App, AppExit},
     plugin::Plugin,
+    Main,
+};
+use bevy_ecs::{
+    event::{Events, ManualEventReader},
+    schedule::BoxedScheduleLabel,
 };
-use bevy_ecs::event::{Events, ManualEventReader};
 use bevy_utils::{Duration, Instant};
 
+#[cfg(feature = "trace")]
+use bevy_utils::tracing::info_span;
+
 #[cfg(target_arch = "wasm32")]
 use std::{cell::RefCell, rc::Rc};
 #[cfg(target_arch = "wasm32")]
@@ -43,17 +50,21 @@ impl Default for RunMode {
 /// typically, the `winit` event loop
 /// (see [`WinitPlugin`](https://docs.rs/bevy/latest/bevy/winit/struct.WinitPlugin.html))
 /// executes the schedule making [`ScheduleRunnerPlugin`] unnecessary.
-#[derive(Default)]
 pub struct ScheduleRunnerPlugin {
     /// Determines whether the [`Schedule`](bevy_ecs::schedule::Schedule) is run once or repeatedly.
     pub run_mode: RunMode,
+    /// The schedule to run by default.
+    ///
+    /// This is initially set to [`Main`].
+    pub main_schedule_label: BoxedScheduleLabel,
 }
 
 impl ScheduleRunnerPlugin {
     /// See [`RunMode::Once`].
     pub fn run_once() -> Self {
         ScheduleRunnerPlugin {
             run_mode: RunMode::Once,
+            main_schedule_label: Box::new(Main),
         }
     }
 
@@ -63,18 +74,38 @@ impl ScheduleRunnerPlugin {
             run_mode: RunMode::Loop {
                 wait: Some(wait_duration),
             },
+            main_schedule_label: Box::new(Main),
+        }
+    }
+}
+
+impl Default for ScheduleRunnerPlugin {
+    fn default() -> Self {
+        ScheduleRunnerPlugin {
+            run_mode: RunMode::Loop { wait: None },
+            main_schedule_label: Box::new(Main),
         }
     }
 }
 
 impl Plugin for ScheduleRunnerPlugin {
     fn build(&self, app: &mut App) {
         let run_mode = self.run_mode;
+        let main_schedule_label = self.main_schedule_label.clone();
         app.set_runner(move |mut app: App| {
+            // Prevent panic when schedules do not exist
+            app.init_schedule(main_schedule_label.clone());
+
             let mut app_exit_event_reader = ManualEventReader::<AppExit>::default();
             match run_mode {
                 RunMode::Once => {
-                    app.update();
+                    {
+                        #[cfg(feature = "trace")]
+                        let _main_schedule_span =
+                            info_span!("main schedule", name = ?main_schedule_label).entered();
+                        app.world.run_schedule(main_schedule_label);
+                    }
+                    app.update_sub_apps();
                 }
                 RunMode::Loop { wait } => {
                     let mut tick = move |app: &mut App,
@@ -91,7 +122,14 @@ impl Plugin for ScheduleRunnerPlugin {
                             }
                         }
 
-                        app.update();
+                        {
+                            #[cfg(feature = "trace")]
+                            let _main_schedule_span =
+                                info_span!("main schedule", name = ?main_schedule_label).entered();
+                            app.world.run_schedule(&main_schedule_label);
+                        }
+                        app.update_sub_apps();
+                        app.world.clear_trackers();
 
                         if let Some(app_exit_events) =
                             app.world.get_resource_mut::<Events<AppExit>>()

crates/bevy_asset/src/asset_server.rs

@@ -645,7 +645,7 @@ pub fn free_unused_assets_system(asset_server: Res<AssetServer>) {
 mod test {
     use super::*;
     use crate::{loader::LoadedAsset, update_asset_storage_system};
-    use bevy_app::{App, Update};
+    use bevy_app::{App, Main, Update};
     use bevy_ecs::prelude::*;
     use bevy_reflect::{TypePath, TypeUuid};
     use bevy_utils::BoxedFuture;
@@ -896,19 +896,19 @@ mod test {
         // asset is loading
         assert_eq!(LoadState::Loading, get_load_state(&handle, &app.world));
 
-        app.update();
+        app.world.run_schedule(Main);
         // asset should exist and be loaded at this point
         assert_eq!(LoadState::Loaded, get_load_state(&handle, &app.world));
         assert!(get_asset(&handle, &app.world).is_some());
 
         // after dropping the handle, next call to `tick` will prepare the assets for removal.
         drop(handle);
-        app.update();
+        app.world.run_schedule(Main);
         assert_eq!(LoadState::Loaded, get_load_state(&weak_handle, &app.world));
         assert!(get_asset(&weak_handle, &app.world).is_some());
 
         // second call to tick will actually remove the asset.
-        app.update();
+        app.world.run_schedule(Main);
         assert_eq!(
             LoadState::Unloaded,
             get_load_state(&weak_handle, &app.world)
@@ -918,7 +918,7 @@ mod test {
         // finally, reload the asset
         let handle = load_asset(path.clone(), &app.world).typed();
         assert_eq!(LoadState::Loading, get_load_state(&handle, &app.world));
-        app.update();
+        app.world.run_schedule(Main);
         assert_eq!(LoadState::Loaded, get_load_state(&handle, &app.world));
         assert!(get_asset(&handle, &app.world).is_some());
     }

crates/bevy_asset/src/debug_asset_server.rs

@@ -2,7 +2,7 @@
 //!
 //! Internal assets (e.g. shaders) are bundled directly into an application and can't be hot
 //! reloaded using the conventional API.
-use bevy_app::{App, Plugin, Update};
+use bevy_app::{App, Main, Plugin, Update};
 use bevy_ecs::{prelude::*, system::SystemState};
 use bevy_tasks::{IoTaskPool, TaskPoolBuilder};
 use bevy_utils::{Duration, HashMap};
@@ -81,7 +81,7 @@ impl Plugin for DebugAssetServerPlugin {
 }
 
 fn run_debug_asset_app(mut debug_asset_app: NonSendMut<DebugAssetApp>) {
-    debug_asset_app.0.update();
+    debug_asset_app.0.world.run_schedule(Main);
 }
 
 pub(crate) fn sync_debug_assets<T: Asset + Clone>(

crates/bevy_core/src/lib.rs

@@ -203,7 +203,7 @@ mod tests {
             TypeRegistrationPlugin::default(),
             FrameCountPlugin::default(),
         ));
-        app.update();
+        app.world.run_schedule(Main);
 
         let frame_count = app.world.resource::<FrameCount>();
         assert_eq!(1, frame_count.0);

crates/bevy_render/src/lib.rs

@@ -266,7 +266,6 @@ impl Plugin for RenderPlugin {
             app.init_resource::<ScratchMainWorld>();
 
             let mut render_app = App::empty();
-            render_app.main_schedule_label = Box::new(Render);
 
             let mut extract_schedule = Schedule::new();
             extract_schedule.set_apply_final_deferred(false);
@@ -296,14 +295,14 @@ impl Plugin for RenderPlugin {
             app.insert_resource(receiver);
             render_app.insert_resource(sender);
 
-            app.insert_sub_app(RenderApp, SubApp::new(render_app, move |main_world, render_app| {
+            let mut sub_app = SubApp::new(render_app, move |main_world, render_app| {
                 #[cfg(feature = "trace")]
-                let _render_span = bevy_utils::tracing::info_span!("extract main app to render subapp").entered();
+                let _render_span =
+                    bevy_utils::tracing::info_span!("extract main app to render subapp").entered();
                 {
                     #[cfg(feature = "trace")]
                     let _stage_span =
-                        bevy_utils::tracing::info_span!("reserve_and_flush")
-                            .entered();
+                        bevy_utils::tracing::info_span!("reserve_and_flush").entered();
 
                     // reserve all existing main world entities for use in render_app
                     // they can only be spawned using `get_or_spawn()`
@@ -326,7 +325,9 @@ impl Plugin for RenderPlugin {
 
                 // run extract schedule
                 extract(main_world, render_app);
-            }));
+            });
+            sub_app.main_schedule_label = Box::new(Render);
+            app.insert_sub_app(RenderApp, sub_app);
         }
 
         app.add_plugins((