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//! Tools for controlling system execution.
//!
//! When using Bevy ECS, systems are usually not run directly, but are inserted into a
//! [`Stage`], which then lives within a [`Schedule`].
mod executor;
mod executor_parallel;
pub mod graph_utils;
mod label;
mod run_criteria;
mod stage;
mod state;
mod system_container;
mod system_descriptor;
mod system_set;
pub use executor::*;
pub use executor_parallel::*;
pub use graph_utils::GraphNode;
pub use label::*;
pub use run_criteria::*;
pub use stage::*;
pub use state::*;
pub use system_container::*;
pub use system_descriptor::*;
pub use system_set::*;
use std::fmt::Debug;
use crate::{system::System, world::World};
use bevy_utils::HashMap;
/// A container of [`Stage`]s set to be run in a linear order.
///
/// Since `Schedule` implements the [`Stage`] trait, it can be inserted into another schedule.
/// In this way, the properties of the child schedule can be set differently from the parent.
/// For example, it can be set to run only once during app execution, while the parent schedule
/// runs indefinitely.
#[derive(Default)]
pub struct Schedule {
stages: HashMap<BoxedStageLabel, Box<dyn Stage>>,
stage_order: Vec<BoxedStageLabel>,
run_criteria: BoxedRunCriteria,
}
impl Schedule {
/// Similar to [`add_stage`](Self::add_stage), but it also returns itself.
pub fn with_stage<S: Stage>(mut self, label: impl StageLabel, stage: S) -> Self {
self.add_stage(label, stage);
self
}
/// Similar to [`add_stage_after`](Self::add_stage_after), but it also returns itself.
pub fn with_stage_after<S: Stage>(
mut self,
target: impl StageLabel,
label: impl StageLabel,
stage: S,
) -> Self {
self.add_stage_after(target, label, stage);
self
}
/// Similar to [`add_stage_before`](Self::add_stage_before), but it also returns itself.
pub fn with_stage_before<S: Stage>(
mut self,
target: impl StageLabel,
label: impl StageLabel,
stage: S,
) -> Self {
self.add_stage_before(target, label, stage);
self
}
pub fn with_run_criteria<S: System<In = (), Out = ShouldRun>>(mut self, system: S) -> Self {
self.set_run_criteria(system);
self
}
/// Similar to [`add_system_to_stage`](Self::add_system_to_stage), but it also returns itself.
pub fn with_system_in_stage<Params>(
mut self,
stage_label: impl StageLabel,
system: impl IntoSystemDescriptor<Params>,
) -> Self {
self.add_system_to_stage(stage_label, system);
self
}
pub fn set_run_criteria<S: System<In = (), Out = ShouldRun>>(
&mut self,
system: S,
) -> &mut Self {
self.run_criteria.set(Box::new(system));
self
}
/// Adds the given `stage` at the last position of the schedule.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # let mut schedule = Schedule::default();
/// schedule.add_stage("my_stage", SystemStage::parallel());
/// ```
pub fn add_stage<S: Stage>(&mut self, label: impl StageLabel, stage: S) -> &mut Self {
let label: Box<dyn StageLabel> = Box::new(label);
self.stage_order.push(label.clone());
let prev = self.stages.insert(label.clone(), Box::new(stage));
if prev.is_some() {
panic!("Stage already exists: {:?}.", label);
}
self
}
/// Adds the given `stage` immediately after the `target` stage.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("target_stage", SystemStage::parallel());
/// schedule.add_stage_after("target_stage", "my_stage", SystemStage::parallel());
/// ```
pub fn add_stage_after<S: Stage>(
&mut self,
target: impl StageLabel,
label: impl StageLabel,
stage: S,
) -> &mut Self {
let label: Box<dyn StageLabel> = Box::new(label);
let target = &target as &dyn StageLabel;
let target_index = self
.stage_order
.iter()
.enumerate()
.find(|(_i, stage_label)| &***stage_label == target)
.map(|(i, _)| i)
.unwrap_or_else(|| panic!("Target stage does not exist: {:?}.", target));
self.stage_order.insert(target_index + 1, label.clone());
let prev = self.stages.insert(label.clone(), Box::new(stage));
if prev.is_some() {
panic!("Stage already exists: {:?}.", label);
}
self
}
/// Adds the given `stage` immediately before the `target` stage.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("target_stage", SystemStage::parallel());
/// #
/// schedule.add_stage_before("target_stage", "my_stage", SystemStage::parallel());
/// ```
pub fn add_stage_before<S: Stage>(
&mut self,
target: impl StageLabel,
label: impl StageLabel,
stage: S,
) -> &mut Self {
let label: Box<dyn StageLabel> = Box::new(label);
let target = &target as &dyn StageLabel;
let target_index = self
.stage_order
.iter()
.enumerate()
.find(|(_i, stage_label)| &***stage_label == target)
.map(|(i, _)| i)
.unwrap_or_else(|| panic!("Target stage does not exist: {:?}.", target));
self.stage_order.insert(target_index, label.clone());
let prev = self.stages.insert(label.clone(), Box::new(stage));
if prev.is_some() {
panic!("Stage already exists: {:?}.", label);
}
self
}
/// Adds the given `system` to the stage identified by `stage_label`.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # fn my_system() {}
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("my_stage", SystemStage::parallel());
/// #
/// schedule.add_system_to_stage("my_stage", my_system);
/// ```
pub fn add_system_to_stage<Params>(
&mut self,
stage_label: impl StageLabel,
system: impl IntoSystemDescriptor<Params>,
) -> &mut Self {
// Use a function instead of a closure to ensure that it is codegend inside bevy_ecs instead
// of the game. Closures inherit generic parameters from their enclosing function.
#[cold]
fn stage_not_found(stage_label: &dyn Debug) -> ! {
panic!(
"Stage '{:?}' does not exist or is not a SystemStage",
stage_label
)
}
let stage = self
.get_stage_mut::<SystemStage>(&stage_label)
.unwrap_or_else(move || stage_not_found(&stage_label));
stage.add_system(system);
self
}
/// Adds the given `system_set` to the stage identified by `stage_label`.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # fn my_system() {}
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("my_stage", SystemStage::parallel());
/// #
/// schedule.add_system_set_to_stage(
/// "my_stage",
/// SystemSet::new()
/// .with_system(system_a)
/// .with_system(system_b)
/// .with_system(system_c)
/// );
/// #
/// # fn system_a() {}
/// # fn system_b() {}
/// # fn system_c() {}
/// ```
pub fn add_system_set_to_stage(
&mut self,
stage_label: impl StageLabel,
system_set: SystemSet,
) -> &mut Self {
self.stage(stage_label, |stage: &mut SystemStage| {
stage.add_system_set(system_set)
})
}
/// Fetches the [`Stage`] of type `T` marked with `label`, then executes the provided
/// `func` passing the fetched stage to it as an argument.
///
/// The `func` argument should be a function or a closure that accepts a mutable reference
/// to a struct implementing `Stage` and returns the same type. That means that it should
/// also assume that the stage has already been fetched successfully.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("my_stage", SystemStage::parallel());
/// #
/// schedule.stage("my_stage", |stage: &mut SystemStage| {
/// stage.add_system(my_system)
/// });
/// #
/// # fn my_system() {}
/// ```
///
/// # Panics
///
/// Panics if `label` refers to a non-existing stage, or if it's not of type `T`.
pub fn stage<T: Stage, F: FnOnce(&mut T) -> &mut T>(
&mut self,
label: impl StageLabel,
func: F,
) -> &mut Self {
let stage = self.get_stage_mut::<T>(&label).unwrap_or_else(move || {
panic!("stage '{:?}' does not exist or is the wrong type", label)
});
func(stage);
self
}
/// Returns a shared reference to the stage identified by `label`, if it exists.
///
/// If the requested stage does not exist, `None` is returned instead.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # fn my_system() {}
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("my_stage", SystemStage::parallel());
/// #
/// let stage = schedule.get_stage::<SystemStage>(&"my_stage").unwrap();
/// ```
pub fn get_stage<T: Stage>(&self, label: &dyn StageLabel) -> Option<&T> {
self.stages
.get(label)
.and_then(|stage| stage.downcast_ref::<T>())
}
/// Returns a unique, mutable reference to the stage identified by `label`, if it exists.
///
/// If the requested stage does not exist, `None` is returned instead.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # fn my_system() {}
/// # let mut schedule = Schedule::default();
/// # schedule.add_stage("my_stage", SystemStage::parallel());
/// #
/// let stage = schedule.get_stage_mut::<SystemStage>(&"my_stage").unwrap();
/// ```
pub fn get_stage_mut<T: Stage>(&mut self, label: &dyn StageLabel) -> Option<&mut T> {
self.stages
.get_mut(label)
.and_then(|stage| stage.downcast_mut::<T>())
}
/// Executes each [`Stage`] contained in the schedule, one at a time.
pub fn run_once(&mut self, world: &mut World) {
for label in self.stage_order.iter() {
#[cfg(feature = "trace")]
let stage_span = bevy_utils::tracing::info_span!("stage", name = ?label);
#[cfg(feature = "trace")]
let _stage_guard = stage_span.enter();
let stage = self.stages.get_mut(label).unwrap();
stage.run(world);
}
}
/// Iterates over all of schedule's stages and their labels, in execution order.
pub fn iter_stages(&self) -> impl Iterator<Item = (&dyn StageLabel, &dyn Stage)> {
self.stage_order
.iter()
.map(move |label| (&**label, &*self.stages[label]))
}
}
impl Stage for Schedule {
fn run(&mut self, world: &mut World) {
loop {
match self.run_criteria.should_run(world) {
ShouldRun::No => return,
ShouldRun::Yes => {
self.run_once(world);
return;
}
ShouldRun::YesAndCheckAgain => {
self.run_once(world);
}
ShouldRun::NoAndCheckAgain => {
panic!("`NoAndCheckAgain` would loop infinitely in this situation.")
}
}
}
}
}