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executor_parallel.rs
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executor_parallel.rs
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use crate::{
archetype::ArchetypeComponentId,
query::Access,
schedule::{ParallelSystemContainer, ParallelSystemExecutor},
world::World,
};
use async_channel::{Receiver, Sender};
use bevy_tasks::{ComputeTaskPool, Scope, TaskPool};
#[cfg(feature = "trace")]
use bevy_utils::tracing::Instrument;
use fixedbitset::FixedBitSet;
#[cfg(test)]
use SchedulingEvent::*;
struct SystemSchedulingMetadata {
/// Used to signal the system's task to start the system.
start_sender: Sender<()>,
/// Receives the signal to start the system.
start_receiver: Receiver<()>,
/// Indices of systems that depend on this one, used to decrement their
/// dependency counters when this system finishes.
dependants: Vec<usize>,
/// Total amount of dependencies this system has.
dependencies_total: usize,
/// Amount of unsatisfied dependencies, when it reaches 0 the system is queued to be started.
dependencies_now: usize,
/// Archetype-component access information.
archetype_component_access: Access<ArchetypeComponentId>,
/// Whether or not this system is send-able
is_send: bool,
}
pub struct ParallelExecutor {
/// Cached metadata of every system.
system_metadata: Vec<SystemSchedulingMetadata>,
/// Used by systems to notify the executor that they have finished.
finish_sender: Sender<usize>,
/// Receives finish events from systems.
finish_receiver: Receiver<usize>,
/// Systems that should be started at next opportunity.
queued: FixedBitSet,
/// Systems that are currently running.
running: FixedBitSet,
/// Whether a non-send system is currently running.
non_send_running: bool,
/// Systems that should run this iteration.
should_run: FixedBitSet,
/// Compound archetype-component access information of currently running systems.
active_archetype_component_access: Access<ArchetypeComponentId>,
/// Scratch space to avoid reallocating a vector when updating dependency counters.
dependants_scratch: Vec<usize>,
#[cfg(test)]
events_sender: Option<Sender<SchedulingEvent>>,
}
impl Default for ParallelExecutor {
fn default() -> Self {
let (finish_sender, finish_receiver) = async_channel::unbounded();
Self {
system_metadata: Default::default(),
finish_sender,
finish_receiver,
queued: Default::default(),
running: Default::default(),
non_send_running: false,
should_run: Default::default(),
active_archetype_component_access: Default::default(),
dependants_scratch: Default::default(),
#[cfg(test)]
events_sender: None,
}
}
}
impl ParallelSystemExecutor for ParallelExecutor {
fn rebuild_cached_data(&mut self, systems: &[ParallelSystemContainer]) {
self.system_metadata.clear();
self.queued.grow(systems.len());
self.running.grow(systems.len());
self.should_run.grow(systems.len());
// Construct scheduling data for systems.
for container in systems.iter() {
let dependencies_total = container.dependencies().len();
let system = container.system();
let (start_sender, start_receiver) = async_channel::bounded(1);
self.system_metadata.push(SystemSchedulingMetadata {
start_sender,
start_receiver,
dependants: vec![],
dependencies_total,
dependencies_now: 0,
is_send: system.is_send(),
archetype_component_access: Default::default(),
});
}
// Populate the dependants lists in the scheduling metadata.
for (dependant, container) in systems.iter().enumerate() {
for dependency in container.dependencies() {
self.system_metadata[*dependency].dependants.push(dependant);
}
}
}
fn run_systems(&mut self, systems: &mut [ParallelSystemContainer], world: &mut World) {
#[cfg(test)]
if self.events_sender.is_none() {
let (sender, receiver) = async_channel::unbounded::<SchedulingEvent>();
world.insert_resource(receiver);
self.events_sender = Some(sender);
}
{
#[cfg(feature = "trace")]
let _span = bevy_utils::tracing::info_span!("update_archetypes").entered();
for (index, container) in systems.iter_mut().enumerate() {
let meta = &mut self.system_metadata[index];
let system = container.system_mut();
system.update_archetype_component_access(world);
meta.archetype_component_access
.extend(system.archetype_component_access());
}
}
let compute_pool = world
.get_resource_or_insert_with(|| ComputeTaskPool(TaskPool::default()))
.clone();
compute_pool.scope(|scope| {
self.prepare_systems(scope, systems, world);
let parallel_executor = async {
// All systems have been ran if there are no queued or running systems.
while 0 != self.queued.count_ones(..) + self.running.count_ones(..) {
self.process_queued_systems().await;
// Avoid deadlocking if no systems were actually started.
if self.running.count_ones(..) != 0 {
// Wait until at least one system has finished.
let index = self
.finish_receiver
.recv()
.await
.unwrap_or_else(|error| unreachable!("{}", error));
self.process_finished_system(index);
// Gather other systems than may have finished.
while let Ok(index) = self.finish_receiver.try_recv() {
self.process_finished_system(index);
}
// At least one system has finished, so active access is outdated.
self.rebuild_active_access();
}
self.update_counters_and_queue_systems();
}
};
#[cfg(feature = "trace")]
let span = bevy_utils::tracing::info_span!("parallel executor");
#[cfg(feature = "trace")]
let parallel_executor = parallel_executor.instrument(span);
scope.spawn(parallel_executor);
});
}
}
impl ParallelExecutor {
/// Populates `should_run` bitset, spawns tasks for systems that should run this iteration,
/// queues systems with no dependencies to run (or skip) at next opportunity.
fn prepare_systems<'scope>(
&mut self,
scope: &mut Scope<'scope, ()>,
systems: &'scope mut [ParallelSystemContainer],
world: &'scope World,
) {
#[cfg(feature = "trace")]
let _span = bevy_utils::tracing::info_span!("prepare_systems").entered();
self.should_run.clear();
for (index, (system_data, system)) in
self.system_metadata.iter_mut().zip(systems).enumerate()
{
// Spawn the system task.
if system.should_run() {
self.should_run.set(index, true);
let start_receiver = system_data.start_receiver.clone();
let finish_sender = self.finish_sender.clone();
let system = system.system_mut();
#[cfg(feature = "trace")] // NB: outside the task to get the TLS current span
let system_span = bevy_utils::tracing::info_span!("system", name = &*system.name());
#[cfg(feature = "trace")]
let overhead_span =
bevy_utils::tracing::info_span!("system overhead", name = &*system.name());
let task = async move {
start_receiver
.recv()
.await
.unwrap_or_else(|error| unreachable!("{}", error));
#[cfg(feature = "trace")]
let system_guard = system_span.enter();
unsafe { system.run_unsafe((), world) };
#[cfg(feature = "trace")]
drop(system_guard);
finish_sender
.send(index)
.await
.unwrap_or_else(|error| unreachable!("{}", error));
};
#[cfg(feature = "trace")]
let task = task.instrument(overhead_span);
if system_data.is_send {
scope.spawn(task);
} else {
scope.spawn_local(task);
}
}
// Queue the system if it has no dependencies, otherwise reset its dependency counter.
if system_data.dependencies_total == 0 {
self.queued.insert(index);
} else {
system_data.dependencies_now = system_data.dependencies_total;
}
}
}
/// Determines if the system with given index has no conflicts with already running systems.
fn can_start_now(&self, index: usize) -> bool {
let system_data = &self.system_metadata[index];
// Non-send systems are considered conflicting with each other.
(!self.non_send_running || system_data.is_send)
&& system_data
.archetype_component_access
.is_compatible(&self.active_archetype_component_access)
}
/// Starts all non-conflicting queued systems, moves them from `queued` to `running`,
/// adds their access information to active access information;
/// processes queued systems that shouldn't run this iteration as completed immediately.
async fn process_queued_systems(&mut self) {
#[cfg(test)]
let mut started_systems = 0;
for index in self.queued.ones() {
// If the system shouldn't actually run this iteration, process it as completed
// immediately; otherwise, check for conflicts and signal its task to start.
let system_metadata = &self.system_metadata[index];
if !self.should_run[index] {
self.dependants_scratch.extend(&system_metadata.dependants);
} else if self.can_start_now(index) {
#[cfg(test)]
{
started_systems += 1;
}
system_metadata
.start_sender
.send(())
.await
.unwrap_or_else(|error| unreachable!("{}", error));
self.running.set(index, true);
if !system_metadata.is_send {
self.non_send_running = true;
}
// Add this system's access information to the active access information.
self.active_archetype_component_access
.extend(&system_metadata.archetype_component_access);
}
}
#[cfg(test)]
if started_systems != 0 {
self.emit_event(StartedSystems(started_systems));
}
// Remove now running systems from the queue.
self.queued.difference_with(&self.running);
// Remove immediately processed systems from the queue.
self.queued.intersect_with(&self.should_run);
}
/// Unmarks the system give index as running, caches indices of its dependants
/// in the `dependants_scratch`.
fn process_finished_system(&mut self, index: usize) {
let system_data = &self.system_metadata[index];
if !system_data.is_send {
self.non_send_running = false;
}
self.running.set(index, false);
self.dependants_scratch.extend(&system_data.dependants);
}
/// Discards active access information and builds it again using currently
/// running systems' access information.
fn rebuild_active_access(&mut self) {
self.active_archetype_component_access.clear();
for index in self.running.ones() {
self.active_archetype_component_access
.extend(&self.system_metadata[index].archetype_component_access);
}
}
/// Drains `dependants_scratch`, decrementing dependency counters and enqueueing any
/// systems that become able to run.
fn update_counters_and_queue_systems(&mut self) {
for index in self.dependants_scratch.drain(..) {
let dependant_data = &mut self.system_metadata[index];
dependant_data.dependencies_now -= 1;
if dependant_data.dependencies_now == 0 {
self.queued.insert(index);
}
}
}
#[cfg(test)]
fn emit_event(&self, event: SchedulingEvent) {
let _ = self.events_sender.as_ref().unwrap().try_send(event);
}
}
#[cfg(test)]
#[derive(Debug, PartialEq, Eq)]
enum SchedulingEvent {
StartedSystems(usize),
}
#[cfg(test)]
mod tests {
use super::SchedulingEvent::{self, *};
use crate::{
schedule::{SingleThreadedExecutor, Stage, SystemStage},
system::{NonSend, Query, Res, ResMut},
world::World,
};
use async_channel::Receiver;
use crate as bevy_ecs;
use crate::component::Component;
#[derive(Component)]
struct W<T>(T);
fn receive_events(world: &World) -> Vec<SchedulingEvent> {
let mut events = Vec::new();
while let Ok(event) = world.resource::<Receiver<SchedulingEvent>>().try_recv() {
events.push(event);
}
events
}
#[test]
fn trivial() {
let mut world = World::new();
fn wants_for_nothing() {}
let mut stage = SystemStage::parallel()
.with_system(wants_for_nothing)
.with_system(wants_for_nothing)
.with_system(wants_for_nothing);
stage.run(&mut world);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(3), StartedSystems(3),]
);
}
#[test]
fn resources() {
let mut world = World::new();
world.insert_resource(0usize);
fn wants_mut(_: ResMut<usize>) {}
fn wants_ref(_: Res<usize>) {}
let mut stage = SystemStage::parallel()
.with_system(wants_mut)
.with_system(wants_mut);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(1), StartedSystems(1),]
);
let mut stage = SystemStage::parallel()
.with_system(wants_mut)
.with_system(wants_ref);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(1), StartedSystems(1),]
);
let mut stage = SystemStage::parallel()
.with_system(wants_ref)
.with_system(wants_ref);
stage.run(&mut world);
assert_eq!(receive_events(&world), vec![StartedSystems(2),]);
}
#[test]
fn queries() {
let mut world = World::new();
world.spawn().insert(W(0usize));
fn wants_mut(_: Query<&mut W<usize>>) {}
fn wants_ref(_: Query<&W<usize>>) {}
let mut stage = SystemStage::parallel()
.with_system(wants_mut)
.with_system(wants_mut);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(1), StartedSystems(1),]
);
let mut stage = SystemStage::parallel()
.with_system(wants_mut)
.with_system(wants_ref);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(1), StartedSystems(1),]
);
let mut stage = SystemStage::parallel()
.with_system(wants_ref)
.with_system(wants_ref);
stage.run(&mut world);
assert_eq!(receive_events(&world), vec![StartedSystems(2),]);
let mut world = World::new();
world.spawn().insert_bundle((W(0usize), W(0u32), W(0f32)));
fn wants_mut_usize(_: Query<(&mut W<usize>, &W<f32>)>) {}
fn wants_mut_u32(_: Query<(&mut W<u32>, &W<f32>)>) {}
let mut stage = SystemStage::parallel()
.with_system(wants_mut_usize)
.with_system(wants_mut_u32);
stage.run(&mut world);
assert_eq!(receive_events(&world), vec![StartedSystems(2),]);
}
#[test]
fn world() {
let mut world = World::new();
world.spawn().insert(W(0usize));
fn wants_world(_: &World) {}
fn wants_mut(_: Query<&mut W<usize>>) {}
let mut stage = SystemStage::parallel()
.with_system(wants_mut)
.with_system(wants_mut);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(1), StartedSystems(1),]
);
let mut stage = SystemStage::parallel()
.with_system(wants_mut)
.with_system(wants_world);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![StartedSystems(1), StartedSystems(1),]
);
let mut stage = SystemStage::parallel()
.with_system(wants_world)
.with_system(wants_world);
stage.run(&mut world);
assert_eq!(receive_events(&world), vec![StartedSystems(2),]);
}
#[test]
fn non_send_resource() {
use std::thread;
let mut world = World::new();
world.insert_non_send_resource(thread::current().id());
fn non_send(thread_id: NonSend<thread::ThreadId>) {
assert_eq!(thread::current().id(), *thread_id);
}
fn empty() {}
let mut stage = SystemStage::parallel()
.with_system(non_send)
.with_system(non_send)
.with_system(empty)
.with_system(empty)
.with_system(non_send)
.with_system(non_send);
stage.run(&mut world);
assert_eq!(
receive_events(&world),
vec![
StartedSystems(3),
StartedSystems(1),
StartedSystems(1),
StartedSystems(1),
]
);
stage.set_executor(Box::new(SingleThreadedExecutor::default()));
stage.run(&mut world);
}
}