Stop using ArchetypeComponentId in the executor (#16885)

# Objective

Stop using `ArchetypeComponentId` in the executor. These IDs will grow
even more quickly with relations, and the size may start to degrade
performance.

## Solution

Have systems expose their `FilteredAccessSet<ComponentId>`, and have the
executor use that to determine which systems conflict. This can be
determined statically, so determine all conflicts during initialization
and only perform bit tests when running.

## Testing

I ran many_foxes and didn't see any performance changes. It's probably
worth testing this with a wider range of realistic schedules to see
whether the reduced concurrency has a cost in practice, but I don't know
what sort of test cases to use.

## Migration Guide

The schedule will now prevent systems from running in parallel if there
*could* be an archetype that they conflict on, even if there aren't
actually any. For example, these systems will now conflict even if no
entity has both `Player` and `Enemy` components:
```rust
fn player_system(query: Query<(&mut Transform, &Player)>) {}
fn enemy_system(query: Query<(&mut Transform, &Enemy)>) {}
```

To allow them to run in parallel, use `Without` filters, just as you
would to allow both queries in a single system:
```rust
// Either one of these changes alone would be enough
fn player_system(query: Query<(&mut Transform, &Player), Without<Enemy>>) {}
fn enemy_system(query: Query<(&mut Transform, &Enemy), Without<Player>>) {}
```

crates/bevy_ecs/src/query/access.rs

@@ -1289,6 +1289,14 @@ impl<T: SparseSetIndex> Clone for FilteredAccessSet<T> {
 }
 
 impl<T: SparseSetIndex> FilteredAccessSet<T> {
+    /// Creates an empty [`FilteredAccessSet`].
+    pub const fn new() -> Self {
+        Self {
+            combined_access: Access::new(),
+            filtered_accesses: Vec::new(),
+        }
+    }
+
     /// Returns a reference to the unfiltered access of the entire set.
     #[inline]
     pub fn combined_access(&self) -> &Access<T> {
@@ -1412,10 +1420,7 @@ impl<T: SparseSetIndex> FilteredAccessSet<T> {
 
 impl<T: SparseSetIndex> Default for FilteredAccessSet<T> {
     fn default() -> Self {
-        Self {
+        Self::new()
-            combined_access: Default::default(),
-            filtered_accesses: Vec::new(),
-        }
     }
 }
 

crates/bevy_ecs/src/schedule/executor/mod.rs

@@ -18,7 +18,7 @@ use crate::{
     component::{ComponentId, Tick},
     error::{BevyError, ErrorContext, Result},
     prelude::{IntoSystemSet, SystemSet},
-    query::Access,
+    query::{Access, FilteredAccessSet},
     schedule::{BoxedCondition, InternedSystemSet, NodeId, SystemTypeSet},
     system::{ScheduleSystem, System, SystemIn, SystemParamValidationError},
     world::{unsafe_world_cell::UnsafeWorldCell, DeferredWorld, World},
@@ -174,6 +174,10 @@ impl System for ApplyDeferred {
         const { &Access::new() }
     }
 
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        const { &FilteredAccessSet::new() }
+    }
+
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
         // This system accesses no archetype components.
         const { &Access::new() }

crates/bevy_ecs/src/schedule/executor/multi_threaded.rs

@@ -1,7 +1,7 @@
 use alloc::{boxed::Box, vec::Vec};
 use bevy_platform::sync::Arc;
 use bevy_tasks::{ComputeTaskPool, Scope, TaskPool, ThreadExecutor};
-use bevy_utils::{default, syncunsafecell::SyncUnsafeCell};
+use bevy_utils::syncunsafecell::SyncUnsafeCell;
 use concurrent_queue::ConcurrentQueue;
 use core::{any::Any, panic::AssertUnwindSafe};
 use fixedbitset::FixedBitSet;
@@ -13,10 +13,8 @@ use std::sync::{Mutex, MutexGuard};
 use tracing::{info_span, Span};
 
 use crate::{
-    archetype::ArchetypeComponentId,
     error::{default_error_handler, BevyError, ErrorContext, Result},
     prelude::Resource,
-    query::Access,
     schedule::{is_apply_deferred, BoxedCondition, ExecutorKind, SystemExecutor, SystemSchedule},
     system::ScheduleSystem,
     world::{unsafe_world_cell::UnsafeWorldCell, World},
@@ -62,8 +60,13 @@ impl<'env, 'sys> Environment<'env, 'sys> {
 /// Per-system data used by the [`MultiThreadedExecutor`].
 // Copied here because it can't be read from the system when it's running.
 struct SystemTaskMetadata {
-    /// The [`ArchetypeComponentId`] access of the system.
+    /// The set of systems whose `component_access_set()` conflicts with this one.
-    archetype_component_access: Access<ArchetypeComponentId>,
+    conflicting_systems: FixedBitSet,
+    /// The set of systems whose `component_access_set()` conflicts with this system's conditions.
+    /// Note that this is separate from `conflicting_systems` to handle the case where
+    /// a system is skipped by an earlier system set condition or system stepping,
+    /// and needs access to run its conditions but not for itself.
+    condition_conflicting_systems: FixedBitSet,
     /// Indices of the systems that directly depend on the system.
     dependents: Vec<usize>,
     /// Is `true` if the system does not access `!Send` data.
@@ -97,8 +100,8 @@ pub struct MultiThreadedExecutor {
 pub struct ExecutorState {
     /// Metadata for scheduling and running system tasks.
     system_task_metadata: Vec<SystemTaskMetadata>,
-    /// Union of the accesses of all currently running systems.
+    /// The set of systems whose `component_access_set()` conflicts with this system set's conditions.
-    active_access: Access<ArchetypeComponentId>,
+    set_condition_conflicting_systems: Vec<FixedBitSet>,
     /// Returns `true` if a system with non-`Send` access is running.
     local_thread_running: bool,
     /// Returns `true` if an exclusive system is running.
@@ -164,7 +167,8 @@ impl SystemExecutor for MultiThreadedExecutor {
         state.system_task_metadata = Vec::with_capacity(sys_count);
         for index in 0..sys_count {
             state.system_task_metadata.push(SystemTaskMetadata {
-                archetype_component_access: default(),
+                conflicting_systems: FixedBitSet::with_capacity(sys_count),
+                condition_conflicting_systems: FixedBitSet::with_capacity(sys_count),
                 dependents: schedule.system_dependents[index].clone(),
                 is_send: schedule.systems[index].is_send(),
                 is_exclusive: schedule.systems[index].is_exclusive(),
@@ -174,6 +178,60 @@ impl SystemExecutor for MultiThreadedExecutor {
             }
         }
 
+        {
+            #[cfg(feature = "trace")]
+            let _span = info_span!("calculate conflicting systems").entered();
+            for index1 in 0..sys_count {
+                let system1 = &schedule.systems[index1];
+                for index2 in 0..index1 {
+                    let system2 = &schedule.systems[index2];
+                    if !system2
+                        .component_access_set()
+                        .is_compatible(system1.component_access_set())
+                    {
+                        state.system_task_metadata[index1]
+                            .conflicting_systems
+                            .insert(index2);
+                        state.system_task_metadata[index2]
+                            .conflicting_systems
+                            .insert(index1);
+                    }
+                }
+
+                for index2 in 0..sys_count {
+                    let system2 = &schedule.systems[index2];
+                    if schedule.system_conditions[index1].iter().any(|condition| {
+                        !system2
+                            .component_access_set()
+                            .is_compatible(condition.component_access_set())
+                    }) {
+                        state.system_task_metadata[index1]
+                            .condition_conflicting_systems
+                            .insert(index2);
+                    }
+                }
+            }
+
+            state.set_condition_conflicting_systems.clear();
+            state.set_condition_conflicting_systems.reserve(set_count);
+            for set_idx in 0..set_count {
+                let mut conflicting_systems = FixedBitSet::with_capacity(sys_count);
+                for sys_index in 0..sys_count {
+                    let system = &schedule.systems[sys_index];
+                    if schedule.set_conditions[set_idx].iter().any(|condition| {
+                        !system
+                            .component_access_set()
+                            .is_compatible(condition.component_access_set())
+                    }) {
+                        conflicting_systems.insert(sys_index);
+                    }
+                }
+                state
+                    .set_condition_conflicting_systems
+                    .push(conflicting_systems);
+            }
+        }
+
         state.num_dependencies_remaining = Vec::with_capacity(sys_count);
     }
 
@@ -257,7 +315,6 @@ impl SystemExecutor for MultiThreadedExecutor {
 
         debug_assert!(state.ready_systems.is_clear());
         debug_assert!(state.running_systems.is_clear());
-        state.active_access.clear();
         state.evaluated_sets.clear();
         state.skipped_systems.clear();
         state.completed_systems.clear();
@@ -345,9 +402,9 @@ impl ExecutorState {
     fn new() -> Self {
         Self {
             system_task_metadata: Vec::new(),
+            set_condition_conflicting_systems: Vec::new(),
             num_running_systems: 0,
             num_dependencies_remaining: Vec::new(),
-            active_access: default(),
             local_thread_running: false,
             exclusive_running: false,
             evaluated_sets: FixedBitSet::new(),
@@ -368,8 +425,6 @@ impl ExecutorState {
             self.finish_system_and_handle_dependents(result);
         }
 
-        self.rebuild_active_access();
-
         // SAFETY:
         // - `finish_system_and_handle_dependents` has updated the currently running systems.
         // - `rebuild_active_access` locks access for all currently running systems.
@@ -488,37 +543,30 @@ impl ExecutorState {
         {
             for condition in &mut conditions.set_conditions[set_idx] {
                 condition.update_archetype_component_access(world);
-                if !condition
+            }
-                    .archetype_component_access()
+            if !self.set_condition_conflicting_systems[set_idx].is_disjoint(&self.running_systems) {
-                    .is_compatible(&self.active_access)
+                return false;
-                {
-                    return false;
-                }
             }
         }
 
         for condition in &mut conditions.system_conditions[system_index] {
             condition.update_archetype_component_access(world);
-            if !condition
+        }
-                .archetype_component_access()
+        if !system_meta
-                .is_compatible(&self.active_access)
+            .condition_conflicting_systems
-            {
+            .is_disjoint(&self.running_systems)
-                return false;
+        {
-            }
+            return false;
         }
 
         if !self.skipped_systems.contains(system_index) {
             system.update_archetype_component_access(world);
-            if !system
+            if !system_meta
-                .archetype_component_access()
+                .conflicting_systems
-                .is_compatible(&self.active_access)
+                .is_disjoint(&self.running_systems)
             {
                 return false;
             }
-
-            self.system_task_metadata[system_index]
-                .archetype_component_access
-                .clone_from(system.archetype_component_access());
         }
 
         true
@@ -648,9 +696,6 @@ impl ExecutorState {
             context.system_completed(system_index, res, system);
         };
 
-        self.active_access
-            .extend(&system_meta.archetype_component_access);
-
         if system_meta.is_send {
             context.scope.spawn(task);
         } else {
@@ -741,15 +786,6 @@ impl ExecutorState {
             }
         }
     }
-
-    fn rebuild_active_access(&mut self) {
-        self.active_access.clear();
-        for index in self.running_systems.ones() {
-            let system_meta = &self.system_task_metadata[index];
-            self.active_access
-                .extend(&system_meta.archetype_component_access);
-        }
-    }
 }
 
 fn apply_deferred(

crates/bevy_ecs/src/system/adapter_system.rs

@@ -131,6 +131,12 @@ where
         self.system.component_access()
     }
 
+    fn component_access_set(
+        &self,
+    ) -> &crate::query::FilteredAccessSet<crate::component::ComponentId> {
+        self.system.component_access_set()
+    }
+
     #[inline]
     fn archetype_component_access(
         &self,

crates/bevy_ecs/src/system/combinator.rs

@@ -5,7 +5,7 @@ use crate::{
     archetype::ArchetypeComponentId,
     component::{ComponentId, Tick},
     prelude::World,
-    query::Access,
+    query::{Access, FilteredAccessSet},
     schedule::InternedSystemSet,
     system::{input::SystemInput, SystemIn, SystemParamValidationError},
     world::unsafe_world_cell::UnsafeWorldCell,
@@ -114,7 +114,7 @@ pub struct CombinatorSystem<Func, A, B> {
     a: A,
     b: B,
     name: Cow<'static, str>,
-    component_access: Access<ComponentId>,
+    component_access_set: FilteredAccessSet<ComponentId>,
     archetype_component_access: Access<ArchetypeComponentId>,
 }
 
@@ -122,13 +122,13 @@ impl<Func, A, B> CombinatorSystem<Func, A, B> {
     /// Creates a new system that combines two inner systems.
     ///
     /// The returned system will only be usable if `Func` implements [`Combine<A, B>`].
-    pub const fn new(a: A, b: B, name: Cow<'static, str>) -> Self {
+    pub fn new(a: A, b: B, name: Cow<'static, str>) -> Self {
         Self {
             _marker: PhantomData,
             a,
             b,
             name,
-            component_access: Access::new(),
+            component_access_set: FilteredAccessSet::default(),
             archetype_component_access: Access::new(),
         }
     }
@@ -148,7 +148,11 @@ where
     }
 
     fn component_access(&self) -> &Access<ComponentId> {
-        &self.component_access
+        self.component_access_set.combined_access()
+    }
+
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        &self.component_access_set
     }
 
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
@@ -211,8 +215,10 @@ where
     fn initialize(&mut self, world: &mut World) {
         self.a.initialize(world);
         self.b.initialize(world);
-        self.component_access.extend(self.a.component_access());
+        self.component_access_set
-        self.component_access.extend(self.b.component_access());
+            .extend(self.a.component_access_set().clone());
+        self.component_access_set
+            .extend(self.b.component_access_set().clone());
     }
 
     fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
@@ -343,7 +349,7 @@ pub struct PipeSystem<A, B> {
     a: A,
     b: B,
     name: Cow<'static, str>,
-    component_access: Access<ComponentId>,
+    component_access_set: FilteredAccessSet<ComponentId>,
     archetype_component_access: Access<ArchetypeComponentId>,
 }
 
@@ -354,12 +360,12 @@ where
     for<'a> B::In: SystemInput<Inner<'a> = A::Out>,
 {
     /// Creates a new system that pipes two inner systems.
-    pub const fn new(a: A, b: B, name: Cow<'static, str>) -> Self {
+    pub fn new(a: A, b: B, name: Cow<'static, str>) -> Self {
         Self {
             a,
             b,
             name,
-            component_access: Access::new(),
+            component_access_set: FilteredAccessSet::default(),
             archetype_component_access: Access::new(),
         }
     }
@@ -379,7 +385,11 @@ where
     }
 
     fn component_access(&self) -> &Access<ComponentId> {
-        &self.component_access
+        self.component_access_set.combined_access()
+    }
+
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        &self.component_access_set
     }
 
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
@@ -443,8 +453,10 @@ where
     fn initialize(&mut self, world: &mut World) {
         self.a.initialize(world);
         self.b.initialize(world);
-        self.component_access.extend(self.a.component_access());
+        self.component_access_set
-        self.component_access.extend(self.b.component_access());
+            .extend(self.a.component_access_set().clone());
+        self.component_access_set
+            .extend(self.b.component_access_set().clone());
     }
 
     fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {

crates/bevy_ecs/src/system/exclusive_function_system.rs

@@ -1,7 +1,7 @@
 use crate::{
     archetype::ArchetypeComponentId,
     component::{ComponentId, Tick},
-    query::Access,
+    query::{Access, FilteredAccessSet},
     schedule::{InternedSystemSet, SystemSet},
     system::{
         check_system_change_tick, ExclusiveSystemParam, ExclusiveSystemParamItem, IntoSystem,
@@ -86,6 +86,11 @@ where
         self.system_meta.component_access_set.combined_access()
     }
 
+    #[inline]
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        &self.system_meta.component_access_set
+    }
+
     #[inline]
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
         &self.system_meta.archetype_component_access

crates/bevy_ecs/src/system/function_system.rs

@@ -693,6 +693,11 @@ where
         self.system_meta.component_access_set.combined_access()
     }
 
+    #[inline]
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        &self.system_meta.component_access_set
+    }
+
     #[inline]
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
         &self.system_meta.archetype_component_access

crates/bevy_ecs/src/system/observer_system.rs

@@ -7,7 +7,7 @@ use crate::{
     error::Result,
     never::Never,
     prelude::{Bundle, Trigger},
-    query::Access,
+    query::{Access, FilteredAccessSet},
     schedule::{Fallible, Infallible},
     system::{input::SystemIn, System},
     world::{unsafe_world_cell::UnsafeWorldCell, DeferredWorld, World},
@@ -122,6 +122,11 @@ where
         self.observer.component_access()
     }
 
+    #[inline]
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        self.observer.component_access_set()
+    }
+
     #[inline]
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
         self.observer.archetype_component_access()

crates/bevy_ecs/src/system/schedule_system.rs

@@ -4,7 +4,7 @@ use crate::{
     archetype::ArchetypeComponentId,
     component::{ComponentId, Tick},
     error::Result,
-    query::Access,
+    query::{Access, FilteredAccessSet},
     system::{input::SystemIn, BoxedSystem, System},
     world::{unsafe_world_cell::UnsafeWorldCell, DeferredWorld, World},
 };
@@ -36,6 +36,11 @@ impl<S: System<In = ()>> System for InfallibleSystemWrapper<S> {
     }
 
     #[inline]
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId> {
+        self.0.component_access_set()
+    }
+
+    #[inline(always)]
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
         self.0.archetype_component_access()
     }

crates/bevy_ecs/src/system/system.rs

@@ -9,7 +9,7 @@ use thiserror::Error;
 use crate::{
     archetype::ArchetypeComponentId,
     component::{ComponentId, Tick},
-    query::Access,
+    query::{Access, FilteredAccessSet},
     schedule::InternedSystemSet,
     system::{input::SystemInput, SystemIn},
     world::{unsafe_world_cell::UnsafeWorldCell, DeferredWorld, World},
@@ -44,8 +44,13 @@ pub trait System: Send + Sync + 'static {
     fn type_id(&self) -> TypeId {
         TypeId::of::<Self>()
     }
+
     /// Returns the system's component [`Access`].
     fn component_access(&self) -> &Access<ComponentId>;
+
+    /// Returns the system's component [`FilteredAccessSet`].
+    fn component_access_set(&self) -> &FilteredAccessSet<ComponentId>;
+
     /// Returns the system's archetype component [`Access`].
     fn archetype_component_access(&self) -> &Access<ArchetypeComponentId>;
     /// Returns true if the system is [`Send`].

release-content/migration-guides/remove_archetypecomponentid.md

@@ -0,0 +1,19 @@
+---
+title: Remove `ArchetypeComponentId`
+pull_requests: [16885]
+---
+
+The schedule will now prevent systems from running in parallel if there *could* be an archetype that they conflict on, even if there aren't actually any.  For example, these systems will now conflict even if no entity has both `Player` and `Enemy` components:
+
+```rust
+fn player_system(query: Query<(&mut Transform, &Player)>) {}
+fn enemy_system(query: Query<(&mut Transform, &Enemy)>) {}
+```
+
+To allow them to run in parallel, use `Without` filters, just as you would to allow both queries in a single system:
+
+```rust
+// Either one of these changes alone would be enough
+fn player_system(query: Query<(&mut Transform, &Player), Without<Enemy>>) {}
+fn enemy_system(query: Query<(&mut Transform, &Enemy), Without<Player>>) {}
+```