Add stable legion entity ids (GuidEntityAllocator)

crates/bevy_legion/legion_core/Cargo.toml

@@ -28,6 +28,7 @@ crossbeam-channel = "0.4.2"
 derivative = "2.1"
 smallvec = "1.4"
 tracing = "0.1"
+rand = "0.7.2"
 metrics = { version = "0.12", optional = true }
 serde = { version = "1", optional = true }
 fxhash = "0.2"

crates/bevy_legion/legion_core/src/command.rs

@@ -1,7 +1,7 @@
 use crate::{
     borrow::AtomicRefCell,
     cons::{ConsAppend, ConsFlatten},
-    entity::{Entity, EntityAllocator},
+    entity::{Entity, GuidEntityAllocator},
     filter::{ChunksetFilterData, Filter},
     storage::{Component, ComponentTypeId, Tag, TagTypeId},
     world::{
@@ -313,7 +313,7 @@ where
 pub struct CommandBuffer {
     world_id: WorldId,
     commands: AtomicRefCell<VecDeque<EntityCommand>>,
-    entity_allocator: Arc<EntityAllocator>,
+    entity_allocator: Arc<GuidEntityAllocator>,
     preallocated_capacity: usize,
     free_list: SmallVec<[Entity; 64]>,
     pending_insertion: SmallVec<[Entity; 64]>,

crates/bevy_legion/legion_core/src/entity.rs

@@ -7,7 +7,7 @@ use std::fmt::Display;
 use std::num::Wrapping;
 use std::ops::Deref;
 use std::ops::DerefMut;
-use std::sync::Arc;
+use std::{collections::HashSet, sync::Arc};
 
 pub type EntityIndex = u32;
 pub(crate) type EntityVersion = Wrapping<u32>;
@@ -20,7 +20,7 @@ pub struct Entity {
 }
 
 impl Entity {
-    pub(crate) fn new(index: EntityIndex, version: EntityVersion) -> Entity {
+    pub fn new(index: EntityIndex, version: EntityVersion) -> Entity {
         Entity { index, version }
     }
 
@@ -247,6 +247,64 @@ impl DerefMut for Blocks {
     fn deref_mut(&mut self) -> &mut Self::Target { self.blocks.deref_mut() }
 }
 
+#[derive(Default, Debug, Clone)]
+pub struct GuidEntityAllocator {
+    entities: Arc<RwLock<HashSet<Entity>>>,
+    next_ids: Arc<RwLock<Vec<Entity>>>,
+}
+
+impl GuidEntityAllocator {
+    pub fn is_alive(&self, entity: Entity) -> bool {
+        self.entities.read().contains(&entity)
+    }
+
+    pub fn push_next_ids(&self, ids: impl Iterator<Item = Entity>) {
+        self.next_ids.write().extend(ids);
+    }
+
+    /// Allocates a new unused `Entity` ID.
+    pub fn create_entity(&self) -> Entity {
+        if !self.next_ids.read().is_empty() {
+            return self.next_ids.write().pop().unwrap();
+        }
+
+        let entity = Entity::new(rand::random::<u32>(), Wrapping(1));
+        self.entities.write().insert(entity);
+        entity
+    }
+
+    /// Creates an iterator which allocates new `Entity` IDs.
+    pub fn create_entities(&self) -> GuidCreateEntityIter {
+        GuidCreateEntityIter {
+            allocator: self,
+        }
+    }
+
+    pub(crate) fn delete_entity(&self, entity: Entity) -> bool {
+        self.entities.write().remove(&entity)
+    }
+
+    pub(crate) fn delete_all_entities(&self) {
+        self.entities.write().clear();
+    }
+
+    pub(crate) fn merge(&self, other: GuidEntityAllocator) {
+        self.entities.write().extend(other.entities.write().drain())
+    }
+}
+
+pub struct GuidCreateEntityIter<'a> {
+    allocator: &'a GuidEntityAllocator
+}
+
+impl<'a> Iterator for GuidCreateEntityIter<'a> {
+    type Item = Entity;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        Some(self.allocator.create_entity())
+    }
+}
+
 /// Manages the allocation and deletion of `Entity` IDs within a world.
 #[derive(Debug)]
 pub struct EntityAllocator {

crates/bevy_legion/legion_core/src/serialize/de.rs

@@ -1,5 +1,5 @@
 use crate::{
-    entity::{Entity, EntityAllocator},
+    entity::{Entity, GuidEntityAllocator},
     index::{ArchetypeIndex, ChunkIndex, SetIndex},
     storage::{
         ArchetypeData, ArchetypeDescription, Chunkset, ComponentMeta, ComponentTypeId, TagMeta,
@@ -78,7 +78,7 @@ pub trait WorldDeserializer {
     fn deserialize_entities<'de, D: Deserializer<'de>>(
         &self,
         deserializer: D,
-        entity_allocator: &EntityAllocator,
+        entity_allocator: &GuidEntityAllocator,
         entities: &mut Vec<Entity>,
     ) -> Result<(), <D as Deserializer<'de>>::Error>;
 }

crates/bevy_legion/legion_core/src/world.rs

@@ -2,9 +2,8 @@ use crate::borrow::Ref;
 use crate::borrow::RefMut;
 use crate::entity::BlockAllocator;
 use crate::entity::Entity;
-use crate::entity::EntityAllocator;
 use crate::entity::EntityLocation;
-use crate::entity::Locations;
+use crate::entity::{GuidEntityAllocator, Locations};
 use crate::event::Event;
 use crate::filter::ArchetypeFilterData;
 use crate::filter::ChunksetFilterData;
@@ -75,7 +74,7 @@ impl Universe {
     /// unique `Entity` IDs, even across worlds. See also `World::new`.
     pub fn create_world(&self) -> World {
         let id = WorldId::next(self.id.0);
-        let world = World::new_in_universe(id, EntityAllocator::new(self.allocator.clone()));
+        let world = World::new_in_universe(id, GuidEntityAllocator::default());
 
         info!(universe = self.id.0, world = world.id().1, "Created world");
         world
@@ -99,7 +98,7 @@ impl WorldId {
 pub struct World {
     id: WorldId,
     storage: UnsafeCell<Storage>,
-    pub(crate) entity_allocator: Arc<EntityAllocator>,
+    pub(crate) entity_allocator: Arc<GuidEntityAllocator>,
     entity_locations: Locations,
     defrag_progress: usize,
     command_buffer_size: usize,
@@ -120,11 +119,11 @@ impl World {
     pub fn new() -> Self {
         Self::new_in_universe(
             WorldId::next(0),
-            EntityAllocator::new(Arc::new(Mutex::new(BlockAllocator::new()))),
+            GuidEntityAllocator::default(),
         )
     }
 
-    fn new_in_universe(id: WorldId, allocator: EntityAllocator) -> Self {
+    fn new_in_universe(id: WorldId, allocator: GuidEntityAllocator) -> Self {
         Self {
             id,
             storage: UnsafeCell::new(Storage::new(id)),

crates/bevy_legion/readme.md

@@ -22,6 +22,7 @@ Here are the changes made:
 * ResourceTypeId, ComponentTypeId, TagTypeId use static str (std::any::type_name) instead of TypeId (std::any::TypeId is not constant across rust binaries) 
 * Implement "DowncastTypeName" to allow downcasting based on type name
 * Upgraded derivative, smallvec, itertools to eliminate redundant dependencies
+* Added GuidEntityAllocator. Generates random entityids and enables "stable" ids across serialization.
 
 ## Benchmarks