Unity locks up when creating multiple Attach components

I have encountered a strange issue that crashes Unity every time I try to instantiate a zombie. The code that I added is below. Basically all I'm trying to do is look through all of the zombies subcomponents for a GameObjectEntity and then using the AttachComponent to mark the root entity as it's parent.

Perhaps I'm doing something I shouldn't be doing and I can do it differently w/ ECS. What I'm trying to accomplish is this - the zombie prefab has sub-gameobjects with things colliders that need a `TeamComponent` in order to tell if it should deal damage to the thing it's colliding with. There is an ability that allows the player to temporarily 'covert' a zombie to it's side so I need to change out it's `TeamComponent` to be the players `TeamComponent`. When doing this I need to get all of the `TeamComponents` on the zombie and change them all to the players team.

P.S. I'm using Hybrid ECS.

Code (CSharp):

1.            
2. var zombie =  _zombieDiContainer.InstantiatePrefabForComponent<ZombieView>(_settings.ZombiePrefab); //This is basically just a DI way of instantiating a Prefab using Zenject
3. var entityComponent = zombie.GetComponent<GameObjectEntity>();
4. var rootEntity = entityComponent.Entity;
5. var manager = entityComponent.EntityManager;
6.  
7. //Start of new code that locks up Unity
8. var subEntities = zombie.GetComponentsInChildren<GameObjectEntity>().Select(x => x.Entity);
9. foreach (var subEntity in subEntities)
10. {
11.     var attacherEntity = manager.CreateEntity();
12. /* maybe it's crashing due to multiple Attach components pointing to the same Parent? */
13.     manager.AddComponentData(attacherEntity, new Attach
14.     {
15.         Child = subEntity,
16.             Parent = rootEntity
17.     });
18. }
19. // End of the new code
20.  

 

I think your issue is GetComponentsInChildren as it also returns components on the same gameobject

Returns all components of Type type in the GameObject or any of its children.

So it's also trying to make zombie a child of itself.

e.g. it ends up being

Code (CSharp):

1. new Attach {
2.     Child = rootEntity,
3.     Parent = rootEntity,
4. }

which I suspect unity does not like.

You need to filter out the root.

 

That fixed it. Thanks @tertle !

 

@tertle - while your suggestion fixed the issue I was having it revealed that my thinking is off. It looks like the child components get a Parent component. Do you know - is there any way to go from Parent to Children in ECS?

 

No, not yet. I made a similar post months ago when the attached was introduced, but that system hasn't been touched for a while. Joachim has expressed that it would be nice to have an API layer method of traversing the hierarchy though.

My guess: GDC will be their next big push. :\

 

I created a quick system that adds a

DynamicBuffer

to the Parent entity with all of it's children. Here is the code if anyone is interested. Let me know if there is a better way to do it. Perhaps a way using

IJobChunk

or something?

Code (CSharp):

1.  
2. using Unity.Burst;
3. using Unity.Collections;
4. using Unity.Entities;
5. using Unity.Jobs;
6. using Unity.Transforms;
7.  
8. public struct Children : IBufferElementData
9. {
10.     public Entity Child;
11.  
12.     public static implicit operator Entity(Children child) => child.Child;
13.     public static implicit operator Children(Entity entity) => new Children { Child = entity };
14. }
15.  
16. [UpdateBefore(typeof(TransformSystem))]
17. [BurstCompile]
18. public class BuildChildArraySystem : JobComponentSystem
19. {
20.     private ComponentGroup _filter;
21.  
22.     protected override void OnCreateManager()
23.     {
24.         _filter = GetComponentGroup(new EntityArchetypeQuery()
25.         {
26.             All = new ComponentType[] { typeof(Attach) },
27.             Any = new ComponentType[] { },
28.             None = new ComponentType[] { },
29.         });
30.     }
31.  
32.     protected override JobHandle OnUpdate(JobHandle inputDeps)
33.     {
34.         var filterChunks = _filter.CreateArchetypeChunkArray(Allocator.TempJob);
35.         var attachType = GetArchetypeChunkComponentType<Attach>();
36.         foreach (var chunk in filterChunks)
37.         {
38.             foreach (var attachComponent in chunk.GetNativeArray(attachType))
39.             {
40.                 if (!EntityManager.HasComponent<Children>(attachComponent.Parent)){
41.                     EntityManager.AddBuffer<Children>(attachComponent.Parent);
42.                 }
43.  
44.                 var buffer = EntityManager.GetBuffer<Children>(attachComponent.Parent);
45.                 buffer.Add(attachComponent.Child);
46.             }
47.         }
48.  
49.         filterChunks.Dispose();
50.         return inputDeps;
51.     }
52. }
53.  
54.  

 

Just to add another solution, there is a parent to child multihashmap in TransformSystem, which can be retrieved with reflection. This is a system I use to destroy an entire hierarchy:

Code (CSharp):

1. [UpdateAfter(typeof(TransformSystem))]
2. [UpdateBefore(typeof(EndFrameBarrier))]
3. public class DestroyHierarchySystem : JobComponentSystem {
4.     [Inject] EndFrameBarrier barrier;
5.     bool isInitialized;
6.     NativeMultiHashMap<Entity, Entity> parentToChildTree;
7.  
8.     void Init() {
9.         //Using reflection to get the existing ParentToChildTree HashMap of TransformSystem.
10.         var transformSystem = World.GetExistingManager<TransformSystem>();
11.         var parentToChildInfo = typeof(TransformSystem).GetField(
12.             "ParentToChildTree", BindingFlags.NonPublic | BindingFlags.Instance);
13.         parentToChildTree = (NativeMultiHashMap<Entity, Entity>)parentToChildInfo.GetValue(transformSystem);
14.         isInitialized = true;
15.     }
16.  
17.     [BurstCompile]
18.     struct DestroyHierarchyJob : IJobProcessComponentDataWithEntity<DestroyEntityTag> {
19.         public EntityCommandBuffer.Concurrent CommandBuffer;
20.         [ReadOnly] public NativeMultiHashMap<Entity, Entity> ParentToChildTree;
21.         [ReadOnly] public ComponentDataFromEntity<DestroyEntityTag> DestroyEntityTags;
22.      
23.         public void Execute(Entity entity, int jobIndex, [ReadOnly] ref DestroyEntityTag tag) {
24.             DestroyTreeIterative(jobIndex, entity);
25.         }
26.      
27.         void DestroyTreeIterative(int jobIndex, Entity parent) {
28.             CommandBuffer.DestroyEntity(jobIndex, parent);
29.             if(!ParentToChildTree.TryGetFirstValue(parent, out Entity foundChild, out var iterator)) {
30.                 return;
31.             }
32.             do {
33.                 DestroyTreeIterative(jobIndex, foundChild);
34.                 //Check that child does not already have a tag so it is not deleted twice.
35.                 if(!DestroyEntityTags.Exists(foundChild)) {
36.                     CommandBuffer.DestroyEntity(jobIndex, foundChild);
37.                 }
38.             } while(ParentToChildTree.TryGetNextValue(out foundChild, ref iterator));
39.         }
40.     }
41.  
42.     protected override JobHandle OnUpdate(JobHandle inputDeps) {
43.         if(!isInitialized) {
44.             Init();
45.         }
46.         return new DestroyHierarchyJob {
47.             CommandBuffer = barrier.CreateCommandBuffer().ToConcurrent(),
48.             ParentToChildTree = parentToChildTree,
49.             DestroyEntityTags = GetComponentDataFromEntity<DestroyEntityTag>(isReadOnly:true)
50.         }.Schedule(this, inputDeps);
51.     }
52. }

I add a DestroyEntityTag at the level I want and destroy the relevant entities, TransformSystem will clean up the hashmap the next time it runs.