Bug DynamicBuffer broken in context of Entities.WithStructuralChanges

This bug is biting me really hard today.

When accessing a DynamicBuffer in an Entities.WithStructuralChanges.ForEach, I get the error:
The NativeArray has been deallocated, it is not allowed to access it, when trying to access the DynamicBuffer.

Here's a dirt-simple repro:

Code (CSharp):

1. using Unity.Burst;
2. using Unity.Collections;
3. using Unity.Entities;
4. using Unity.Jobs;
5. using Unity.Mathematics;
6. using Unity.Transforms;
7.  
8. [GenerateAuthoringComponent]
9. public struct Spawner : IComponentData
10. {
11.     public Entity prefab;
12. }
13.  
14. public struct FactionMember : ISharedComponentData
15. {
16.     public Entity entity;
17. }
18.  
19. public class SpawnSystem : SystemBase
20. {
21.     protected override void OnUpdate()
22.     {
23.         Entities.WithStructuralChanges().ForEach((Entity entity, in Spawner spawner) =>
24.         {
25.             var factionMember = new FactionMember { entity = entity };
26.             var firstInstance                              = EntityManager.Instantiate(spawner.prefab);
27.             var linkedGroup                                = EntityManager.GetBuffer<LinkedEntityGroup>(firstInstance);
28.             foreach (var e in linkedGroup)
29.             {
30.                 EntityManager.AddSharedComponentData(e.Value, factionMember);
31.             }
32.             if (!EntityManager.HasComponent<FactionMember>(firstInstance))
33.                 EntityManager.AddSharedComponentData(firstInstance, factionMember);
34.         }).Run();
35.         EntityManager.RemoveComponent<Spawner>(EntityManager.UniversalQuery);
36.     }
37. }
38.  
39.  

Uploading bug report as I create this thread.

 

As far as I'm aware this technically isn't a bug just how it's always worked. Pretty certain it's mentioned in the documentation somewhere.

Any structural to entity manager will invalidate all dynamic buffers

The only way around it is to copy your buffer to an array or use a local ECB and just play it back after the job instead of using structural changes

 

Yeah here it is

https://docs.unity3d.com/Packages/com.unity.entities@0.11/manual/sync_points.html

Structural changes not only require a sync point, but they also invalidate all direct references to any component data. This includes instances of DynamicBuffer and the result of methods that provide direct access to the components such as ComponentSystemBase.GetComponentDataFromEntity.

 

Yup. I see that behavior now. The actual test case I had made it seem like the buffer was being invalidated before I was even making structural changes, but looking back that wasn't actually the case.

Unfortunately an ECB doesn't work here because the use case is Instantiate, Add SharedComponent, and then Instantiate many. Copying to array seems like a good workaround though.

 

Thanks for this info guys. You would think that in 1.0 specifying the read-only parameter to true in SystemAPI.GetSingletonBuffer<MyData>(true) would avoid this error, but nope - we still need to copy to array or use ECB.