EntityManager operations not allowed in ForEach when looping DynamicBuffer

The 0.1.0 patch notes mentioned:

However, when EntityManager is used inside a DynamicBuffer `foreach`, I get the following error:

This is the code to reproduce:

Code (CSharp):

1. using Unity.Entities;
2.  
3. public struct Tag : IComponentData
4. {
5. }
6.  
7. [InternalBufferCapacity(4)]
8. public struct BufferData : IBufferElementData
9. {
10.     public float Value;
11. }
12.  
13. public class TestSystem : ComponentSystem
14. {
15.     protected override void OnUpdate()
16.     {
17.         Entities.ForEach((Entity entity, DynamicBuffer<BufferData> buffer) =>
18.         {
19.             foreach (BufferData bufferData in buffer)
20.             {
21.                 if (!EntityManager.HasComponent<Tag>(entity))
22.                 {
23.                     EntityManager.AddComponentData(entity, new Tag());
24.                 }
25.             }
26.         });
27.     }
28. }

The DynamicBuffer is filled with 4 values at entity conversion time. Is this error by design or a bug?

 

Tested your code and can confirm. After the

EntityManager.AddComponentData

,

buffer

will be deallocated. Should be a bug.

For the time being, you'll have to keep doing

EntityManager.GetBuffer<BufferData>(entity)

after every structural change.

 

Can you update with bug report if you file one. I would love to track this

 

I sent a bug report a couple hours ago: https://fogbugz.unity3d.com/default.asp?1185212_umgejlaka8ub07ua

 

Pretty sure this is by design.

DynamicBuffer is a pointer to an array (usually stored inline in the chunk). When you add the Tag component you move the entity and its components (including the array) to another archetype/chunk, but the pointer still points to the old location, so it is correctly recognized as invalid.
Could use a better error message I guess.

 

But isn't it the same with all EntityManager operations inside a ForEach? To me it's weird that the new version handles only some of the chunk-altering methods.

 

The new (post-0.1.0) ForEach is more or less:

Code (CSharp):

1. var query = PrepareQuery();
2. var entities = query.ToEntityArray();
3. foreach (var entity in entities) {
4.     var copy1 = GetComponent<SecondLambdaArg>(entity);
5.     lambda(entity, ref copy1);
6.     if (HasComponent<SecondLambdaArg>(entity)){
7.         SetComponent(entity, copy1);
8.     }
9. }

Entities are stable across structural changes and all their components are copied locally in the ForEach to make the ref stable.

 

Okay that makes sense. For perf reasons, probably not a good idea to also copy buffers around.

 

I had the same issue and got that error today.

JPrzemieniecki is right, it's an error by design.

You can copy the buffer to a NativeArray using buffer.ToNativeArray and keep your code design using the EntityManager inside the loop without errors.

 

Thanks everyone, this makes sense!