Question NullReferenceException in ArchetypeChunk when scheduling an IJobEntityBatchWithIndex

hi,

I'm trying to change the number of batches when scheduling an IJobEntityBatchWithIndex.
Goal is to run an expansive job in parralel over a small number of chunk and entities.
However, when I change the number of batchesPerChunk for a number > 1, I get the following error :

NullReferenceException: Object reference not set to an instance of an object

Unity.Entities.ArchetypeChunk.get_Count () (at Library/PackageCache/com.unity.entities@0.17.0-preview.42/Unity.Entities/Iterators/ArchetypeChunkArray.cs:34)

Unity.Entities.JobEntityBatchIndexExtensions+JobEntityBatchIndexProducer`1[T].ExecuteInternal (Unity.Entities.JobEntityBatchIndexExtensions+JobEntityBatchIndexWrapper`1[T]& jobWrapper, System.IntPtr bufferRangePatchData, Unity.Jobs.LowLevel.Unsafe.JobRanges& ranges, System.Int32 jobIndex) (at Library/PackageCache/com.unity.entities@0.17.0-preview.42/Unity.Entities/IJobEntityBatchWithIndex.cs:587)

Unity.Entities.JobEntityBatchIndexExtensions+JobEntityBatchIndexProducer`1[T].Execute (Unity.Entities.JobEntityBatchIndexExtensions+JobEntityBatchIndexWrapper`1[T]& jobIndexWrapper, System.IntPtr additionalPtr, System.IntPtr bufferRangePatchData, Unity.Jobs.LowLevel.Unsafe.JobRanges& ranges, System.Int32 jobIndex) (at Library/PackageCache/com.unity.entities@0.17.0-preview.42/Unity.Entities/IJobEntityBatchWithIndex.cs:558)

My guess is something to deal with the archetype modification (RemoveComponent)
Does anyone have an idea of how I can avoid this error ? maybe it's a dependencies issues ?

Here, a simple example of how reproduce my issue.

Code (CSharp):

1. using UnityEngine;
2. using Unity.Entities;
3.  
4. public class Example : MonoBehaviour
5. {
6.     private Entity[] entities;
7.     private int entityCount = 10;
8.     private EntityManager em;
9.     void Start()
10.     {
11.         entities = new Entity[entityCount];
12.         em = World.DefaultGameObjectInjectionWorld.EntityManager;
13.         for (int i = 0; i < entityCount; i++)
14.         {
15.             entities[i] = World.DefaultGameObjectInjectionWorld.EntityManager.CreateEntity();
16.             em.AddComponent<IsActive>(entities[i]);
17.         }
18.     }
19.     void Update()
20.     {
21.         int randomIndex = Random.Range(0, entityCount - 1);
22.         // remove one entity of the archetype
23.         em.RemoveComponent<IsActive>(entities[randomIndex]);
24.     }
25. }
26.  
27. public struct IsActive : IComponentData { }
28.  
29.  
30. public class MySystem : SystemBase
31. {
32.     private BeginSimulationEntityCommandBufferSystem ecbSystem;
33.     private EntityQueryDesc entityQueryDesc;
34.     private EntityQuery entityQuery;
35.    
36.     protected override void OnCreate()
37.     {
38.         ecbSystem = World.GetOrCreateSystem<BeginSimulationEntityCommandBufferSystem>();
39.         base.OnCreate();
40.  
41.         entityQueryDesc = new EntityQueryDesc
42.         {
43.             All = new ComponentType[] { typeof(IsActive) }
44.         };
45.  
46.         entityQuery = World.DefaultGameObjectInjectionWorld.EntityManager.CreateEntityQuery(entityQueryDesc);    
47.     }
48.  
49.     protected override void OnUpdate()
50.     {
51.         Debug.Log(entityQuery.CalculateChunkCount());
52.         Debug.Log(entityQuery.CalculateEntityCount());
53.  
54.         var job = new MyVeryExpansiveJob();
55.  
56.         this.Dependency = job.ScheduleParallel(entityQuery, 4, this.Dependency);
57.         ecbSystem.AddJobHandleForProducer(this.Dependency);
58.     }
59. }
60.  
61.  
62. public struct MyVeryExpansiveJob : IJobEntityBatchWithIndex
63. {
64.     public void Execute(ArchetypeChunk batchInChunk, int batchIndex, int indexOfFirstEntityInQuery)
65.     {
66.         // nothing particular
67.     }
68. }

I'm using unity.entities 0.17.0-preview42

thank you in advance !

 

I got the same error when I tried with a batchCount > 1. Think it's just bugged.

 

I have encountered the same bug and your code sample reproduces it indeed.
I may have fixed it as follow :

Code (CSharp):

1.  
2. public struct MyVeryExpansiveJob : IJobParallelFor
3. {
4.     public ArchetypeChunk chunk;
5.     public void Execute(int index)
6.     {
7.         // nothing particular
8.     }
9. }

And in MySystem :

Code (CSharp):

1. protected override void OnUpdate()
2.     {
3.         Debug.Log(entityQuery.CalculateChunkCount());
4.         Debug.Log(entityQuery.CalculateEntityCount());
5.  
6.         NativeArray<ArchetypeChunk> chunkArchetypes = GetEntityQuery(typeof(IsActive)).CreateArchetypeChunkArray(Unity.Collections.Allocator.Temp);
7.  
8.         int nbatch = 1;
9.         foreach (ArchetypeChunk chunk in chunkArchetypes) {
10.             new MyVeryExpansiveJob() {
11.                 chunk = chunk
12.             }.Schedule(chunk.ChunkEntityCount, chunk.ChunkEntityCount/nbatch);
13.         }
14.         chunkArchetypes.Dispose();
15.     }

nbatch is the number of batch that you want, to match your sample code you would set it to 4.

 

Same. This helps!