Editor causing ECS crash

I get a crash that seems to be dependent on the way that the code is run in the Editor.

When I click Play the first time my game runs just fine. When I stop the game and run it a second time it crashes when I try to call CreateEntity on EntityCommanBuffer:

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. Unity.Entities.ComponentChunkIterator.UpdateCacheToCurrentChunk (Unity.Entities.ComponentChunkCache& cache, System.Boolean isWriting, System.Int32 indexInComponentGroup) (at Library/PackageCache/com.unity.entities@0.0.12-preview.19/Unity.Entities/Iterators/ComponentChunkIterator.cs:368)
3. Unity.Entities.ComponentChunkIterator.MoveToEntityIndexAndUpdateCache (System.Int32 index, Unity.Entities.ComponentChunkCache& cache, System.Boolean isWriting) (at Library/PackageCache/com.unity.entities@0.0.12-preview.19/Unity.Entities/Iterators/ComponentChunkIterator.cs:387)
4. Unity.Entities.EntityArray.get_Item (System.Int32 index) (at Library/PackageCache/com.unity.entities@0.0.12-preview.19/Unity.Entities/Iterators/EntityArray.cs:46)
5. ECS.Systems.Board.BoardAttachSystem.OnUpdate () (at Assets/Scripts/ECS/Systems/Board/BoardAttachSystem.cs:30)
6. Unity.Entities.ComponentSystem.InternalUpdate () (at Library/PackageCache/com.unity.entities@0.0.12-preview.19/Unity.Entities/ComponentSystem.cs:374)
7. Unity.Entities.ScriptBehaviourManager.Update () (at Library/PackageCache/com.unity.entities@0.0.12-preview.19/Unity.Entities/ScriptBehaviourManager.cs:77)
8. Unity.Entities.ScriptBehaviourUpdateOrder+DummyDelagateWrapper.TriggerUpdate () (at Library/PackageCache/com.unity.entities@0.0.12-preview.19/Unity.Entities/ScriptBehaviourUpdateOrder.cs:703)
9.  

This will happen over and over again until i restart Unity. Changing the scenes doesn't help

 

I ran into this issue too, although in a totally different use case from an EntityCommandBuffer.

This code breaks after the first run:

Code (CSharp):

1. public Entity GetFirstEntity(ComponentGroup group)
2.         {
3.             var entities = group.GetEntityArray();
4.             if (entities.Length <= 0)
5.             {
6.                 throw new InvalidOperationException($"Failed to find an entity in {group}");
7.             }
8.             return entities[0];
9.         }

This alternative code works pretty consistently:

Code (CSharp):

1. public Entity GetFirstEntity(ComponentGroup group)
2.         {
3.             if (group.CalculateLength() <= 0)
4.             {
5.                 throw new InvalidOperationException($"Failed to find an entity in {group}");
6.             }
7.  
8.             var entityType = GetArchetypeChunkEntityType();
9.             var chunks = group.CreateArchetypeChunkArray(Allocator.Temp);
10.             var entities = chunks[0].GetNativeArray(entityType);
11.             var entity = entities[0];
12.             chunks.Dispose();
13.             return entity;
14.         }

EntityArray seems to be the culprit. Note that I am using a custom world and manually creating and updating systems.

 

@DreamingImLatios Uh, yes, I forgot to add this. I was using ComponentGroups. Today I moved all of my systems to using [Inject] and everything works fine.

 

Just an FYI, there was a UniteLA talk and a forum thread about deprecating injection dependencies.

https://forum.unity.com/threads/api-usability.550450/#post-3676813

 

@psuong That's why I was using ComponentGroups in the first place. Once we get a properly working alternative I'll move from [Inject]. Translating between [Inject] method and ComponentGroups is pretty straightforward

 

CG and Chunk Iteration works perfectly, and I think problem in your logic, but without any context no one can help to solve it

 

@eizenhorn See the code example in the second comment ( by @DreamingImLatios ). The exact same thing is happening for me. Whenever I use ComponentGroup.GetEntityArray() I get crashes on EntityCommandBuffer.CreateEntity() in a subsequent launches in GameMode

 

Again - there is NO some context.
Just for show you, write simple system which creates command buffers and gets entities array from group many times.

Code (CSharp):

1. public struct SomeComponent : IComponentData
2. {
3.     public int Value;
4. }
5.  
6. [AlwaysUpdateSystem]
7. public class TestSystem : JobComponentSystem
8. {
9.     private ComponentGroup someGroup;
10.     private TestSystemBarrier barrier;
11.  
12.     protected override void OnCreateManager()
13.     {
14.         barrier = World.GetOrCreateManager<TestSystemBarrier>();
15.         someGroup = GetComponentGroup(typeof(SomeComponent));
16.     }
17.  
18.     public struct TestParallelJob : IJobParallelFor
19.     {
20.         public EntityCommandBuffer.Concurrent ecb;
21.  
22.         public void Execute(int index)
23.         {
24.             ecb.CreateEntity(index);
25.             ecb.AddComponent(index, new SomeComponent()
26.             {
27.                 Value = index
28.             });
29.         }
30.     }
31.  
32.     protected override JobHandle OnUpdate(JobHandle inputDeps)
33.     {
34.         if (Input.GetKeyDown(KeyCode.Space))
35.         {
36.             inputDeps.Complete();
37.  
38.             Debug.Log("Check entity array exists");
39.             EntityArray entities = someGroup.GetEntityArray();
40.             if (entities.Length == 0)
41.             {
42.                 Debug.Log("Entities not wxists. Create 10 entities from parallel job!");
43.                 TestParallelJob job = new TestParallelJob()
44.                 {
45.                     ecb = barrier.CreateCommandBuffer().ToConcurrent()
46.                 };
47.                 job.Schedule(10, 10).Complete();
48.             }
49.             else
50.             {
51.                 Debug.Log($"{entities.Length} entities exists! Try get entities again!");
52.                 EntityArray entities2 = someGroup.GetEntityArray();
53.                 Debug.Log($"And again {entities2.Length} exists!");
54.             }
55.      
56.         }
57.  
58.         return inputDeps;
59.     }
60. }

All works as expected, after first run, second run and other. With check on space pressed,


without check space pressed (logging every frame)


Also all works fine if create system manually

Code (CSharp):

1. public class TestSystem : MonoBehaviour
2. {
3.     private TestJobSystem _jobsystem;
4.  
5.     private void Update()
6.     {
7.         if (Input.GetKeyDown(KeyCode.C))
8.         {
9.             _jobsystem = World.Active.GetOrCreateManager<TestJobSystem>();
10.             ScriptBehaviourUpdateOrder.UpdatePlayerLoop(World.Active);
11.         }
12.     }
13. }
14.  
15. public struct SomeComponent : IComponentData
16. {
17.     public int Value;
18. }
19.  
20. [DisableAutoCreation, AlwaysUpdateSystem]
21. public class TestJobSystem : JobComponentSystem
22. {
23.     private ComponentGroup _someGroup;
24.     private TestJobSystemBarrier _barrier;
25.  
26.     protected override void OnCreateManager()
27.     {
28.         Debug.Log("Created!");
29.         _barrier = World.GetOrCreateManager<TestJobSystemBarrier>();
30.         _someGroup = GetComponentGroup(typeof(SomeComponent));
31.     }
32.  
33.     public struct TestParallelJob : IJobParallelFor
34.     {
35.         public EntityCommandBuffer.Concurrent ecb;
36.  
37.         public void Execute(int index)
38.         {
39.             ecb.CreateEntity(index);
40.             ecb.AddComponent(index, new SomeComponent()
41.             {
42.                 Value = index
43.             });
44.         }
45.     }
46.  
47.     protected override JobHandle OnUpdate(JobHandle inputDeps)
48.     {
49.         inputDeps.Complete();
50.  
51.         Debug.Log("Check entity array exists");
52.         EntityArray entities = _someGroup.GetEntityArray();
53.         if (entities.Length == 0)
54.         {
55.             Debug.Log("Entities not wxists. Create 10 entities from parallel job!");
56.             TestParallelJob job = new TestParallelJob()
57.             {
58.                 ecb = _barrier.CreateCommandBuffer().ToConcurrent()
59.             };
60.             job.Schedule(10, 10).Complete();
61.         }
62.         else
63.         {
64.             Debug.Log($"{entities.Length} entities exists! Try get entities again!");
65.             EntityArray entities2 = _someGroup.GetEntityArray();
66.             Debug.Log($"And again {entities2.Length} exists!");
67.         }
68.  
69.         return inputDeps;
70.     }
71. }
72.  
73. [UpdateAfter(typeof(TestJobSystem))]
74. public class TestJobSystemBarrier : BarrierSystem
75. {
76.  
77. }

 

The errors come from indexing EntityArray using the index operator [].

 

No. Indexing works fine.



And all works as expected without errors after many Play\Unplay loops

 

@eizenhorn Yeah, you're right. I'll try to provide a repo with a minimal project reproducing the crash this weekend