nullreferenceexception in CreateEntityQuery?

During dispose of a MonoBehavior object, I'm doing an entity query driven destroy, and i'm getting a null reference exception inside CreateEntityQuery. How can that happen?

This is my destroy.... how can that throw an exception?

Code (Csharp):

1. void DestroyParticleAndContraintEntities() {
2.       if (Entity == null) {
3.         Debug.Assert(Entity!=null,"ClothAuthoring dispose... Entity already null");
4.         return;
5.       }
6.       using (var query = EntityManager.CreateEntityQuery(typeof(ClothChild))) {
7.         query.SetSharedComponentFilter(new ClothChild { ClothEntity = Entity });
8.         EntityManager.DestroyEntity(query);
9.       }
10.     }

Code (csharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. Unity.Collections.LowLevel.Unsafe.UnsafeMultiHashMap`2[TKey,TValue].TryGetFirstValue (TKey key, TValue& item, Unity.Collections.NativeMultiHashMapIterator`1[TKey]& it) (at Library/PackageCache/com.unity.collections@0.7.1-preview.3/Unity.Collections/UnsafeHashMap.cs:1216)
3. Unity.Entities.EntityQueryManager.CreateEntityQuery (Unity.Entities.EntityComponentStore* entityComponentStore, Unity.Entities.ManagedComponentStore managedComponentStore, Unity.Entities.ArchetypeQuery* query, System.Int32 queryCount, Unity.Entities.ComponentType* component, System.Int32 componentCount) (at Library/PackageCache/com.unity.entities@0.9.0-preview.6/Unity.Entities/Iterators/EntityQueryManager.cs:458)
4. Unity.Entities.EntityQueryManager.CreateEntityQuery (Unity.Entities.EntityComponentStore* entityComponentStore, Unity.Entities.ManagedComponentStore managedComponentStore, Unity.Entities.ComponentType* inRequiredComponents, System.Int32 inRequiredComponentsCount) (at Library/PackageCache/com.unity.entities@0.9.0-preview.6/Unity.Entities/Iterators/EntityQueryManager.cs:418)
5. Unity.Entities.EntityManager.CreateEntityQuery (Unity.Entities.ComponentType[] requiredComponents) (at Library/PackageCache/com.unity.entities@0.9.0-preview.6/Unity.Entities/EntityManagerQuery.cs:23)
6. VSC.ECS.ClothAuthoring.DestroyParticleAndContraintEntities () (at Assets/Scripts/ECS/Authoring/Character/ClothAuthoring.cs:217)
7. VSC.ECS.ClothAuthoring.OnDestroy () (at Assets/Scripts/ECS/Authoring/Character/ClothAuthoring.cs:296)
8.  

 

Are you getting this error when leaving play mode / exiting the game?

Because I'd guess the world has been disposed during shutdown before the OnDestroy is being called.

 

yeah, it's during shutdown...

I guess I need to ignore it? why would the ECS world be torn down before the component objects?

 

Why not? To me it makes more sense.

Some disagree with me, but I believe you should drive gameobject world from ECS world, not in reverse. So if I was referencing gameobjects during a system shutdown and they had already been destroyed, that's going to break instead.