NullReferenceException Trying to Destroy Entities in ComponentGroup?

Good Afternoon!

Can anyone help me understand why all of my attempts to destroy entities obtained via GetComponentGroup results in NullReferenceException errors?

A simple example is found below:

Code (CSharp):

1. using System;
2. using Unity.Entities;
3.  
4. public sealed class PlayerInputCleanupSystem : ComponentSystem {
5.     private EntityManager m;
6.  
7.     private ComponentGroup playerInputGroup;
8.  
9.     protected override void OnCreateManager() {
10.         m = World.Active.GetOrCreateManager<EntityManager>();
11.  
12.         playerInputGroup = GetComponentGroup(
13.             new EntityArchetypeQuery {
14.                 All = new[] {
15.                     ComponentType.Create<PlayerInput>(),
16.                 },
17.                 Any = Array.Empty<ComponentType>(),
18.                 None = Array.Empty<ComponentType>()
19.             }
20.         );
21.     }
22.  
23.     protected override void OnUpdate() {
24.         m.DestroyEntity(playerInputGroup);
25.     }
26. }

Any assistance is greatly appreciated.

Thank you and be well!
- S.

 

Hello!

Additional details:

• Issue does not occur when using [Inject], so it appears to be directly related to use of the ComponentGroup.
• Moving the call to GetComponentGroup to the OnUpdate method resolves the issue, but this strikes me as a bad practice.

Any additional thoughts on the matter are greatly appreciated.

Thank you and be well!
- S.

 

Hello!

Correction. Moving GetComponentGroup to the OnUpdate method decreases the frequency of the issue, but does not resolve it. Using [Inject] does in fact resolve the issue, but obviously that is no long term solution.

I suspect there is an aspect of ComponentGroups or GetComponentGroup that I have missed or misunderstand.

Any clarity on this is much appreciated!

Thank you and be well!
- S.

 

Hello!

I found a solution, but the reason still eludes me. For some reason, creating an Entity in another system was causing this system to fail.

Is there a particular why this would occur?

Thank you and be well!
- S.

 

I think I saw that before, could you post the stack trace showing which line of code in ECS lib that it throws?

 

@5argon,

Certainly!

Firstly, the full script to ensure line-number accuracy:

Code (CSharp):

1. using System;
2. using JetBrains.Annotations;
3.  
4. using Unity.Burst;
5. using Unity.Entities;
6.  
7. [UsedImplicitly]
8. [UpdateAfter(typeof(PlayerPromptInputSystem))]
9. public sealed class PlayerInputCleanupSystem : ComponentSystem {
10.     private EntityManager m;
11.  
12.     private ComponentGroup playerInputGroup;
13.  
14.     protected override void OnCreateManager() {
15.         m = World.Active.GetOrCreateManager<EntityManager>();
16.  
17.         playerInputGroup = GetComponentGroup(
18.             new EntityArchetypeQuery {
19.                 All = new[] {
20.                     ComponentType.Create<PlayerInput>(),
21.                 },
22.                 Any = Array.Empty<ComponentType>(),
23.                 None = Array.Empty<ComponentType>()
24.             }
25.         );
26.     }
27.  
28.     [BurstCompile]
29.     protected override void OnUpdate() {
30.         m.DestroyEntity(playerInputGroup);
31.     }
32. }

And the full stack trace:

Spoiler: Stacktrace

NullReferenceException: Object reference not set to an instance of an objectUnity.Entities.EntityDataManager.TryRemoveEntityId (Unity.Entities.Entity* entities, System.Int32 count, Unity.Entities.ArchetypeManager archetypeManager, Unity.Entities.SharedComponentDataManager sharedComponentDataManager, Unity.Entities.EntityGroupManager groupManager, Unity.Entities.ComponentTypeInArchetype* componentTypeInArchetypeArray) (at Library/PackageCache/com.unity.entities@0.0.12-preview.21/Unity.Entities/EntityDataManager.cs:920)Unity.Entities.EntityManager.DestroyEntity (Unity.Entities.ComponentGroup componentGroupFilter) (at Library/PackageCache/com.unity.entities@0.0.12-preview.21/Unity.Entities/EntityManager.cs:317)PlayerInputCleanupSystem.OnUpdate () (at Assets/_Game/Scripts/Systems/PlayerInputCleanupSystem.cs:30)Unity.Entities.ComponentSystem.InternalUpdate () (at Library/PackageCache/com.unity.entities@0.0.12-preview.21/Unity.Entities/ComponentSystem.cs:375)Unity.Entities.ScriptBehaviourManager.Update () (at Library/PackageCache/com.unity.entities@0.0.12-preview.21/Unity.Entities/ScriptBehaviourManager.cs:77)Unity.Entities.ScriptBehaviourUpdateOrder+DummyDelagateWrapper.TriggerUpdate () (at Library/PackageCache/com.unity.entities@0.0.12-preview.21/Unity.Entities/ScriptBehaviourUpdateOrder.cs:703)

And specifications and packages:

Spoiler: Specifications & Packages

Unity Specifications:

• Unity: 2019.1.0a12
• Operating System: Windows 10 Pro

Packages:

• Burst: preview.39 - 0.2.4
• Collections: preview.10 - 0.0.9
• Entities: preview.21 - 0.0.12
• Incremental Compiler: preview.31 - 0.0.42
• Jobs: preview.5 - 0.0.7
• Mathematics: preview.19 - 0.0.12
• Package Manager UI: 0.0.0

Hope that helps. Thank you so much again!

Be well!
- S.

 

Just FYI. You don't need this row

m = World.Active.GetOrCreateManager<EntityManager>();

all systems has EntityManager property. Also all systems has World property.
Also [BurstCompile] do nothing in this place, it's supported only for job yet.

 

Thank you, @eizenhorn!

Is there no performance benefit to caching the EntityManager?
Also, is it safe to assume that the EntityManager will never be null in a ComponentSystem?

Be well!
- S.

 

No

Yes

 

@eizenhorn,

Duly noted. Thank you.

Be well!
- S.