Intermittent issues with accessing entities in ComponentGroup.GetEntityArray()

I'm having a strange issue when trying to get an entity via entities when using ComponentGroups. Just logging out the entity causes intermittent issues:
After modifying the code in any way (even just adding a debug line) the first run works fine.
If I stop the game and run again it will sometimes either log an entities with an index in the 90,000's+ or will throw a null reference exception. It bounce back and forth between these issues every time I run. Here is the exception:

NullReferenceException: Object reference not set to an instance of an object
Unity.Entities.ComponentChunkIterator.UpdateCacheToCurrentChunk (Unity.Entities.ComponentChunkCache& cache, System.Boolean isWriting, System.Int32 indexInComponentGroup) (at <49b513de354643a2a0a32b80e091e5a5>:0)
Unity.Entities.ComponentChunkIterator.MoveToEntityIndexAndUpdateCache (System.Int32 index, Unity.Entities.ComponentChunkCache& cache, System.Boolean isWriting) (at <49b513de354643a2a0a32b80e091e5a5>:0)
Unity.Entities.EntityArray.get_Item (System.Int32 index) (at <49b513de354643a2a0a32b80e091e5a5>:0)
AttackSystem.OnUpdate () (at Assets/Scripts/ECS/Systems/Shooting/AttackSystem.cs:33)
Unity.Entities.ComponentSystem.InternalUpdate () (at <49b513de354643a2a0a32b80e091e5a5>:0)
Unity.Entities.ScriptBehaviourManager.Update () (at <49b513de354643a2a0a32b80e091e5a5>:0)
Unity.Entities.ScriptBehaviourUpdateOrder+DummyDelagateWrapper.TriggerUpdate () (at <49b513de354643a2a0a32b80e091e5a5>:0)


The entitiy debugger shows the correct Entity (14) in the attack system:

(side note: why does that 2nd component group get 3 'ammo' tags? I see this a lot.)

Here is the attack system code:

Code (CSharp):

1. using Unity.Entities;
2. using UnityEngine;
3.  
4. public struct AttackingTag : IComponentData { }
5.  
6. public class AttackSystem : ComponentSystem
7. {
8.     private ComponentGroup _nonAttackingGroup;
9.     private ComponentGroup _attackingGroup;
10.     private readonly AttackingTag _attacking = new AttackingTag();
11.  
12.     protected override void OnCreateManager()
13.     {
14.         _nonAttackingGroup = GetComponentGroup(new EntityArchetypeQuery()
15.         {
16.             All = new ComponentType[] { typeof(Ammo) },
17.             None = new ComponentType[] { typeof(AttackingTag) }
18.         });
19.  
20.         _attackingGroup = GetComponentGroup(typeof(Ammo), typeof(AttackingTag));
21.     }
22.  
23.     protected override void OnUpdate()
24.     {
25.         var nonAttackingEntities = _nonAttackingGroup.GetEntityArray();
26.  
27.         var mouseDown = Input.GetMouseButton(0);
28.         if (mouseDown)
29.         {
30.             for (var i = 0; i < nonAttackingEntities.Length; i++)
31.             {
32.                 // The Debug sometimes throws null reference exception, sometimes logs out an entity with a huge index number, sometimes logs the correct player entity (14) and works
33.                 Debug.Log(nonAttackingEntities[i]);
34.             }
35.         }
36.     }
37. }

This was working fine when I was using [Inject] but I've been trying to move away from that since it is being deprecated.

 

When you use the EntityManager to add or remove components you invalidate your arrays of entities. Use a command buffer instead and queue up your adds and removals. PostUpdateCommands is a command buffer that will playback your commands after the system has updated. So to fix your issue, use PostUpdateCommands.AddComponent and PostUpdateCommands.RemoveComponent instead of the EntityManager.

 

I have tried that too. It breaks before it even reaches that line. It breaks just reading at the Debug.Log(entities); line before I even do Add or Remove component. I tried PostUpdateCommands, BarrierSystems, and EntityManager and get the same strange intermittent issues. The thing that gets me is that it's intermittent. It works after a fresh recompile but doesn't work on every subsequent 'play'.

 

hmm, do you perhaps need to set the "Any" array in EntityArchetypeQuery to an empty array instead of null?

 

That doesn't seem to fix it either.

I've been doing some more reading and it looks like I might have to bite the bullet and go with chunk iteration.

 

Change

Code (CSharp):

1. _nonAttackingGroup = GetComponentGroup(new EntityArchetypeQuery()
2.         {
3.             All = new ComponentType[] { typeof(Ammo) },
4.             None = new ComponentType[] { typeof(AttackingTag) }
5.         });
6.  

To

Code (CSharp):

1. _nonAttackingGroup = GetComponentGroup(typeof(Ammo), ComponentType.SubtractiveComponent<AttackingTag>());
2.  

 

He's trying to move away from code that will be removed so I don't think you should be suggesting he changes back.

But yeah the issue is GetEntityArray() (and GetComponentDataArray()) does not work when you are passing an archetype query - you're meant to be doing chunk iteration.

 

I am fixing the issue. Nothing else. When they will introduce the new simillar API he will just change one line of code. And I didn't suggest anything that will be removed though. ComponentGroup won't be removed.