Question Memory access violation EntityCommandBuffer

We're experiencing some seemingly random crashes at the moment and I was wondering if somebody has any idea what it could be.

I've attached the error log and here is the corresponding burst compile method that is mentioned in the stacktrace:

Code (CSharp):

1. --method=Unity.Entities.EntityCommandBuffer, Unity.Entities, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null::_mono_to_burst_PlaybackChainChunk(System.IntPtr, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089|System.IntPtr, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089|Unity.Entities.EntityComponentStore+ArchetypeChanges&, Unity.Entities, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null|Unity.Entities.ECBSharedPlaybackState&, Unity.Entities, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null|System.IntPtr, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089|System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089|System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089|System.Boolean, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089|Unity.Entities.PlaybackPolicy, Unity.Entities, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null)--34146f210f5f72cb3338fe0fb7212d4f

Any potential ideas or ways we could further narrow this down are greatly appreciated.

 

This is nearly always caused by unsafe ECB operations. For example

ECB1.DestroyEntity(entity)
ECB2.[Add|Remove|Set]Component(entity)

ECB1 plays back, destroy entity
ECB2 plays back, entity doesn't exist, crashes

For safety I would suggest doing what I've dubbed, the Eizenhorn's approach - create a second EntityCommandBufferSystem dedicated to Destroy operations which runs after your EndSimulationEntityCommandBufferSystem and limit all destroy calls to this new command buffer. This way destroy should always be safe.

The one other fail that can happen is

ECB1.RemoveComponent(entity, ComponentA)
ECB2.SetComponent(entity, ComponentA)

ComponentA no longer exists so this is not safe. The fix is either structure your code in a way this can't happen or avoid using SetComponent and instead just always use AddComponent.

 

Thanks a lot for the answer, I'll look into it, this is definitely a starting point!