DOTS - ECS Worlds entity transfer error (Halp!)

Question

Hello, I am making a loading system for my project and one part of it has to do with transporting entities between worlds. It works correctly, but i get this error: ArgumentException: System.InvalidOperationException: The entity does not exist Thrown from job: Unity.Entities.EntityCommandBuffer._mono_to_burst_PlaybackChainChunk

Also, trough testing I found out the error is specifically in the tranfer of entities between worlds, in my main script (bellow).

The entire code message: ArgumentException: System.InvalidOperationException: The entity does not exist Thrown from job: Unity.Entities.EntityCommandBuffer._mono_to_burst_PlaybackChainChunk This Exception was thrown from a function compiled with Burst, which has limited exception support. Turn off burst (Jobs -> Burst -> Enable Compilation) to inspect full exceptions & stacktraces. EntityCommandBuffer was recorded in WorldLoader and played back in Unity.Entities.EndSimulationEntityCommandBufferSystem. at (wrapper managed-to-native) System.Object.wrapper_native_000001DB2D3901E0(intptr,intptr,Unity.Entities.EntityComponentStore/ArchetypeChanges&,Unity.Entities.ECBSharedPlaybackState&,intptr,int,int,bool,Unity.Entities.PlaybackPolicy) at (wrapper delegate-invoke) .invoke_void_intptr_intptr_EntityComponentStore/ArchetypeChanges&_ECBSharedPlaybackState&_intptr_int_int_bool_PlaybackPolicy(intptr,intptr,Unity.Entities.EntityComponentStore/ArchetypeChanges&,Unity.Entities.ECBSharedPlaybackState&,intptr,int,int,bool,Unity.Entities.PlaybackPolicy) at Unity.Entities.EntityCommandBuffer._forward_mono_PlaybackChainChunk (Unity.Entities.EntityDataAccess mgr, Unity.Collections.LowLevel.Unsafe.UnsafeList* managedReferenceIndexRemovalCount, Unity.Entities.EntityComponentStore+ArchetypeChanges& archetypeChanges, Unity.Entities.ECBSharedPlaybackState& playbackState, Unity.Entities.ECBChainPlaybackState* chainStates, System.Int32 currentChain, System.Int32 nextChain, System.Boolean isFirstPlayback, Unity.Entities.PlaybackPolicy playbackPolicy) [0x00000] in C:\Users\Tom\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.interop.gen.cs:88 at Unity.Entities.EntityCommandBuffer.PlaybackChainChunk (Unity.Entities.EntityDataAccess* mgr, Unity.Collections.LowLevel.Unsafe.UnsafeList* managedReferenceIndexRemovalCount, Unity.Entities.EntityComponentStore+ArchetypeChanges& archetypeChanges, Unity.Entities.ECBSharedPlaybackState& playbackState, Unity.Entities.ECBChainPlaybackState* chainStates, System.Int32 currentChain, System.Int32 nextChain, System.Boolean isFirstPlayback, Unity.Entities.PlaybackPolicy playbackPolicy) [0x00007] in C:\Users\Tom\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.interop.gen.cs:69 at Unity.Entities.EntityCommandBuffer.PlaybackChain (Unity.Entities.EntityDataAccess* mgr, Unity.Collections.LowLevel.Unsafe.UnsafeList* managedReferenceIndexRemovalCount, Unity.Entities.EntityComponentStore+ArchetypeChanges& archetypeChanges, Unity.Entities.ECBSharedPlaybackState& playbackState, Unity.Entities.ECBChainPlaybackState* chainStates, System.Int32 currentChain, System.Int32 nextChain, System.Boolean isFirstPlayback, Unity.Entities.PlaybackPolicy playbackPolicy) [0x000b2] in C:\Users\Tom\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.cs:1678 at Unity.Entities.EntityCommandBuffer.PlaybackInternal (Unity.Entities.EntityDataAccess* mgr) [0x0030f] in C:\Users\Tom\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.cs:1502 at Unity.Entities.EntityCommandBuffer.Playback (Unity.Entities.EntityManager mgr) [0x00000] in C:\Users\Tom\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.cs:1369 at Unity.Entities.EntityCommandBufferSystem.FlushPendingBuffers (System.Boolean playBack) [0x0007f] in C:\Users\Tom\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBufferSystem.cs:225

Unity.Entities.EntityCommandBufferSystem.FlushPendingBuffers (System.Boolean playBack) (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/EntityCommandBufferSystem.cs:292) Unity.Entities.EntityCommandBufferSystem.OnUpdate () (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/EntityCommandBufferSystem.cs:190) Unity.Entities.ComponentSystem.Update () (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystem.cs:113) Unity.Entities.ComponentSystemGroup.UpdateAllSystems () (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystemGroup.cs:435) UnityEngine.Debug:LogException(Exception) Unity.Debug:LogException(Exception) (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/Stubs/Unity/Debug.cs:19) Unity.Entities.ComponentSystemGroup:UpdateAllSystems() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystemGroup.cs:440) Unity.Entities.ComponentSystemGroup:OnUpdate() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystemGroup.cs:387) Unity.Entities.ComponentSystem:Update() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystem.cs:113) Unity.Entities.DummyDelegateWrapper:TriggerUpdate() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ScriptBehaviourUpdateOrder.cs:333)

Can anyone explain to me why it happens and how to fix it, please. Anyway here is my entire code (happy reading trough it :D):

My main code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Unity.Collections;
 using System.IO;
 using Unity.Mathematics;
 using Unity.Transforms;
 using Unity.Entities;
 using Unity.Entities.Serialization;
 using Unity.Jobs;
 using Unity.Burst;
 using static WorldUtils;
 using static WorldData;
 using static ArchetypeLibrary;
 
 public class WorldLoader : SystemBase
 {
     EndSimulationEntityCommandBufferSystem ECBS;
 
     NativeHashSet<int2> ActiveChunks;
     NativeHashSet<int2> LoadedChunks;
     NativeHashSet<int2> PendingChunks;
 
     EntityQuery Query;
 
     protected override void OnCreate()
     {
         ECBS = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
 
         ActiveChunks = new NativeHashSet<int2>(1600, Allocator.Persistent);
         LoadedChunks = new NativeHashSet<int2>(1600, Allocator.Persistent);
         PendingChunks = new NativeHashSet<int2>(1600, Allocator.Persistent);
         Query = GetEntityQuery(typeof(PendingSave));
     }
 
     protected override void OnUpdate()
     {
         ActiveChunks.Clear();
 
         var activeChunks = ActiveChunks;
         var loadedChunks = LoadedChunks;
         var pendingChunks = PendingChunks;
 
         var chunkSize = ChunkSize;
         var chunkArchetype = ChunkArchetype();
         var worldSeed = WorldSeed;
 
         var ECB = ECBS.CreateCommandBuffer();
         var PECB = ECB.AsParallelWriter();
 
         var saveWorld = FindWorld("SaveWorld");
 
         //Activate chunks around Loaders
         Entities.ForEach((in Translation translation, in Loader loader) =>
         {
             float2 Position = new float2(translation.Value.x, translation.Value.y);
             int LoadDistance = loader.LoadDistance;
 
             for (int x = 0; x < LoadDistance; x++)
             {
                 for (int y = 0; y < LoadDistance; y++)
                 {
                     int2 chunk = GetChunkFromWorld(Position, chunkSize, new float2(0, 0)) - LoadDistance / 2 + new int2(x, y);
                     if (!activeChunks.Contains(chunk))
                     {
                         activeChunks.Add(chunk);
                     }
                 }
             }
         }).WithBurst().Schedule();
 
         //Load and unload chunks and keep track of newly generated
         Job.WithReadOnly(activeChunks).WithCode(() =>
         {
             var activeChunksArray = activeChunks.ToNativeArray(Allocator.Temp);
             for (int i = 0; i < activeChunksArray.Length; i++)
             {
                 int2 chunk = activeChunksArray[i];
                 if (!loadedChunks.Contains(chunk))
                 {
                     loadedChunks.Add(chunk);
                     pendingChunks.Add(chunk);
                 }
             }
             var loadedChunksArray = loadedChunks.ToNativeArray(Allocator.Temp);
             for (int i = loadedChunksArray.Length - 1; i != -1; i--)
             {
                 int2 chunk = loadedChunksArray[i];
 
                 if (!activeChunks.Contains(chunk))
                 {
                     loadedChunks.Remove(chunk);
                 }
             }
         }).WithBurst().Schedule();
 
         //Generate new chunks
         Job.WithCode(() =>
         {
             var pendingChunksArray = pendingChunks.ToNativeArray(Allocator.Temp);
             for (int i = pendingChunksArray.Length - 1; i != -1; i--)
             {
                 int2 chunk = pendingChunksArray[i];
 
                 Entity entity = ECB.CreateEntity(chunkArchetype);
                 float2 position = GetTileCenter(GetWorldFromChunk(chunk, chunkSize, new float2(0, 0)), chunkSize);
 
                 ECB.SetComponent(entity, new Translation { Value = new float3(position.x, position.y, 0) });
                 ECB.SetComponent(entity, new Unloadable { Serializable = true });
                 ECB.SetComponent(entity, new ChunkData { NewChunk = true, ChunkTick = true, WorldSeed = worldSeed });
                 ECB.AddBuffer<TileData>(entity);
 
                 pendingChunks.Remove(chunk);
             }
         }).WithBurst().Schedule();
 
         //Destroy unloaded entities or select them for serialization
         Entities.WithReadOnly(loadedChunks).ForEach((int entityInQueryIndex, Entity entity, ref Unloadable unloadable, in Translation translation) =>
         {
             int2 chunk = GetChunkFromWorld(new float2(translation.Value.x, translation.Value.y), chunkSize, new float2(0, 0));
 
             if (!loadedChunks.Contains(chunk))
             {
                 if (unloadable.Serializable == true)
                 {
                     PECB.AddComponent(entityInQueryIndex, entity, new PendingSave { });
                 }
                 else
                 {
                     PECB.DestroyEntity(entityInQueryIndex, entity);
                 }
             }
         }).WithBurst().ScheduleParallel();
         
         ECBS.AddJobHandleForProducer(Dependency);
         Dependency.Complete();
         
         //Move selected entities to SaveWorld
         if (Query.IsEmpty == false)
         {
             saveWorld.EntityManager.MoveEntitiesFrom(World.EntityManager, Query);
         }
     }
 
     protected override void OnDestroy()
     {
         ActiveChunks.Dispose();
         LoadedChunks.Dispose();
         PendingChunks.Dispose();
     }
 }

My main code library:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Unity.Collections;
 using Unity.Mathematics;
 using Unity.Transforms;
 using Unity.Entities;
 using Unity.Jobs;
 using Unity.Burst;
 
 public static class WorldUtils
 {
     public static int2 GetTileFromWorld(float2 WorldPosition, float2 OriginPosition, float TileSize)
     {
         int2 TilePosition;
         TilePosition.x = (int)math.floor((WorldPosition - OriginPosition).x / TileSize);
         TilePosition.y = (int)math.floor((WorldPosition - OriginPosition).y / TileSize);
         return TilePosition;
     }
 
     public static float2 GetWorldFromTile(int2 TilePosition, float TileSize, float2 OriginPosition)
     {
         float2 WorldPosition;
         WorldPosition.x = (TilePosition.x * TileSize) + OriginPosition.x;
         WorldPosition.y = (TilePosition.y * TileSize) + OriginPosition.y;
         return WorldPosition;
     }
 
     public static float2 GetTileCenter(float2 WorldPosition, float TileSize)
     {
         return new float2((WorldPosition.x + (TileSize * 0.5f)), (WorldPosition.y + (TileSize * 0.5f)));
     }
 
     public static int2 GetChunkFromWorld(float2 WorldPosition, int ChunkSize, float2 OriginPosition)
     {
         int2 ChunkPosition;
         ChunkPosition.x = (int)(math.floor((WorldPosition.x - OriginPosition.x) / ChunkSize));
         ChunkPosition.y = (int)(math.floor((WorldPosition.y - OriginPosition.y) / ChunkSize));
         return ChunkPosition;
     }
 
     public static float2 GetWorldFromChunk(int2 ChunkPosition, int ChunkSize, float2 OriginPosition)
     {
         float2 WorldPosition;
         WorldPosition.x = (ChunkPosition.x * ChunkSize) + OriginPosition.x;
         WorldPosition.y = (ChunkPosition.y * ChunkSize) + OriginPosition.y;
         return WorldPosition;
     }
 
     public static float PerlinSeeder(float WorldSeed)
     {
         float Result = math.cos(WorldSeed);
         return Result;
     }
 
     public static World FindWorld(string name)
     {
         var worlds = World.All;
         for (int i = 0; i < worlds.Count; i++)
             if (worlds[i].Name == name) return worlds[i];
         return null;
     }
 }

And finally my monobehavior script that tests the other codes:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Unity.Collections;
 using Unity.Mathematics;
 using Unity.Transforms;
 using Unity.Entities;
 using Unity.Jobs;
 using Unity.Burst;
 using static WorldUtils;
 using static WorldData;
 using static ArchetypeLibrary;
 
 public class Test : MonoBehaviour
 {
     public float2 Position;
     EntityManager EntityManager;
     Entity entity;
 
     public float t;
     public bool End;
     public int EndTime;
     public float worldSeed;
     public World worldname;
 
 
     private void Start()
     {
         EntityManager = World.DefaultGameObjectInjectionWorld.EntityManager;
         WorldSeed = worldSeed;
         var world = new World("SaveWorld");
     }
 
     private void Update()
     {
         t += 1 * Time.deltaTime;
 
 
         if (Input.GetKeyDown(KeyCode.G))
         {
             t = 0;
             entity = EntityManager.CreateEntity(typeof (Translation), typeof (Loader));
             EntityManager.SetComponentData(entity, new Translation { Value = new float3(Position.x, Position.y, 0) });
             EntityManager.SetComponentData(entity, new Loader { LoadDistance = 40 });
         }
 
         if (End == true && t >= EndTime)
         {
             EntityManager.DestroyEntity(entity);
             t = 0;
         }
     }
 }

Answer 1

Best Answer

Answer by andrew-lukasik · Dec 26, 2020 at 04:42 PM

 ECBS.AddJobHandleForProducer( Dependency );
 Dependency.Complete();

Calling Dependency.Complete(); creates pool of commands without executing them yet. So, you're seeing this error precisely because commands are ready and scheduled for old entities with EndSimulationEntityCommandBufferSystem meanwhile you destroy/move them, before valid buffered commands have any chance of being executed yet, by calling

 saveWorld.EntityManager.MoveEntitiesFrom(World.EntityManager, Query);

To fix this, don't schedule commands with EndSimulationEntityCommandBufferSystem here but just execute them immediately

 // ECBS.AddJobHandleForProducer( Dependency );// remove this line
 Dependency.Complete();
 ECB.Playback( EntityManager );

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andrew-lukasik · Dec 26, 2020 at 04:57 PM 0

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Or, in other words, replace:

 ECBS.AddJobHandleForProducer(Dependency);
 Dependency.Complete();
 
 //$$anonymous$$ove selected entities to SaveWorld
 if (Query.IsEmpty == false)
 {
     saveWorld.Entity$$anonymous$$anager.$$anonymous$$oveEntitiesFrom(World.Entity$$anonymous$$anager, Query);
 }

with:

 //$$anonymous$$ove selected entities to SaveWorld
 if( Query.IsEmpty==false )
 {
     Dependency.Complete();
     ECB.Playback( Entity$$anonymous$$anager );
     saveWorld.Entity$$anonymous$$anager.$$anonymous$$oveEntitiesFrom(World.Entity$$anonymous$$anager, Query);
 }
 else
 {
     // no need for Dependency.Complete() here
     ECBS.AddJobHandleForProducer(Dependency);
 }

Klusimo · Dec 27, 2020 at 11:03 AM 0

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Thanks, that worked, but now I get this error instead:

ArgumentException: Attempt to call Playback() on an EntityCommandBuffer that has already been played back. EntityCommandBuffers created with the SinglePlayback policy can only be played back once. EntityCommandBuffer was recorded in WorldLoader and played back in Unity.Entities.EndSimulationEntityCommandBufferSystem. at Unity.Entities.EntityCommandBuffer.PlaybackInternal (Unity.Entities.EntityDataAccess mgr) [0x004ba] in C:\Users\$$anonymous$$\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.cs:1545 at Unity.Entities.EntityCommandBuffer.Playback (Unity.Entities.Entity$$anonymous$$anager mgr) [0x00000] in C:\Users\$$anonymous$$\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBuffer.cs:1369 at Unity.Entities.EntityCommandBufferSystem.FlushPendingBuffers (System.Boolean playBack) [0x0007f] in C:\Users\$$anonymous$$\Desktop\Unity\Projects\Qilligon\Library\PackageCache\com.unity.entities@0.16.0-preview.21\Unity.Entities\EntityCommandBufferSystem.cs:225 Unity.Entities.EntityCommandBufferSystem.FlushPendingBuffers (System.Boolean playBack) (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/EntityCommandBufferSystem.cs:292) Unity.Entities.EntityCommandBufferSystem.OnUpdate () (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/EntityCommandBufferSystem.cs:190) Unity.Entities.ComponentSystem.Update () (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystem.cs:113) Unity.Entities.ComponentSystemGroup.UpdateAllSystems () (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystemGroup.cs:435) UnityEngine.Debug:LogException(Exception) Unity.Debug:LogException(Exception) (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/Stubs/Unity/Debug.cs:19) Unity.Entities.ComponentSystemGroup:UpdateAllSystems() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystemGroup.cs:440) Unity.Entities.ComponentSystemGroup:OnUpdate() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystemGroup.cs:387) Unity.Entities.ComponentSystem:Update() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ComponentSystem.cs:113) Unity.Entities.DummyDelegateWrapper:TriggerUpdate() (at Library/PackageCache/com.unity.entities@0.16.0-preview.21/Unity.Entities/ScriptBehaviourUpdateOrder.cs:333)*

andrew-lukasik Klusimo · Dec 27, 2020 at 11:59 AM 0

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EntityCommandBuffer was recorded in WorldLoader and played back in Unity.Entities.EndSimulationEntityCommandBufferSystem.

As I wrote in code sample from comment above: either execute commands immediately ( ECB.Playback( Entity$$anonymous$$anager );) or schedule them for execution ( ECBS.AddJobHandleForProducer(Dependency);); never do both for the same command buffer as it would result in the same commands being executed twice (exception prevents that).

I.e. sequence like this is causing this exception:

 ECBS.AddJobHandleForProducer(Dependency);
 ECB.Playback( Entity$$anonymous$$anager );

(order doesn't matter, but both being called in single update do)

andrew-lukasik · Dec 27, 2020 at 12:13 PM 0

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Another alternative I would like to recommend is to reorder your OnUpdate from this:

 protected override void OnUpdate ()
 {
     /*
         all jobs being scheduled
     */
 
     ECBS.AddJobHandleForProducer(Dependency);
     Dependency.Complete();
     
     //$$anonymous$$ove selected entities to SaveWorld
     if( Query.IsEmpty==false )
     {
         saveWorld.Entity$$anonymous$$anager.$$anonymous$$oveEntitiesFrom(World.Entity$$anonymous$$anager, Query);
     }
 }

To this:

 protected override void OnUpdate ()
 {
     //$$anonymous$$ove selected entities to SaveWorld
     if( Query.IsEmpty==false )
     {
         Dependency.Complete();
         saveWorld.Entity$$anonymous$$anager.$$anonymous$$oveEntitiesFrom(World.Entity$$anonymous$$anager, Query);
     }
 
     /*
         all jobs being scheduled
     */
 
     ECBS.AddJobHandleForProducer(Dependency);
     // Dependency.Complete();// no need for that here
 }

So $$anonymous$$oveEntitiesFrom will interfere with command buffer no more.

Klusimo andrew-lukasik · Dec 27, 2020 at 05:12 PM 0

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Thanks so much, you once again saved me. I feel bad that you have to babysit me trought this entire code. I feel like you created it and I just stole it xD. Anyway thanks so much, I think there is good chance we´ll talk again soon :D

andrew-lukasik Klusimo · Dec 27, 2020 at 06:21 PM 0

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Happy to help. Don't worry, switching from $$anonymous$$onobehaviours to Dots is quite a leap and nobody is expected to make it effortlessly. Especially when learning/reference resources are both scarce and confusing due to being out of date much of the time.

DOTS - ECS Worlds entity transfer error (Halp!)

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