SystemBase ECS unity doesnt let me acess NativeMultiHashMap because it isnt readonly?

Question

     using System.Collections;
     using System.Collections.Generic;
     using UnityEngine;
     using Unity.Entities;
     using Unity.Transforms;
     using Unity.Mathematics;
     using Unity.Collections;
     using Unity.Rendering;
     using Unity.Burst;
     using Unity.Jobs;
     
     
     
     public struct QuadrantData {
         public Entity entity;
         public Soldier soldier;
     }
     
     public class QuadrantSystem : SystemBase {
     
         EntityQuery entityQuery;
     
         public static NativeMultiHashMap<int, QuadrantData> quadrantMultiHashMap;
     
         public const int quadrantYMultiplier = 1000;
         private const int quadrantCellSize = 3;
     
         public static int GetPositionHashMapKey(int2 position) {
             return ((position.x / quadrantCellSize) + (quadrantYMultiplier * (position.y / quadrantCellSize)));
         }
     
         private static void DebugDrawQuadrant(float3 position) {
             Vector3 lowerLeft = new Vector3(math.floor(position.x / quadrantCellSize) * quadrantCellSize,0, math.floor(position.z / quadrantCellSize) * quadrantCellSize);
             Debug.DrawLine(lowerLeft, lowerLeft + new Vector3(+1,0, +0) * quadrantCellSize);
             Debug.DrawLine(lowerLeft, lowerLeft + new Vector3(+0,0, +1) * quadrantCellSize);
             Debug.DrawLine(lowerLeft + new Vector3(+1,0, +0) * quadrantCellSize, lowerLeft + new Vector3(+1,0, +1) * quadrantCellSize);
             Debug.DrawLine(lowerLeft + new Vector3(+0,0, +1) * quadrantCellSize, lowerLeft + new Vector3(+1,0, +1) * quadrantCellSize);
             //Debug.Log(GetPositionHashMapKey(position) + " " + position);
         }
     
         private static int GetEntityCountInHashMap(NativeMultiHashMap<int, QuadrantData> quadrantMultiHashMap, int hashMapKey) {
             QuadrantData quadrantData;
             NativeMultiHashMapIterator<int> nativeMultiHashMapIterator;
             int count = 0;
             if (quadrantMultiHashMap.TryGetFirstValue(hashMapKey, out quadrantData, out nativeMultiHashMapIterator)) {
                 do {
                     count++;
                 } while (quadrantMultiHashMap.TryGetNextValue(out quadrantData, ref nativeMultiHashMapIterator));
             }
             return count;
         }
         protected override void OnCreate()
         {
             quadrantMultiHashMap = new NativeMultiHashMap<int, QuadrantData>(0, Allocator.Persistent);
             base.OnCreate();
         }
     
         protected override void OnDestroy() {
             quadrantMultiHashMap.Dispose();
             base.OnDestroy();
         }
     
         protected override void OnUpdate() {
     
             entityQuery = GetEntityQuery(typeof(Translation), typeof(Soldier));
             quadrantMultiHashMap.Clear();
             if (entityQuery.CalculateEntityCount() > quadrantMultiHashMap.Capacity) {
                 quadrantMultiHashMap.Capacity = entityQuery.CalculateEntityCount();
             }
     
             Entities.ForEach((Entity entity,in Soldier soldier) =>
             {
                 int hashMapKey = GetPositionHashMapKey(soldier.Index);
                 quadrantMultiHashMap.Add(hashMapKey, new QuadrantData
                 {
                     entity = entity,
                     soldier = soldier,
                 });
             }).WithStoreEntityQueryInField(ref entityQuery)
              .ScheduleParallel();
     
             this.CompleteDependency();
         }
     
     }

I recieve this error?

C:\Dev\ECS Massive Battle\Assets\Scripts\QuadrantSystem.cs(74,13): Burst error BC1042: The managed class type Unity.Collections.NativeMultiHashMap2*` is not supported. Loading from a non-readonly static field QuadrantSystem.quadrantMultiHashMap is not supported

Answer 1

Answer by andrew-lukasik · Jun 03, 2021 at 06:06 PM

It won't let you access it because you are referencing a managed field from inside a job. This is not allowed. Thankfully, solution to this is very simple - make a local alias variable for jobs to copy by value.

 var quadrants = quadrantMultiHashMap.AsParallelWriter();
 Entities
     .ForEach( ( Entity entity ,in Soldier soldier ) =>
     {
         int hashMapKey = GetPositionHashMapKey(soldier.Index);
         quadrants.Add( hashMapKey , new QuadrantData{ entity = entity, soldier = soldier, });
     } )
     .ScheduleParallel();

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critterawesome · Jun 03, 2021 at 06:53 PM 0

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Thanks for answering! I tried it but now it says that

InvalidOperationException: <>c__DisplayClass_OnUpdate_LambdaJob0.JobData.quadrants is not declared [ReadOnly] in a IJobParallelFor job. The container does not support parallel writing. Please use a more suitable container type.

andrew-lukasik critterawesome · Jun 03, 2021 at 07:19 PM 0

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Replace ScheduleParallel with Schedule (single thread)

OR use parallel writer:

 var quadrants = quadrantMultiHashMap.AsParallelWriter();

critterawesome andrew-lukasik · Jun 03, 2021 at 07:44 PM 0

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look at the answer below though am i supposed to access quadrants? I need a way for unity to read the static variable quadrantMultiHashMap without making it readonly as i can change the size without an error.

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critterawesome · Jun 03, 2021 at 07:42 PM 0

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Yeah but i've heard that multithread is faster

andrew-lukasik critterawesome · Jun 03, 2021 at 08:21 PM 0

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It often is, but it introduces thread-safety considerations

critterawesome · Jun 03, 2021 at 08:40 PM 0

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One question on how to use this method do i acess the var quadrants that you recomended instead of the quadrantMultiHashMap like i did below?

andrew-lukasik critterawesome · Jun 03, 2021 at 08:43 PM 0

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Use aliases when inside a job (and Entities.ForEach is one). You can access QuadrantSystem.quadrantMultiHashMap normally otherwise (given there is no dependency issues)

critterawesome · Jun 03, 2021 at 08:45 PM 0

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It works if i use withoutburst but i know this can limit my performance thricefold so could you give me an example of what my changed quadrantsystem should be?

andrew-lukasik critterawesome · Jun 03, 2021 at 08:54 PM 0

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Do you mean this code you posted in second answer? I.e.:

  int hashMapKey = QuadrantSystem.GetPositionHashMapKey(soldierComponent.Index - 1);
  QuadrantData quadrantData;
  NativeMultiHashMapIterator<int> nativeMultiHashMapIterator;
  if (QuadrantSystem.quadrantMultiHashMap.TryGetFirstValue(hashMapKey, out quadrantData, out nativeMultiHashMapIterator))
  {
      do
      {
          if (soldierComponent.id != quadrantData.soldier.id)
          {
              if (soldierComponent.Index.x - 1 == quadrantData.soldier.Index.x && soldierComponent.Index.y == quadrantData.soldier.Index.y)
              {
                  TargetIsBlocked = true;
              }
          }
      } while (QuadrantSystem.quadrantMultiHashMap.TryGetNextValue(out quadrantData, ref nativeMultiHashMapIterator) && !TargetIsBlocked);
  }

If yes - is it part of a job too?

critterawesome andrew-lukasik · Jun 03, 2021 at 08:55 PM 0

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no i meant the quadrant system class in the first one and yes the second system also inherits from systembase.

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Answer 2

Answer by critterawesome · Jun 03, 2021 at 06:58 PM

If it helps you i access the hashmap by doing this

 int hashMapKey = QuadrantSystem.GetPositionHashMapKey(soldierComponent.Index - 1);
 QuadrantData quadrantData;
 NativeMultiHashMapIterator<int> nativeMultiHashMapIterator;
 if (QuadrantSystem.quadrantMultiHashMap.TryGetFirstValue(hashMapKey, out quadrantData, out nativeMultiHashMapIterator))
 {
     do
     {
         if (soldierComponent.id != quadrantData.soldier.id)
         {
             if (soldierComponent.Index.x - 1 == quadrantData.soldier.Index.x && soldierComponent.Index.y == quadrantData.soldier.Index.y)
             {
                 TargetIsBlocked = true;
             }
         }
     } while (QuadrantSystem.quadrantMultiHashMap.TryGetNextValue(out quadrantData, ref nativeMultiHashMapIterator) && !TargetIsBlocked);
 }

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SystemBase ECS unity doesnt let me acess NativeMultiHashMap because it isnt readonly?

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