Rework entity storage to remove CullDeletedEntities.

Now we only use the dictionary for storing entities, similar to components.

This means creating/deleting entities while enumerating them will throw, but that's probably fine since GetEntities() is barely used nowadays, and we have QueueDelete().

Robust.Server/GameObjects/ServerEntityManager.cs

@@ -127,7 +127,7 @@ namespace Robust.Server.GameObjects
 
             base.TickUpdate(frameTime, histogram);
 
-            EntitiesCount.Set(AllEntities.Count);
+            EntitiesCount.Set(Entities.Count);
         }
 
         public uint GetLastMessageSequence(IPlayerSession session)

Robust.Shared/GameObjects/EntityManager.cs

@@ -48,8 +48,6 @@ namespace Robust.Shared.GameObjects
         /// </summary>
         protected readonly Dictionary<EntityUid, Entity> Entities = new();
 
-        protected readonly List<Entity> AllEntities = new();
-
         private EntityEventBus _eventBus = null!;
 
         protected virtual int NextEntityUid { get; set; } = (int)EntityUid.FirstUid;
@@ -124,11 +122,6 @@ namespace Robust.Shared.GameObjects
             {
                 _componentManager.CullRemovedComponents();
             }
-
-            using (histogram?.WithLabels("EntityCull").NewTimer())
-            {
-                CullDeletedEntities();
-            }
         }
 
         public virtual void FrameUpdate(float frameTime)
@@ -225,21 +218,7 @@ namespace Robust.Shared.GameObjects
         }
 
         /// <inheritdoc />
-        public IEnumerable<IEntity> GetEntities()
-        {
-            // Need to do an iterator loop to avoid issues with concurrent access.
-            // ReSharper disable once ForCanBeConvertedToForeach
-            for (var i = 0; i < AllEntities.Count; i++)
-            {
-                var entity = AllEntities[i];
-                if (entity.Deleted)
-                {
-                    continue;
-                }
-
-                yield return entity;
-            }
-        }
+        public IEnumerable<IEntity> GetEntities() => Entities.Values;
 
         /// <summary>
         /// Shuts-down and removes given Entity. This is also broadcast to all clients.
@@ -293,6 +272,7 @@ namespace Robust.Shared.GameObjects
             entity.LifeStage = EntityLifeStage.Deleted;
             EntityDeleted?.Invoke(this, entity.Uid);
             EventBus.RaiseEvent(EventSource.Local, new EntityDeletedMessage(entity));
+            Entities.Remove(entity.Uid);
         }
 
         public void QueueDeleteEntity(IEntity entity)
@@ -333,8 +313,6 @@ namespace Robust.Shared.GameObjects
             {
                 DeleteEntity(e);
             }
-
-            CullDeletedEntities();
         }
 
         /// <summary>
@@ -379,7 +357,6 @@ namespace Robust.Shared.GameObjects
 
             // We do this after the event, so if the event throws we have not committed
             Entities[entity.Uid] = entity;
-            AllEntities.Add(entity);
 
             // allocate the required MetaDataComponent
             _componentManager.AddComponent<MetaDataComponent>(entity);
@@ -445,27 +422,6 @@ namespace Robust.Shared.GameObjects
             EntityStarted?.Invoke(this, entity.Uid);
         }
 
-        private void CullDeletedEntities()
-        {
-            // Culling happens in updates.
-            // It doesn't matter because to-be culled entities can't be accessed.
-            // This should prevent most cases of "somebody is iterating while we're removing things"
-            for (var i = 0; i < AllEntities.Count; i++)
-            {
-                var entity = AllEntities[i];
-                if (!entity.Deleted)
-                {
-                    continue;
-                }
-
-                AllEntities.RemoveSwap(i);
-                Entities.Remove(entity.Uid);
-
-                // Process the one we just swapped next.
-                i--;
-            }
-        }
-
 #endregion Entity Management
 
         protected void DispatchComponentMessage(NetworkComponentMessage netMsg)