From 3e4b5b366077c5455f70d61aa466c27e27f57a37 Mon Sep 17 00:00:00 2001
From: vis2k <info@noobtuts.com>
Date: Sat, 17 Sep 2022 16:11:56 +0800
Subject: [PATCH] perf: Grid2D initial capacity to avoid warmup allocations

---
 .../SpatialHashing/Grid2D.cs                  | 36 +++++++++++--------
 .../SpatialHashingInterestManagement.cs       |  3 +-
 Assets/Mirror/Tests/Editor/Grid2DTests.cs     |  2 +-
 3 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/Assets/Mirror/Components/InterestManagement/SpatialHashing/Grid2D.cs b/Assets/Mirror/Components/InterestManagement/SpatialHashing/Grid2D.cs
index f4702ece5..41417cd04 100644
--- a/Assets/Mirror/Components/InterestManagement/SpatialHashing/Grid2D.cs
+++ b/Assets/Mirror/Components/InterestManagement/SpatialHashing/Grid2D.cs
@@ -18,22 +18,27 @@ public struct Grid2D<T>
         // => makes the code a lot easier too
         // => this is FINE because in the worst case, every grid position in the
         //    game world is filled with a player anyway!
-        readonly Dictionary<Vector2Int, HashSet<T>> grid =
-            new Dictionary<Vector2Int, HashSet<T>>();
+        readonly Dictionary<Vector2Int, HashSet<T>> grid;
 
         // cache a 9 neighbor grid of vector2 offsets so we can use them more easily
-        readonly Vector2Int[] neighbourOffsets =
+        readonly Vector2Int[] neighbourOffsets;
+
+        public Grid2D(int initialCapacity)
         {
-            Vector2Int.up,
-            Vector2Int.up + Vector2Int.left,
-            Vector2Int.up + Vector2Int.right,
-            Vector2Int.left,
-            Vector2Int.zero,
-            Vector2Int.right,
-            Vector2Int.down,
-            Vector2Int.down + Vector2Int.left,
-            Vector2Int.down + Vector2Int.right
-        };
+            grid = new Dictionary<Vector2Int, HashSet<T>>(initialCapacity);
+
+            neighbourOffsets = new[] {
+                Vector2Int.up,
+                Vector2Int.up + Vector2Int.left,
+                Vector2Int.up + Vector2Int.right,
+                Vector2Int.left,
+                Vector2Int.zero,
+                Vector2Int.right,
+                Vector2Int.down,
+                Vector2Int.down + Vector2Int.left,
+                Vector2Int.down + Vector2Int.right
+            };
+        }
 
         // helper function so we can add an entry without worrying
         public void Add(Vector2Int position, T value)
@@ -41,7 +46,10 @@ public void Add(Vector2Int position, T value)
             // initialize set in grid if it's not in there yet
             if (!grid.TryGetValue(position, out HashSet<T> hashSet))
             {
-                hashSet = new HashSet<T>();
+                // each grid entry may hold hundreds of entities.
+                // let's create the HashSet with a large initial capacity
+                // in order to avoid resizing & allocations.
+                hashSet = new HashSet<T>(128);
                 grid[position] = hashSet;
             }
 
diff --git a/Assets/Mirror/Components/InterestManagement/SpatialHashing/SpatialHashingInterestManagement.cs b/Assets/Mirror/Components/InterestManagement/SpatialHashing/SpatialHashingInterestManagement.cs
index 2f78e7254..298603497 100644
--- a/Assets/Mirror/Components/InterestManagement/SpatialHashing/SpatialHashingInterestManagement.cs
+++ b/Assets/Mirror/Components/InterestManagement/SpatialHashing/SpatialHashingInterestManagement.cs
@@ -40,7 +40,8 @@ public enum CheckMethod
         public bool showSlider;
 
         // the grid
-        Grid2D<NetworkConnectionToClient> grid = new Grid2D<NetworkConnectionToClient>();
+        // begin with a large capacity to avoid resizing & allocations.
+        Grid2D<NetworkConnectionToClient> grid = new Grid2D<NetworkConnectionToClient>(1024);
 
         // project 3d world position to grid position
         Vector2Int ProjectToGrid(Vector3 position) =>
diff --git a/Assets/Mirror/Tests/Editor/Grid2DTests.cs b/Assets/Mirror/Tests/Editor/Grid2DTests.cs
index 34c3b88b6..c445d1a38 100644
--- a/Assets/Mirror/Tests/Editor/Grid2DTests.cs
+++ b/Assets/Mirror/Tests/Editor/Grid2DTests.cs
@@ -11,7 +11,7 @@ public class Grid2DTests
         [SetUp]
         public void SetUp()
         {
-            grid = new Grid2D<int>();
+            grid = new Grid2D<int>(10);
         }
 
         [Test]