Proximity grid list reuse

src/DotRecast.Core/Buffers/RcObjectPool.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+
+namespace DotRecast.Core.Buffers
+{
+    // This implementation is thread unsafe
+    public class RcObjectPool<T> where T : class
+    {
+        private readonly Queue<T> _items = new Queue<T>();
+        private readonly Func<T> _createFunc;
+
+        public RcObjectPool(Func<T> createFunc)
+        {
+            _createFunc = createFunc;
+        }
+
+        public T Get()
+        {
+            if (_items.TryDequeue(out var result))
+                return result;
+
+            return _createFunc();
+        }
+
+        public void Return(T obj)
+        {
+            _items.Enqueue(obj);
+        }
+    }
+}

src/DotRecast.Detour.Crowd/DtCrowd.cs

@@ -129,7 +129,7 @@ namespace DotRecast.Detour.Crowd
         private readonly DtObstacleAvoidanceParams[] _obstacleQueryParams;
         private readonly DtObstacleAvoidanceQuery _obstacleQuery;
 
-        private DtProximityGrid _grid;
+        private readonly DtProximityGrid _grid;
 
         private int _maxPathResult;
         private readonly RcVec3f _agentPlacementHalfExtents;
@@ -174,6 +174,7 @@ namespace DotRecast.Detour.Crowd
             _agentIdx = new RcAtomicInteger(0);
             _agents = new Dictionary<int, DtCrowdAgent>();
             _activeAgents = new List<DtCrowdAgent>();
+            _grid = new DtProximityGrid(_config.maxAgentRadius * 3);
 
             // The navQuery is mostly used for local searches, no need for large node pool.
             SetNavMesh(nav);
@@ -864,7 +865,7 @@ namespace DotRecast.Detour.Crowd
         {
             using var timer = _telemetry.ScopedTimer(DtCrowdTimerLabel.BuildProximityGrid);
 
-            _grid = new DtProximityGrid(_config.maxAgentRadius * 3);
+            _grid.Clear();
 
             for (var i = 0; i < agents.Count; i++)
             {

src/DotRecast.Detour.Crowd/DtProximityGrid.cs

@@ -22,6 +22,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.CompilerServices;
+using DotRecast.Core.Buffers;
 
 namespace DotRecast.Detour.Crowd
 {
@@ -30,12 +31,14 @@ namespace DotRecast.Detour.Crowd
         private readonly float _cellSize;
         private readonly float _invCellSize;
         private readonly Dictionary<long, List<DtCrowdAgent>> _items;
+        private readonly RcObjectPool<List<DtCrowdAgent>> _listPool;
 
         public DtProximityGrid(float cellSize)
         {
             _cellSize = cellSize;
             _invCellSize = 1.0f / cellSize;
             _items = new Dictionary<long, List<DtCrowdAgent>>();
+            _listPool = new RcObjectPool<List<DtCrowdAgent>>(() => new List<DtCrowdAgent>());
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -57,6 +60,8 @@ namespace DotRecast.Detour.Crowd
 
         public void Clear()
         {
+            foreach (var pair in _items)
+                _listPool.Return(pair.Value);
             _items.Clear();
         }
 
@@ -74,7 +79,7 @@ namespace DotRecast.Detour.Crowd
                     long key = CombineKey(x, y);
                     if (!_items.TryGetValue(key, out var ids))
                     {
-                        ids = new List<DtCrowdAgent>();
+                        ids = _listPool.Get();
                         _items.Add(key, ids);
                     }