Fixed pooling of layers used for pathfinding.

The previous implementation:
- Was failing to dispose of pooled layers.
- Was using a finalizer to allow undisposed layers to be reused.

This means all pooled layers are kept alive indefinitely until the map changes. If the finalizer is slow for any reason then the pathfiinder will allocate new layers when the pool runs out. Since these new layers are eventually stuffed back into the pool when the finalizer does run, this can theoretically leak unbounded memory until the pool goes out of scope. In practice it would leak tens of megabytes.

The new implementation ensures layers are disposed and pooled correctly to allow proper memory reuse. It also introduces some safeguards against memory leaks:
- A cap is set on the number of pooled layers. If more concurrent layers are needed than this, then the excess layers will not be pooled but instead be allowed to be garbage collected.
- No finalizer. An implementation that fails to call dispose simply allows the layer to be garbage collected instead.

OpenRA.Mods.Common/Activities/FindResources.cs

@@ -123,8 +123,10 @@ namespace OpenRA.Mods.Common.Activities
 			var searchRadius = harv.LastOrderLocation.HasValue ? harvInfo.SearchFromOrderRadius : harvInfo.SearchFromProcRadius;
 			var searchRadiusSquared = searchRadius * searchRadius;
 
+			// Find any harvestable resources:
 			var passable = (uint)mobileInfo.GetMovementClass(self.World.TileSet);
-			var search = PathSearch.Search(self.World, mobileInfo, self, true,
+			List<CPos> path;
+			using (var search = PathSearch.Search(self.World, mobileInfo, self, true,
 				loc => domainIndex.IsPassable(self.Location, loc, passable) && self.CanHarvestAt(loc, resLayer, harvInfo, territory))
 				.WithCustomCost(loc =>
 				{
@@ -135,10 +137,8 @@ namespace OpenRA.Mods.Common.Activities
 					return 0;
 				})
 				.FromPoint(self.Location)
-				.FromPoint(searchFromLoc);
-
-			// Find any harvestable resources:
-			var path = pathFinder.FindPath(search);
+				.FromPoint(searchFromLoc))
+				path = pathFinder.FindPath(search);
 
 			if (path.Count > 0)
 				return path[0];

OpenRA.Mods.Common/Activities/Move/Move.cs

@@ -46,9 +46,14 @@ namespace OpenRA.Mods.Common.Activities
 			moveDisablers = self.TraitsImplementing<IDisableMove>().ToArray();
 
 			getPath = () =>
-				self.World.WorldActor.Trait<IPathFinder>().FindPath(
+			{
+				List<CPos> path;
+				using (var search =
 					PathSearch.FromPoint(self.World, mobile.Info, self, mobile.ToCell, destination, false)
-					.WithoutLaneBias());
+					.WithoutLaneBias())
+					path = self.World.WorldActor.Trait<IPathFinder>().FindPath(search);
+				return path;
+			};
 			this.destination = destination;
 			this.nearEnough = WDist.Zero;
 		}
@@ -85,9 +90,14 @@ namespace OpenRA.Mods.Common.Activities
 			moveDisablers = self.TraitsImplementing<IDisableMove>().ToArray();
 
 			getPath = () =>
-				self.World.WorldActor.Trait<IPathFinder>().FindPath(
+			{
+				List<CPos> path;
+				using (var search =
 					PathSearch.FromPoint(self.World, mobile.Info, self, mobile.ToCell, destination, false)
-					.WithIgnoredActor(ignoredActor));
+					.WithIgnoredActor(ignoredActor))
+					path = self.World.WorldActor.Trait<IPathFinder>().FindPath(search);
+				return path;
+			};
 
 			this.destination = destination;
 			this.nearEnough = WDist.Zero;

OpenRA.Mods.Common/Activities/Move/MoveAdjacentTo.cs

@@ -148,9 +148,8 @@ namespace OpenRA.Mods.Common.Activities
 			if (!searchCells.Any())
 				return NoPath;
 
-			var fromSrc = PathSearch.FromPoints(self.World, mobile.Info, self, searchCells, loc, true);
-			var fromDest = PathSearch.FromPoint(self.World, mobile.Info, self, loc, targetPosition, true).Reverse();
-
+			using (var fromSrc = PathSearch.FromPoints(self.World, mobile.Info, self, searchCells, loc, true))
+			using (var fromDest = PathSearch.FromPoint(self.World, mobile.Info, self, loc, targetPosition, true).Reverse())
 				return pathFinder.FindBidiPath(fromSrc, fromDest);
 		}
 

OpenRA.Mods.Common/OpenRA.Mods.Common.csproj

@@ -503,7 +503,7 @@
     <Compile Include="Traits\World\PaletteFromFile.cs" />
     <Compile Include="Traits\World\PaletteFromRGBA.cs" />
     <Compile Include="Traits\World\VoxelNormalsPalette.cs" />
-    <Compile Include="Pathfinder\CellInfoLayerManager.cs" />
+    <Compile Include="Pathfinder\CellInfoLayerPool.cs" />
     <Compile Include="Pathfinder\Constants.cs" />
     <Compile Include="Pathfinder\PathGraph.cs" />
     <Compile Include="Pathfinder\PathFinderUnitPathCacheDecorator.cs" />

OpenRA.Mods.Common/Pathfinder/BasePathSearch.cs

@@ -11,12 +11,11 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
-using OpenRA.Mods.Common.Traits;
 using OpenRA.Primitives;
 
 namespace OpenRA.Mods.Common.Pathfinder
 {
-	public interface IPathSearch
+	public interface IPathSearch : IDisposable
 	{
 		/// <summary>
 		/// The Graph used by the A*
@@ -163,5 +162,17 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public bool CanExpand { get { return !OpenQueue.Empty; } }
 		public abstract CPos Expand();
+
+		protected virtual void Dispose(bool disposing)
+		{
+			if (disposing)
+				Graph.Dispose();
+		}
+
+		public void Dispose()
+		{
+			Dispose(true);
+			GC.SuppressFinalize(this);
+		}
 	}
 }

OpenRA.Mods.Common/Pathfinder/CellInfoLayerManager.cs

@@ -1,111 +0,0 @@
-#region Copyright & License Information
-/*
- * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
- * This file is part of OpenRA, which is free software. It is made
- * available to you under the terms of the GNU General Public License
- * as published by the Free Software Foundation. For more information,
- * see COPYING.
- */
-#endregion
-
-using System.Collections.Generic;
-using System.Drawing;
-using OpenRA.Mods.Common.Traits;
-
-namespace OpenRA.Mods.Common.Pathfinder
-{
-	public interface ICellInfoLayerManager
-	{
-		/// <summary>
-		/// Gets a CellLayer of Nodes from the pool
-		/// </summary>
-		CellLayer<CellInfo> GetFromPool();
-
-		/// <summary>
-		/// Puts a CellLayer into the pool
-		/// </summary>
-		void PutBackIntoPool(CellLayer<CellInfo> ci);
-
-		/// <summary>
-		/// Creates (or obtains from the pool) a CellLayer given a map
-		/// </summary>
-		CellLayer<CellInfo> NewLayer(Map map);
-	}
-
-	public sealed class CellInfoLayerManager : ICellInfoLayerManager
-	{
-		readonly Queue<CellLayer<CellInfo>> cellInfoPool = new Queue<CellLayer<CellInfo>>();
-		readonly object defaultCellInfoLayerSync = new object();
-		CellLayer<CellInfo> defaultCellInfoLayer;
-
-		static ICellInfoLayerManager instance = new CellInfoLayerManager();
-
-		public static ICellInfoLayerManager Instance
-		{
-			get
-			{
-				return instance;
-			}
-		}
-
-		public static void SetInstance(ICellInfoLayerManager cellInfoLayerManager)
-		{
-			instance = cellInfoLayerManager;
-		}
-
-		public CellLayer<CellInfo> GetFromPool()
-		{
-			lock (cellInfoPool)
-				return cellInfoPool.Dequeue();
-		}
-
-		public void PutBackIntoPool(CellLayer<CellInfo> ci)
-		{
-			lock (cellInfoPool)
-				cellInfoPool.Enqueue(ci);
-		}
-
-		public CellLayer<CellInfo> NewLayer(Map map)
-		{
-			CellLayer<CellInfo> result = null;
-			var mapSize = new Size(map.MapSize.X, map.MapSize.Y);
-
-			// HACK: Uses a static cache so that double-ended searches (which have two PathSearch instances)
-			// can implicitly share data.  The PathFinder should allocate the CellInfo array and pass it
-			// explicitly to the things that need to share it.
-			while (cellInfoPool.Count > 0)
-			{
-				var cellInfo = GetFromPool();
-				if (cellInfo.Size != mapSize || cellInfo.Shape != map.TileShape)
-				{
-					Log.Write("debug", "Discarding old pooled CellInfo of wrong size.");
-					continue;
-				}
-
-				result = cellInfo;
-				break;
-			}
-
-			if (result == null)
-				result = new CellLayer<CellInfo>(map);
-
-			lock (defaultCellInfoLayerSync)
-			{
-				if (defaultCellInfoLayer == null ||
-				    defaultCellInfoLayer.Size != mapSize ||
-				    defaultCellInfoLayer.Shape != map.TileShape)
-				{
-					defaultCellInfoLayer =
-						CellLayer<CellInfo>.CreateInstance(
-							mpos => new CellInfo(int.MaxValue, int.MaxValue, mpos.ToCPos(map), CellStatus.Unvisited),
-							new Size(map.MapSize.X, map.MapSize.Y),
-							map.TileShape);
-				}
-
-				result.CopyValuesFrom(defaultCellInfoLayer);
-			}
-
-			return result;
-		}
-	}
-}

OpenRA.Mods.Common/Pathfinder/CellInfoLayerPool.cs

@@ -0,0 +1,78 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Drawing;
+
+namespace OpenRA.Mods.Common.Pathfinder
+{
+	sealed class CellInfoLayerPool
+	{
+		const int MaxPoolSize = 4;
+		readonly Stack<CellLayer<CellInfo>> pool = new Stack<CellLayer<CellInfo>>(MaxPoolSize);
+		readonly CellLayer<CellInfo> defaultLayer;
+
+		public CellInfoLayerPool(Map map)
+		{
+			defaultLayer =
+				CellLayer<CellInfo>.CreateInstance(
+					mpos => new CellInfo(int.MaxValue, int.MaxValue, mpos.ToCPos(map), CellStatus.Unvisited),
+					new Size(map.MapSize.X, map.MapSize.Y),
+					map.TileShape);
+		}
+
+		public PooledCellInfoLayer Get()
+		{
+			return new PooledCellInfoLayer(this);
+		}
+
+		CellLayer<CellInfo> GetLayer()
+		{
+			CellLayer<CellInfo> layer = null;
+			lock (pool)
+				if (pool.Count > 0)
+					layer = pool.Pop();
+
+			if (layer == null)
+				layer = new CellLayer<CellInfo>(defaultLayer.Shape, defaultLayer.Size);
+			layer.CopyValuesFrom(defaultLayer);
+			return layer;
+		}
+
+		void ReturnLayer(CellLayer<CellInfo> layer)
+		{
+			lock (pool)
+			   if (pool.Count < MaxPoolSize)
+					pool.Push(layer);
+		}
+
+		public class PooledCellInfoLayer : IDisposable
+		{
+			public CellLayer<CellInfo> Layer { get; private set; }
+			CellInfoLayerPool layerPool;
+
+			public PooledCellInfoLayer(CellInfoLayerPool layerPool)
+			{
+				this.layerPool = layerPool;
+				Layer = layerPool.GetLayer();
+			}
+
+			public void Dispose()
+			{
+				if (Layer == null)
+					return;
+				layerPool.ReturnLayer(Layer);
+				Layer = null;
+				layerPool = null;
+			}
+		}
+	}
+}

OpenRA.Mods.Common/Pathfinder/PathGraph.cs

@@ -69,7 +69,7 @@ namespace OpenRA.Mods.Common.Pathfinder
 		}
 	}
 
-	public class PathGraph : IGraph<CellInfo>
+	sealed class PathGraph : IGraph<CellInfo>
 	{
 		public Actor Actor { get; private set; }
 		public World World { get; private set; }
@@ -82,11 +82,13 @@ namespace OpenRA.Mods.Common.Pathfinder
 		readonly CellConditions checkConditions;
 		readonly MobileInfo mobileInfo;
 		readonly MobileInfo.WorldMovementInfo worldMovementInfo;
+		readonly CellInfoLayerPool.PooledCellInfoLayer pooledLayer;
 		CellLayer<CellInfo> cellInfo;
 
-		public PathGraph(CellLayer<CellInfo> cellInfo, MobileInfo mobileInfo, Actor actor, World world, bool checkForBlocked)
+		public PathGraph(CellInfoLayerPool layerPool, MobileInfo mobileInfo, Actor actor, World world, bool checkForBlocked)
 		{
-			this.cellInfo = cellInfo;
+			pooledLayer = layerPool.Get();
+			cellInfo = pooledLayer.Layer;
 			World = world;
 			this.mobileInfo = mobileInfo;
 			worldMovementInfo = mobileInfo.GetWorldMovementInfo(world);
@@ -174,26 +176,16 @@ namespace OpenRA.Mods.Common.Pathfinder
 			return cellCost;
 		}
 
-		bool disposed;
-		public void Dispose()
-		{
-			if (disposed)
-				return;
-
-			disposed = true;
-
-			CellInfoLayerManager.Instance.PutBackIntoPool(cellInfo);
-			cellInfo = null;
-
-			GC.SuppressFinalize(this);
-		}
-
-		~PathGraph() { Dispose(); }
-
 		public CellInfo this[CPos pos]
 		{
 			get { return cellInfo[pos]; }
 			set { cellInfo[pos] = value; }
 		}
+
+		public void Dispose()
+		{
+			pooledLayer.Dispose();
+			cellInfo = null;
+		}
 	}
 }

OpenRA.Mods.Common/Pathfinder/PathSearch.cs

@@ -11,6 +11,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using OpenRA.Mods.Common.Traits;
 using OpenRA.Primitives;
 
@@ -18,6 +19,14 @@ namespace OpenRA.Mods.Common.Pathfinder
 {
 	public sealed class PathSearch : BasePathSearch
 	{
+		static readonly ConditionalWeakTable<World, CellInfoLayerPool> LayerPoolTable = new ConditionalWeakTable<World, CellInfoLayerPool>();
+		static readonly ConditionalWeakTable<World, CellInfoLayerPool>.CreateValueCallback CreateLayerPool = world => new CellInfoLayerPool(world.Map);
+
+		static CellInfoLayerPool LayerPoolForWorld(World world)
+		{
+			return LayerPoolTable.GetValue(world, CreateLayerPool);
+		}
+
 		public override IEnumerable<Pair<CPos, int>> Considered
 		{
 			get { return considered; }
@@ -35,7 +44,7 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public static IPathSearch Search(World world, MobileInfo mi, Actor self, bool checkForBlocked, Func<CPos, bool> goalCondition)
 		{
-			var graph = new PathGraph(CellInfoLayerManager.Instance.NewLayer(world.Map), mi, self, world, checkForBlocked);
+			var graph = new PathGraph(LayerPoolForWorld(world), mi, self, world, checkForBlocked);
 			var search = new PathSearch(graph);
 			search.isGoal = goalCondition;
 			search.heuristic = loc => 0;
@@ -44,7 +53,7 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public static IPathSearch FromPoint(World world, MobileInfo mi, Actor self, CPos from, CPos target, bool checkForBlocked)
 		{
-			var graph = new PathGraph(CellInfoLayerManager.Instance.NewLayer(world.Map), mi, self, world, checkForBlocked);
+			var graph = new PathGraph(LayerPoolForWorld(world), mi, self, world, checkForBlocked);
 			var search = new PathSearch(graph)
 			{
 				heuristic = DefaultEstimator(target)
@@ -64,7 +73,7 @@ namespace OpenRA.Mods.Common.Pathfinder
 
 		public static IPathSearch FromPoints(World world, MobileInfo mi, Actor self, IEnumerable<CPos> froms, CPos target, bool checkForBlocked)
 		{
-			var graph = new PathGraph(CellInfoLayerManager.Instance.NewLayer(world.Map), mi, self, world, checkForBlocked);
+			var graph = new PathGraph(LayerPoolForWorld(world), mi, self, world, checkForBlocked);
 			var search = new PathSearch(graph)
 			{
 				heuristic = DefaultEstimator(target)

OpenRA.Mods.Common/Traits/Harvester.cs

@@ -165,9 +165,9 @@ namespace OpenRA.Mods.Common.Traits
 				select new { Location = r.Actor.Location + r.Trait.DeliveryOffset, Actor = r.Actor, Occupancy = linkedHarvs }).ToDictionary(r => r.Location);
 
 			// Start a search from each refinery's delivery location:
+			List<CPos> path;
 			var mi = self.Info.Traits.Get<MobileInfo>();
-			var path = self.World.WorldActor.Trait<IPathFinder>().FindPath(
-				PathSearch.FromPoints(self.World, mi, self, refs.Values.Select(r => r.Location), self.Location, false)
+			using (var search = PathSearch.FromPoints(self.World, mi, self, refs.Values.Select(r => r.Location), self.Location, false)
 				.WithCustomCost(loc =>
 				{
 					if (!refs.ContainsKey(loc))
@@ -181,7 +181,8 @@ namespace OpenRA.Mods.Common.Traits
 
 					// Prefer refineries with less occupancy (multiplier is to offset distance cost):
 					return occupancy * 12;
-					}));
+				}))
+				path = self.World.WorldActor.Trait<IPathFinder>().FindPath(search);
 
 			if (path.Count != 0)
 				return refs[path.Last()].Actor;

OpenRA.Mods.Common/Traits/World/PathFinder.cs

@@ -72,9 +72,10 @@ namespace OpenRA.Mods.Common.Traits
 					return EmptyPath;
 			}
 
-			var pb = FindBidiPath(
-				PathSearch.FromPoint(world, mi, self, target, source, true),
-				PathSearch.FromPoint(world, mi, self, source, target, true).Reverse());
+			List<CPos> pb;
+			using (var fromSrc = PathSearch.FromPoint(world, mi, self, target, source, true))
+			using (var fromDest = PathSearch.FromPoint(world, mi, self, source, target, true).Reverse())
+				pb = FindBidiPath(fromSrc, fromDest);
 
 			CheckSanePath2(pb, source, target);
 
@@ -106,11 +107,9 @@ namespace OpenRA.Mods.Common.Traits
 					return EmptyPath;
 			}
 
-			var path = FindBidiPath(
-				PathSearch.FromPoints(world, mi, self, tilesInRange, source, true),
-				PathSearch.FromPoint(world, mi, self, source, targetCell, true).Reverse());
-
-			return path;
+			using (var fromSrc = PathSearch.FromPoints(world, mi, self, tilesInRange, source, true))
+			using (var fromDest = PathSearch.FromPoint(world, mi, self, source, targetCell, true).Reverse())
+				return FindBidiPath(fromSrc, fromDest);
 		}
 
 		public List<CPos> FindPath(IPathSearch search)