[Core] Refactor a bit of list pooling to optimize for common case

3 files changed, 56 insertions, 3 deletions

diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj
index 49fdc36721..e9ffce8362 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj
@@ -733,6 +733,7 @@
     <Compile Include="MonoDevelop.Projects.MSBuild\MSBuildSdkProject.cs" />
     <Compile Include="MonoDevelop.Projects\SdkProjectShortTargetFramework.cs" />
     <Compile Include="MonoDevelop.Utilities\SampleProfiler.cs" />
+    <Compile Include="MonoDevelop.Core\PooledListPolicy.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="BuildVariables.cs.in" />
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core/PooledListPolicy.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core/PooledListPolicy.cs
new file mode 100644
index 0000000000..a6d88f3df6
--- /dev/null
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core/PooledListPolicy.cs
@@ -0,0 +1,48 @@
+//
+// PooledListPolicy.cs
+//
+// Author:
+//       Marius Ungureanu <maungu@microsoft.com>
+//
+// Copyright (c) 2019 Microsoft Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+using System;
+using System.Collections.Generic;
+using Microsoft.Extensions.ObjectPool;
+
+namespace MonoDevelop.Core
+{
+	sealed class PooledListPolicy<T> : PooledObjectPolicy<List<T>>
+	{
+		public int InitialCapacity { get; set; } = 8;
+		public int MaximumRetainedCapacity { get; set; } = 32;
+
+		public override List<T> Create () => new List<T> (InitialCapacity);
+
+		public override bool Return (List<T> obj)
+		{
+			if (obj.Capacity > MaximumRetainedCapacity)
+				obj.Capacity = MaximumRetainedCapacity;
+
+			obj.Clear ();
+			return true;
+		}
+	}
+}
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs
index 1054338175..45139f8c57 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs
@@ -4614,7 +4614,8 @@ namespace MonoDevelop.Projects
 			});
 		}
 
-		static readonly ObjectPool<List<(FilePath, ProjectItem)>> projectItemListPool = ObjectPool.Create<List<(FilePath, ProjectItem)>> ();
+		static readonly ObjectPool<List<(FilePath, ProjectItem)>> projectItemListPool
+			= ObjectPool.Create (new PooledListPolicy<(FilePath, ProjectItem)> { MaximumRetainedCapacity = 8, InitialCapacity = 4 });
 
 		void OnFileCreatedExternally (FilePath fileName)
 		{
@@ -4649,15 +4650,19 @@ namespace MonoDevelop.Projects
 			if (!UseAdvancedGlobSupport)
 				globItems = globItems.Where (it => !it.Metadata.GetProperties ().Any ());
 
-			var list = projectItemListPool.Get ();
+			List<(FilePath, ProjectItem)> list = null;
 			foreach (var it in globItems) {
 				var eit = CreateFakeEvaluatedItem (sourceProject, it, include, null);
 				var pi = CreateProjectItem (eit);
 				pi.Read (this, eit);
 
+				list ??= projectItemListPool.Get ();
 				list.Add ((fileName, pi));
 			}
 
+			if (list == null)
+				return;
+
 			Runtime.RunInMainThread (() => {
 				// Double check the file has not been added on the UI thread by the IDE.
 				try {
@@ -4665,7 +4670,6 @@ namespace MonoDevelop.Projects
 					if (list.Count > 0)
 						Items.AddRange (list.Select (item => item.Item2));
 				} finally {
-					list.Clear ();
 					projectItemListPool.Return (list);
 				}
 			}).Ignore ();