fixed #5203 by caching boxed object only once and re-use them

src/VisualStudio/Core/Def/Implementation/TableDataSource/ValueTypeCache.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Concurrent;
+
+namespace Microsoft.VisualStudio.LanguageServices.Implementation.TableDataSource
+{
+    internal static class ValueTypeCache
+    {
+        /// <summary>
+        /// Re-use already boxed object for value type.
+        /// this cache never release cached object. must be used only with fixed set of valut types. or
+        /// something that grows very slowly like Guid for projects.
+        /// </summary>
+        public static object GetOrCreate<T>(T value) where T : struct
+        {
+            // let compiler creates a cache for each value type.
+            return Cache<T>.Instance.GetOrCreate(value);
+        }
+
+        private class Cache<T> where T : struct
+        {
+            public static readonly Cache<T> Instance = new Cache<T>();
+
+            private static readonly Func<T, object> _boxer = v => (object)v;
+
+            // this will be never released, must be used only for fixed size set
+            private readonly ConcurrentDictionary<T, object> _map =
+                new ConcurrentDictionary<T, object>(concurrencyLevel: 2, capacity: 5);
+
+            public object GetOrCreate(T value)
+            {
+                return _map.GetOrAdd(value, _boxer);
+            }
+        }
+    }
+}
\ No newline at end of file

src/VisualStudio/Core/Def/Implementation/TableDataSource/VisualStudioBaseDiagnosticListTable.LiveTableDataSource.cs

@@ -257,10 +257,10 @@ public override bool TryGetValue(int index, string columnName, out object conten
                     switch (columnName)
                     {
                         case StandardTableKeyNames.ErrorRank:
-                            content = GetErrorRank(data);
+                            content = ValueTypeCache.GetOrCreate(GetErrorRank(data));
                             return true;
                         case StandardTableKeyNames.ErrorSeverity:
-                            content = GetErrorCategory(data.Severity);
+                            content = ValueTypeCache.GetOrCreate(GetErrorCategory(data.Severity));
                             return true;
                         case StandardTableKeyNames.ErrorCode:
                             content = data.Id;
@@ -275,7 +275,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                             content = data.Category;
                             return true;
                         case StandardTableKeyNames.ErrorSource:
-                            content = GetErrorSource(_source.BuildTool);
+                            content = ValueTypeCache.GetOrCreate(GetErrorSource(_source.BuildTool));
                             return true;
                         case StandardTableKeyNames.BuildTool:
                             content = GetBuildTool(_source.BuildTool);
@@ -299,7 +299,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                             content = item.ProjectNames;
                             return ((string[])content).Length > 0;
                         case StandardTableKeyNames.ProjectGuid:
-                            content = item.ProjectGuid;
+                            content = ValueTypeCache.GetOrCreate(item.ProjectGuid);
                             return (Guid)content != Guid.Empty;
                         case ProjectGuids:
                             content = item.ProjectGuids;

src/VisualStudio/Core/Def/Implementation/TableDataSource/VisualStudioBaseTodoListTable.cs

@@ -235,7 +235,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                     switch (columnName)
                     {
                         case StandardTableKeyNames.Priority:
-                            content = (VSTASKPRIORITY)data.Priority;
+                            content = ValueTypeCache.GetOrCreate((VSTASKPRIORITY)data.Priority);
                             return true;
                         case StandardTableKeyNames.Text:
                             content = data.Message;
@@ -250,7 +250,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                             content = GetLineColumn(data).Character;
                             return true;
                         case StandardTableKeyNames.TaskCategory:
-                            content = VSTASKCATEGORY.CAT_COMMENTS;
+                            content = ValueTypeCache.GetOrCreate(VSTASKCATEGORY.CAT_COMMENTS);
                             return true;
                         case StandardTableKeyNames.ProjectName:
                             content = item.ProjectName;
@@ -259,7 +259,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                             content = item.ProjectNames;
                             return ((string[])content).Length > 0;
                         case StandardTableKeyNames.ProjectGuid:
-                            content = item.ProjectGuid;
+                            content = ValueTypeCache.GetOrCreate(item.ProjectGuid);
                             return (Guid)content != Guid.Empty;
                         case ProjectGuids:
                             content = item.ProjectGuids;

src/VisualStudio/Core/Def/Implementation/TableDataSource/VisualStudioDiagnosticListTable.BuildTableDataSource.cs

@@ -180,10 +180,11 @@ public override bool TryGetValue(int index, string columnName, out object conten
                     switch (columnName)
                     {
                         case StandardTableKeyNames.ErrorRank:
-                            content = WellKnownDiagnosticTags.Build;
+                            // build error gets highest rank
+                            content = ValueTypeCache.GetOrCreate(ErrorRank.Lexical);
                             return true;
                         case StandardTableKeyNames.ErrorSeverity:
-                            content = GetErrorCategory(data.Severity);
+                            content = ValueTypeCache.GetOrCreate(GetErrorCategory(data.Severity));
                             return true;
                         case StandardTableKeyNames.ErrorCode:
                             content = data.Id;
@@ -198,7 +199,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                             content = data.Category;
                             return true;
                         case StandardTableKeyNames.ErrorSource:
-                            content = ErrorSource.Build;
+                            content = ValueTypeCache.GetOrCreate(ErrorSource.Build);
                             return true;
                         case StandardTableKeyNames.BuildTool:
                             content = _source.BuildTool;
@@ -222,7 +223,7 @@ public override bool TryGetValue(int index, string columnName, out object conten
                             content = item.ProjectNames;
                             return ((string[])content).Length > 0;
                         case StandardTableKeyNames.ProjectGuid:
-                            content = item.ProjectGuid;
+                            content = ValueTypeCache.GetOrCreate(item.ProjectGuid);
                             return (Guid)content != Guid.Empty;
                         case ProjectGuids:
                             content = item.ProjectGuids;

src/VisualStudio/Core/Def/ServicesVisualStudio.csproj

@@ -78,6 +78,7 @@
     <Compile Include="Implementation\ProjectInfo\DefaultProjectInfoServiceFactory.cs" />
     <Compile Include="Implementation\TableDataSource\MiscTodoListTableControlEventProcessorProvider.cs" />
     <Compile Include="Implementation\TableDataSource\UriNavigator.cs" />
+    <Compile Include="Implementation\TableDataSource\ValueTypeCache.cs" />
     <Compile Include="Implementation\TableDataSource\VisualStudioBaseDiagnosticListTable.LiveTableDataSource.cs" />
     <Compile Include="Implementation\TableDataSource\VisualStudioDiagnosticListTable.BuildTableDataSource.cs" />
     <Compile Include="Implementation\TableDataSource\VisualStudioDiagnosticListTable.cs" />