Perf: Frozen environment variable caching

src/Build/BackEnd/BuildManager/BuildParameters.cs

@@ -1,9 +1,9 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
-using System.Collections.ObjectModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Threading;
@@ -129,7 +129,7 @@ public class BuildParameters : ITranslatable
         /// <summary>
         /// The original process environment.
         /// </summary>
-        private Dictionary<string, string> _buildProcessEnvironment;
+        private FrozenDictionary<string, string> _buildProcessEnvironment;
 
         /// <summary>
         /// The environment properties for the build.
@@ -282,9 +282,7 @@ internal BuildParameters(BuildParameters other, bool resetEnvironment = false)
             _enableRarNode = other._enableRarNode;
             _buildProcessEnvironment = resetEnvironment
                 ? CommunicationsUtilities.GetEnvironmentVariables()
-                : other._buildProcessEnvironment != null
-                    ? new Dictionary<string, string>(other._buildProcessEnvironment)
-                    : null;
+                : other._buildProcessEnvironment;
             _environmentProperties = other._environmentProperties != null ? new PropertyDictionary<ProjectPropertyInstance>(other._environmentProperties) : null;
             _forwardingLoggers = other._forwardingLoggers != null ? new List<ForwardingLoggerRecord>(other._forwardingLoggers) : null;
             _globalProperties = other._globalProperties != null ? new PropertyDictionary<ProjectPropertyInstance>(other._globalProperties) : null;
@@ -356,8 +354,7 @@ public bool UseSynchronousLogging
         /// <summary>
         /// Gets the environment variables which were set when this build was created.
         /// </summary>
-        public IDictionary<string, string> BuildProcessEnvironment => new ReadOnlyDictionary<string, string>(
-            _buildProcessEnvironment ?? new Dictionary<string, string>(0));
+        public IDictionary<string, string> BuildProcessEnvironment => BuildProcessEnvironmentInternal;
 
         /// <summary>
         /// The name of the culture to use during the build.
@@ -720,6 +717,8 @@ internal int BuildId
             set => _buildId = value;
         }
 
+        internal FrozenDictionary<string, string> BuildProcessEnvironmentInternal => _buildProcessEnvironment ?? FrozenDictionary<string, string>.Empty;
+
         /// <summary>
         /// Gets or sets the environment properties.
         /// </summary>

src/Build/BackEnd/Components/RequestBuilder/RequestBuilder.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
@@ -1378,7 +1379,7 @@ private void InitializeOperatingEnvironment()
             else
             {
                 // Restore the original build environment variables.
-                SetEnvironmentVariableBlock(_componentHost.BuildParameters.BuildProcessEnvironment);
+                SetEnvironmentVariableBlock(_componentHost.BuildParameters.BuildProcessEnvironmentInternal);
             }
         }
 
@@ -1401,17 +1402,17 @@ private void RestoreOperatingEnvironment()
         /// <summary>
         /// Sets the environment block to the set of saved variables.
         /// </summary>
-        private void SetEnvironmentVariableBlock(IDictionary<string, string> savedEnvironment)
+        private void SetEnvironmentVariableBlock(FrozenDictionary<string, string> savedEnvironment)
         {
-            IDictionary<string, string> currentEnvironment = CommunicationsUtilities.GetEnvironmentVariables();
+            FrozenDictionary<string, string> currentEnvironment = CommunicationsUtilities.GetEnvironmentVariables();
             ClearVariablesNotInEnvironment(savedEnvironment, currentEnvironment);
             UpdateEnvironmentVariables(savedEnvironment, currentEnvironment);
         }
 
         /// <summary>
         /// Clears from the current environment any variables which do not exist in the saved environment
         /// </summary>
-        private void ClearVariablesNotInEnvironment(IDictionary<string, string> savedEnvironment, IDictionary<string, string> currentEnvironment)
+        private void ClearVariablesNotInEnvironment(FrozenDictionary<string, string> savedEnvironment, FrozenDictionary<string, string> currentEnvironment)
         {
             foreach (KeyValuePair<string, string> entry in currentEnvironment)
             {
@@ -1425,7 +1426,7 @@ private void ClearVariablesNotInEnvironment(IDictionary<string, string> savedEnv
         /// <summary>
         /// Updates the current environment with values in the saved environment which differ or are not yet set.
         /// </summary>
-        private void UpdateEnvironmentVariables(IDictionary<string, string> savedEnvironment, IDictionary<string, string> currentEnvironment)
+        private void UpdateEnvironmentVariables(FrozenDictionary<string, string> savedEnvironment, FrozenDictionary<string, string> currentEnvironment)
         {
             foreach (KeyValuePair<string, string> entry in savedEnvironment)
             {

src/Build/BackEnd/Node/InProcNode.cs

@@ -1,9 +1,9 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
 using System.Collections.Concurrent;
-using System.Collections.Generic;
+using System.Collections.Frozen;
 using System.Globalization;
 using System.Threading;
 using Microsoft.Build.BackEnd.Components.Caching;
@@ -31,7 +31,7 @@ internal class InProcNode : INode, INodePacketFactory
         /// <summary>
         /// The environment at the time the build is started.
         /// </summary>
-        private IDictionary<string, string> _savedEnvironment;
+        private FrozenDictionary<string, string> _savedEnvironment;
 
         /// <summary>
         /// The current directory at the time the build is started.

src/Build/BackEnd/Node/OutOfProcNode.cs

@@ -1,8 +1,9 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Globalization;
@@ -50,7 +51,7 @@ public class OutOfProcNode : INode, IBuildComponentHost, INodePacketFactory, INo
         /// <summary>
         /// The saved environment for the process.
         /// </summary>
-        private IDictionary<string, string> _savedEnvironment;
+        private FrozenDictionary<string, string> _savedEnvironment;
 
         /// <summary>
         /// The component factories.

src/Build/BackEnd/Shared/BuildRequestConfiguration.cs

@@ -1,7 +1,8 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Globalization;
@@ -131,7 +132,7 @@ internal class BuildRequestConfiguration : IEquatable<BuildRequestConfiguration>
         /// <summary>
         /// Holds a snapshot of the environment at the time we blocked.
         /// </summary>
-        private Dictionary<string, string> _savedEnvironmentVariables;
+        private FrozenDictionary<string, string> _savedEnvironmentVariables;
 
         /// <summary>
         /// Holds a snapshot of the current working directory at the time we blocked.
@@ -611,7 +612,7 @@ public Lookup BaseLookup
         /// <summary>
         /// Holds a snapshot of the environment at the time we blocked.
         /// </summary>
-        public Dictionary<string, string> SavedEnvironmentVariables
+        public FrozenDictionary<string, string> SavedEnvironmentVariables
         {
             get => _savedEnvironmentVariables;
 

src/Build/BackEnd/Shared/BuildResult.cs

@@ -1,8 +1,9 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
@@ -107,7 +108,7 @@ public class BuildResult : BuildResultBase, INodePacket, IBuildResults
         /// Snapshot of the environment from the configuration this results comes from.
         /// This should only be populated when the configuration for this result is moved between nodes.
         /// </summary>
-        private Dictionary<string, string>? _savedEnvironmentVariables;
+        private FrozenDictionary<string, string>? _savedEnvironmentVariables;
 
         /// <summary>
         /// When this key is in the dictionary <see cref="_savedEnvironmentVariables"/>, serialize the build result version.
@@ -437,7 +438,7 @@ NodePacketType INodePacket.Type
         /// <summary>
         /// Holds a snapshot of the environment at the time we blocked.
         /// </summary>
-        Dictionary<string, string>? IBuildResults.SavedEnvironmentVariables
+        FrozenDictionary<string, string>? IBuildResults.SavedEnvironmentVariables
         {
             get => _savedEnvironmentVariables;
 
@@ -655,6 +656,7 @@ void ITranslatable.Translate(ITranslator translator)
             }
             else
             {
+                IDictionary<string, string>? savedEnvironmentVariables = _savedEnvironmentVariables;
                 Dictionary<string, string> additionalEntries = new();
 
                 if (translator.Mode == TranslationDirection.WriteToStream)
@@ -663,15 +665,16 @@ void ITranslatable.Translate(ITranslator translator)
                     additionalEntries.Add(SpecialKeyForVersion, String.Empty);
 
                     // Serialize the special key together with _savedEnvironmentVariables dictionary using the workaround overload of TranslateDictionary:
-                    translator.TranslateDictionary(ref _savedEnvironmentVariables, StringComparer.OrdinalIgnoreCase, ref additionalEntries, s_additionalEntriesKeys);
+                    translator.TranslateDictionary(ref savedEnvironmentVariables, StringComparer.OrdinalIgnoreCase, ref additionalEntries, s_additionalEntriesKeys);
 
                     // Serialize version
                     translator.Translate(ref _version);
                 }
                 else if (translator.Mode == TranslationDirection.ReadFromStream)
                 {
                     // Read the dictionary using the workaround overload of TranslateDictionary: special keys (additionalEntriesKeys) would be read to additionalEntries instead of the _savedEnvironmentVariables dictionary.
-                    translator.TranslateDictionary(ref _savedEnvironmentVariables, StringComparer.OrdinalIgnoreCase, ref additionalEntries, s_additionalEntriesKeys);
+                    translator.TranslateDictionary(ref savedEnvironmentVariables, StringComparer.OrdinalIgnoreCase, ref additionalEntries, s_additionalEntriesKeys);
+                    _savedEnvironmentVariables = savedEnvironmentVariables?.ToFrozenDictionary(StringComparer.OrdinalIgnoreCase);
 
                     // If the special key SpecialKeyForVersion present in additionalEntries, also read a version, otherwise set it to 0.
                     if (additionalEntries is not null && additionalEntries.ContainsKey(SpecialKeyForVersion))

src/Build/BackEnd/Shared/IBuildResults.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using Microsoft.Build.Execution;
 
@@ -32,7 +33,7 @@ internal interface IBuildResults
         /// <summary>
         /// Set of environment variables for the configuration this result came from
         /// </summary>
-        Dictionary<string, string> SavedEnvironmentVariables { get; set; }
+        FrozenDictionary<string, string> SavedEnvironmentVariables { get; set; }
 
         /// <summary>
         /// The current directory for the configuration this result came from

src/Framework/BinaryTranslator.cs

@@ -601,7 +601,7 @@ public void TranslateDictionary(ref Dictionary<string, string> dictionary, IEqua
             /// This overload is needed for a workaround concerning serializing BuildResult with a version.
             /// It deserializes additional entries together with the main dictionary.
             /// </remarks>
-            public void TranslateDictionary(ref Dictionary<string, string> dictionary, IEqualityComparer<string> comparer, ref Dictionary<string, string> additionalEntries, HashSet<string> additionalEntriesKeys)
+            public void TranslateDictionary(ref IDictionary<string, string> dictionary, IEqualityComparer<string> comparer, ref Dictionary<string, string> additionalEntries, HashSet<string> additionalEntriesKeys)
             {
                 if (!TranslateNullable(dictionary))
                 {
@@ -1383,7 +1383,7 @@ public void TranslateDictionary(ref Dictionary<string, string> dictionary, IEqua
             /// This overload is needed for a workaround concerning serializing BuildResult with a version.
             /// It serializes additional entries together with the main dictionary.
             /// </remarks>
-            public void TranslateDictionary(ref Dictionary<string, string> dictionary, IEqualityComparer<string> comparer, ref Dictionary<string, string> additionalEntries, HashSet<string> additionalEntriesKeys)
+            public void TranslateDictionary(ref IDictionary<string, string> dictionary, IEqualityComparer<string> comparer, ref Dictionary<string, string> additionalEntries, HashSet<string> additionalEntriesKeys)
             {
                 // Translate whether object is null
                 if ((dictionary is null) && ((additionalEntries is null) || (additionalEntries.Count == 0)))

src/Framework/ITranslator.cs

@@ -318,7 +318,7 @@ void TranslateArray<T>(ref T[] array)
         /// This overload is needed for a workaround concerning serializing BuildResult with a version.
         /// It serializes/deserializes additional entries together with the main dictionary.
         /// </remarks>
-        void TranslateDictionary(ref Dictionary<string, string> dictionary, IEqualityComparer<string> comparer, ref Dictionary<string, string> additionalEntries, HashSet<string> additionalEntriesKeys);
+        void TranslateDictionary(ref IDictionary<string, string> dictionary, IEqualityComparer<string> comparer, ref Dictionary<string, string> additionalEntries, HashSet<string> additionalEntriesKeys);
 
         void TranslateDictionary(ref IDictionary<string, string> dictionary, NodePacketCollectionCreator<IDictionary<string, string>> collectionCreator);