thompson-tomo · pull · Jun 19, 2025 · Jun 19, 2025 · Jun 19, 2025 · Jun 19, 2025
diff --git a/src/Build.UnitTests/BackEnd/Scheduler_Tests.cs b/src/Build.UnitTests/BackEnd/Scheduler_Tests.cs
@@ -18,13 +18,13 @@
 
 namespace Microsoft.Build.UnitTests.BackEnd
 {
+    using System.Linq;
+    using FluentAssertions;
     using Microsoft.Build.Unittest;
 
     /// <summary>
     /// Tests of the scheduler.
     /// </summary>
-    // Ignore: Causing issues with other tests
-    // NOTE: marked as "internal" to disable the entire test class, as was done for MSTest.
     public class Scheduler_Tests : IDisposable
     {
         /// <summary>
@@ -57,6 +57,11 @@ public class Scheduler_Tests : IDisposable
         /// </summary>
         private BuildParameters _parameters;
 
+        /// <summary>
+        /// Configuration ID.
+        /// </summary>
+        private const int DefaultConfigId = 99;
+
         /// <summary>
         /// Set up
         /// </summary>
@@ -70,8 +75,8 @@ public Scheduler_Tests()
             _host = new MockHost();
             _scheduler = new Scheduler();
             _scheduler.InitializeComponent(_host);
-            CreateConfiguration(99, "parent.proj");
-            _defaultParentRequest = CreateBuildRequest(99, 99, Array.Empty<string>(), null);
+            CreateConfiguration(DefaultConfigId, "parent.proj");
+            _defaultParentRequest = CreateBuildRequest(99, DefaultConfigId, Array.Empty<string>(), null);
 
             // Set up the scheduler with one node to start with.
             _scheduler.ReportNodesCreated(new NodeInfo[] { new NodeInfo(1, NodeProviderType.InProc) });
@@ -386,8 +391,8 @@ public void VerifyRequestOrderingDoesNotAffectNodeCreationCountWithInProcAndAnyR
             _parameters.ShutdownInProcNodeOnBuildFinish = true;
             _buildManager = new BuildManager();
 
-            CreateConfiguration(99, "parent.proj");
-            _defaultParentRequest = CreateBuildRequest(99, 99, Array.Empty<string>(), null);
+            CreateConfiguration(DefaultConfigId, "parent.proj");
+            _defaultParentRequest = CreateBuildRequest(99, DefaultConfigId, Array.Empty<string>(), null);
 
             CreateConfiguration(1, "foo.proj");
             BuildRequest request1 = CreateBuildRequest(1, 1, new string[] { "foo" }, NodeAffinity.Any, _defaultParentRequest);
@@ -578,8 +583,8 @@ public void VerifyNoOverCreationOfNodesWithBuildLoop()
             _parameters.ShutdownInProcNodeOnBuildFinish = true;
             _buildManager = new BuildManager();
 
-            CreateConfiguration(99, "parent.proj");
-            _defaultParentRequest = CreateBuildRequest(99, 99, Array.Empty<string>(), null);
+            CreateConfiguration(DefaultConfigId, "parent.proj");
+            _defaultParentRequest = CreateBuildRequest(99, DefaultConfigId, Array.Empty<string>(), null);
 
             CreateConfiguration(1, "foo.proj");
             BuildRequest request1 = CreateBuildRequest(1, 1, new string[] { "foo" }, NodeAffinity.OutOfProc, _defaultParentRequest);
@@ -768,12 +773,13 @@ private BuildResult CacheBuildResult(BuildRequest request, string target, WorkUn
         }
 
         /// <summary>
-        /// Creates a build result for a request
+        /// Creates a build result for a request.
         /// </summary>
         private BuildResult CreateBuildResult(BuildRequest request, string target, WorkUnitResult workUnitResult)
         {
             BuildResult result = new BuildResult(request);
             result.AddResultsForTarget(target, new TargetResult(Array.Empty<TaskItem>(), workUnitResult));
+
             return result;
         }
 
@@ -788,23 +794,30 @@ private BuildRequest CreateBuildRequest(int nodeRequestId, int configId)
         /// <summary>
         /// Creates a build request.
         /// </summary>
-        private BuildRequest CreateBuildRequest(int nodeRequestId, int configId, string[] targets)
+        private BuildRequest CreateBuildRequest(int nodeRequestId, int configId, string[] targets, BuildRequestDataFlags buildRequestDataFlags = BuildRequestDataFlags.None)
         {
-            return CreateBuildRequest(nodeRequestId, configId, targets, _defaultParentRequest);
+            return CreateBuildRequest(nodeRequestId, configId, targets, _defaultParentRequest, buildRequestDataFlags);
         }
 
         /// <summary>
         /// Creates a build request.
         /// </summary>
-        private BuildRequest CreateBuildRequest(int nodeRequestId, int configId, string[] targets, BuildRequest parentRequest)
+        private BuildRequest CreateBuildRequest(int nodeRequestId, int configId, string[] targets, BuildRequest parentRequest, BuildRequestDataFlags buildRequestDataFlags = BuildRequestDataFlags.None)
         {
-            return CreateBuildRequest(nodeRequestId, configId, targets, NodeAffinity.Any, parentRequest);
+            return CreateBuildRequest(nodeRequestId, configId, targets, NodeAffinity.Any, parentRequest, buildRequestDataFlags: buildRequestDataFlags);
         }
 
         /// <summary>
         /// Creates a build request.
         /// </summary>
-        private BuildRequest CreateBuildRequest(int nodeRequestId, int configId, string[] targets, NodeAffinity nodeAffinity, BuildRequest parentRequest, ProxyTargets proxyTargets = null)
+        private BuildRequest CreateBuildRequest(
+            int nodeRequestId,
+            int configId,
+            string[] targets,
+            NodeAffinity nodeAffinity,
+            BuildRequest parentRequest,
+            ProxyTargets proxyTargets = null,
+            BuildRequestDataFlags buildRequestDataFlags = BuildRequestDataFlags.None)
         {
             (targets == null ^ proxyTargets == null).ShouldBeTrue();
 
@@ -825,16 +838,19 @@ private BuildRequest CreateBuildRequest(int nodeRequestId, int configId, string[
                     targets,
                     hostServices,
                     BuildEventContext.Invalid,
-                    parentRequest);
+                    parentRequest,
+                    buildRequestDataFlags: buildRequestDataFlags);
             }
 
             parentRequest.ShouldBeNull();
+
             return new BuildRequest(
                 submissionId: 1,
                 nodeRequestId,
                 configId,
                 proxyTargets,
-                hostServices);
+                hostServices,
+                buildRequestDataFlags: buildRequestDataFlags);
         }
 
         private BuildRequest CreateProxyBuildRequest(int nodeRequestId, int configId, ProxyTargets proxyTargets, BuildRequest parentRequest)
@@ -848,6 +864,69 @@ private BuildRequest CreateProxyBuildRequest(int nodeRequestId, int configId, Pr
                 proxyTargets);
         }
 
+        /// <summary>
+        /// The test checks how scheduler handles the duplicated requests and cache MISS for this case.
+        /// It's expected to have the duplicated request rescheduled for the execution.
+        /// </summary>
+        [Fact]
+        public void ReportResultTest_NoCacheHitForDupes()
+        {
+            // Create a duplicate of the existing _defaultParentRequest, but with a different build request flag, so we can't get the result from the cache.
+            BuildRequest duplicateRequest = CreateBuildRequest(2, configId: DefaultConfigId, Array.Empty<string>(), parentRequest: null, BuildRequestDataFlags.ProvideSubsetOfStateAfterBuild);
+
+            // Schedule the duplicate request -> it goes to unscheduled request due to duplicated configId
+            _scheduler.ReportRequestBlocked(2, new BuildRequestBlocker(-1, Array.Empty<string>(), [duplicateRequest]));
+
+            // try to get a result for the parent request and see if we get a result for the duplicate request
+            var results = _scheduler.ReportResult(1, CreateBuildResult(_defaultParentRequest, "", BuildResultUtilities.GetSuccessResult()))
+                .ToList();
+
+            results.ShouldNotBeNull();
+            results.Count.ShouldBe(2);
+
+            // Completed _defaultParentRequest
+            results[0].BuildResult.ShouldNotBeNull();
+            results[0].BuildResult.BuildRequestDataFlags.ShouldBe(BuildRequestDataFlags.None);
+            results[0].Action.ShouldBe(ScheduleActionType.SubmissionComplete);
+
+            // The automatically scheduled duplicated request.
+            results[1].BuildResult.ShouldBeNull();
+            results[1].NodeId.Should().Be(1);
+            results[1].Action.ShouldBe(ScheduleActionType.Schedule);
+            results[1].BuildRequest.BuildRequestDataFlags.ShouldBe(BuildRequestDataFlags.ProvideSubsetOfStateAfterBuild);
+        }
+
+        /// <summary>
+        /// The test checks how scheduler handles the duplicated requests and cache HIT for this case.
+        /// It's expected to have an immediate result for the duplicated request.
+        /// </summary>
+        [Fact]
+        public void ReportResultTest_CacheHitForDupes()
+        {
+            // Create a duplicate of the existing _defaultParentRequest.
+            BuildRequest duplicateRequest = CreateBuildRequest(2, configId: DefaultConfigId, Array.Empty<string>(), parentRequest: null, BuildRequestDataFlags.None);
+
+            // Schedule the duplicate request -> it goes to unscheduled request due to duplicated configId
+            _scheduler.ReportRequestBlocked(1, new BuildRequestBlocker(-1, Array.Empty<string>(), [duplicateRequest]));
+
+            // try to get a result for the parent request and see if we get a result for the duplicate request.
+            var results = _scheduler.ReportResult(1, CreateBuildResult(duplicateRequest, "", BuildResultUtilities.GetSuccessResult()))
+                .ToList();
+
+            results.ShouldNotBeNull();
+            results.Count.ShouldBe(2);
+
+            // Completed _defaultParentRequest
+            results[0].BuildResult.ShouldNotBeNull();
+            results[0].BuildResult.BuildRequestDataFlags.ShouldBe(BuildRequestDataFlags.None);
+            results[0].Action.ShouldBe(ScheduleActionType.SubmissionComplete);
+
+            // We hit cache and completed the duplicate request.
+            results[1].BuildResult.ShouldNotBeNull();
+            results[1].BuildResult.BuildRequestDataFlags.ShouldBe(BuildRequestDataFlags.None);
+            results[1].Action.ShouldBe(ScheduleActionType.SubmissionComplete);
+        }
+
         /// <summary>
         /// Method that fakes the actions done by BuildManager.PerformSchedulingActions
         /// </summary>

diff --git a/src/Build/BackEnd/BuildManager/BuildManager.cs b/src/Build/BackEnd/BuildManager/BuildManager.cs
@@ -2427,8 +2427,8 @@ private void HandleNewRequest(int node, BuildRequestBlocker blocker)
                 }
             }
 
-            IEnumerable<ScheduleResponse> response = _scheduler!.ReportRequestBlocked(node, blocker);
-            PerformSchedulingActions(response);
+            IEnumerable<ScheduleResponse> responses = _scheduler!.ReportRequestBlocked(node, blocker);
+            PerformSchedulingActions(responses);
         }
 
         /// <summary>

diff --git a/src/Build/BackEnd/BuildManager/BuildParameters.cs b/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>

diff --git a/src/Build/BackEnd/Components/RequestBuilder/RequestBuilder.cs b/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)
             {