*** WIP: Optimize work done in ProjectCodeModelFactory

src/EditorFeatures/Core/EditAndContinue/PdbMatchingSourceTextProvider.cs

@@ -30,14 +30,20 @@ internal sealed class PdbMatchingSourceTextProvider() : IEventListener, IPdbMatc
     private bool _isActive;
     private int _baselineSolutionVersion;
     private readonly Dictionary<string, (DocumentState state, int solutionVersion)> _documentsWithChangedLoaderByPath = [];
+    private WorkspaceEventRegistration? _workspaceChangedDisposer;
 
     public void StartListening(Workspace workspace)
-        => workspace.WorkspaceChanged += WorkspaceChanged;
+    {
+        _workspaceChangedDisposer = workspace.RegisterWorkspaceChangedHandler(WorkspaceChanged);
+    }
 
     public void StopListening(Workspace workspace)
-        => workspace.WorkspaceChanged -= WorkspaceChanged;
+    {
+        _workspaceChangedDisposer?.Dispose();
+        _workspaceChangedDisposer = null;
+    }
 
-    private void WorkspaceChanged(object? sender, WorkspaceChangeEventArgs e)
+    private void WorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         if (!_isActive)
         {

src/EditorFeatures/Core/EditorConfigSettings/Aggregator/SettingsAggregator.cs

@@ -32,7 +32,7 @@ public SettingsAggregator(
         IAsynchronousOperationListener listener)
     {
         _workspace = workspace;
-        _workspace.WorkspaceChanged += UpdateProviders;
+        _ = workspace.RegisterWorkspaceChangedHandler(UpdateProviders);
 
         var currentSolution = _workspace.CurrentSolution.SolutionState;
         UpdateProviders(currentSolution);
@@ -48,7 +48,7 @@ public SettingsAggregator(
             threadingContext.DisposalToken);
     }
 
-    private void UpdateProviders(object? sender, WorkspaceChangeEventArgs e)
+    private void UpdateProviders(WorkspaceChangeEventArgs e)
     {
         switch (e.Kind)
         {

src/EditorFeatures/Core/InlineRename/InlineRenameSession.cs

@@ -57,6 +57,7 @@ internal sealed partial class InlineRenameSession : IInlineRenameSession, IFeatu
     private bool _isApplyingEdit;
     private string _replacementText;
     private readonly Dictionary<ITextBuffer, OpenTextBufferManager> _openTextBuffers = [];
+    private WorkspaceEventRegistration _workspaceChangedDisposer;
 
     /// <summary>
     /// The original <see cref="Document"/> where rename was triggered
@@ -161,7 +162,9 @@ public InlineRenameSession(
         _inlineRenameSessionDurationLogBlock = Logger.LogBlock(FunctionId.Rename_InlineSession, CancellationToken.None);
 
         Workspace = workspace;
-        Workspace.WorkspaceChanged += OnWorkspaceChanged;
+
+        // Requires the main thread due to OnWorkspaceChanged calling the Cancel method
+        _workspaceChangedDisposer = workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged, WorkspaceEventOptions.RequiresMainThreadOptions);
 
         _textBufferFactoryService = textBufferFactoryService;
         _textBufferCloneService = textBufferCloneService;
@@ -383,7 +386,7 @@ private void VerifyNotDismissed()
         }
     }
 
-    private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs args)
+    private void OnWorkspaceChanged(WorkspaceChangeEventArgs args)
     {
         if (args.Kind != WorkspaceChangeKind.DocumentChanged)
         {
@@ -701,7 +704,9 @@ private void DismissUIAndRollbackEditsAndEndRenameSession_MustBeCalledOnUIThread
 
         void DismissUIAndRollbackEdits()
         {
-            Workspace.WorkspaceChanged -= OnWorkspaceChanged;
+            _workspaceChangedDisposer?.Dispose();
+            _workspaceChangedDisposer = null;
+
             _textBufferAssociatedViewService.SubjectBuffersConnected -= OnSubjectBuffersConnected;
 
             // Reenable completion now that the inline rename session is done

src/EditorFeatures/Core/Shared/Tagging/EventSources/TaggerEventSources.ParseOptionChangedEventSource.cs

@@ -13,13 +13,20 @@ internal partial class TaggerEventSources
 {
     private sealed class ParseOptionChangedEventSource(ITextBuffer subjectBuffer) : AbstractWorkspaceTrackingTaggerEventSource(subjectBuffer)
     {
+        private WorkspaceEventRegistration? _workspaceChangedDisposer;
+
         protected override void ConnectToWorkspace(Workspace workspace)
-            => workspace.WorkspaceChanged += OnWorkspaceChanged;
+        {
+            _workspaceChangedDisposer = workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
+        }
 
         protected override void DisconnectFromWorkspace(Workspace workspace)
-            => workspace.WorkspaceChanged -= OnWorkspaceChanged;
+        {
+            _workspaceChangedDisposer?.Dispose();
+            _workspaceChangedDisposer = null;
+        }
 
-        private void OnWorkspaceChanged(object? sender, WorkspaceChangeEventArgs e)
+        private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
         {
             if (e.Kind == WorkspaceChangeKind.ProjectChanged)
             {

src/EditorFeatures/Core/Shared/Tagging/EventSources/TaggerEventSources.WorkspaceChangedEventSource.cs

@@ -15,6 +15,7 @@ internal partial class TaggerEventSources
     private sealed class WorkspaceChangedEventSource : AbstractWorkspaceTrackingTaggerEventSource
     {
         private readonly AsyncBatchingWorkQueue _asyncDelay;
+        private WorkspaceEventRegistration? _workspaceChangedDisposer;
 
         public WorkspaceChangedEventSource(
             ITextBuffer subjectBuffer,
@@ -36,17 +37,19 @@ public WorkspaceChangedEventSource(
 
         protected override void ConnectToWorkspace(Workspace workspace)
         {
-            workspace.WorkspaceChanged += OnWorkspaceChanged;
+            _workspaceChangedDisposer = workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
             this.RaiseChanged();
         }
 
         protected override void DisconnectFromWorkspace(Workspace workspace)
         {
-            workspace.WorkspaceChanged -= OnWorkspaceChanged;
+            _workspaceChangedDisposer?.Dispose();
+            _workspaceChangedDisposer = null;
+
             this.RaiseChanged();
         }
 
-        private void OnWorkspaceChanged(object? sender, WorkspaceChangeEventArgs eventArgs)
+        private void OnWorkspaceChanged(WorkspaceChangeEventArgs eventArgs)
             => _asyncDelay.AddWork();
     }
 }

src/EditorFeatures/Core/SolutionEvents/HostLegacySolutionEventsWorkspaceEventListener.cs

@@ -32,6 +32,8 @@ internal sealed partial class HostLegacySolutionEventsWorkspaceEventListener : I
     private readonly IThreadingContext _threadingContext;
     private readonly AsyncBatchingWorkQueue<WorkspaceChangeEventArgs> _eventQueue;
 
+    private WorkspaceEventRegistration? _workspaceChangedDisposer;
+
     [ImportingConstructor]
     [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
     public HostLegacySolutionEventsWorkspaceEventListener(
@@ -53,16 +55,19 @@ public void StartListening(Workspace workspace)
         // We only support this option to disable crawling in internal speedometer and ddrit perf runs to lower noise.
         // It is not exposed to the user.
         if (_globalOptions.GetOption(SolutionCrawlerRegistrationService.EnableSolutionCrawler))
-            workspace.WorkspaceChanged += OnWorkspaceChanged;
+            _workspaceChangedDisposer = workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
     }
 
     public void StopListening(Workspace workspace)
     {
         if (_globalOptions.GetOption(SolutionCrawlerRegistrationService.EnableSolutionCrawler))
-            workspace.WorkspaceChanged -= OnWorkspaceChanged;
+        {
+            _workspaceChangedDisposer?.Dispose();
+            _workspaceChangedDisposer = null;
+        }
     }
 
-    private void OnWorkspaceChanged(object? sender, WorkspaceChangeEventArgs e)
+    private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         // Legacy workspace events exist solely to let unit testing continue to work using their own fork of solution
         // crawler.  As such, they only need events for the project types they care about.  Specifically, that is only

src/Features/Core/Portable/Diagnostics/CodeAnalysisDiagnosticAnalyzerService.cs

@@ -11,8 +11,6 @@
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.Host.Mef;
-using Microsoft.CodeAnalysis.Shared.Utilities;
-using Microsoft.CodeAnalysis.Threading;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Diagnostics;
@@ -56,10 +54,12 @@ public CodeAnalysisDiagnosticAnalyzerService(
             _diagnosticAnalyzerService = diagnosticAnalyzerService;
             _workspace = workspace;
 
-            _workspace.WorkspaceChanged += OnWorkspaceChanged;
+            // Main thread as OnWorkspaceChanged's call to IDiagnosticAnalyzerService.RequestDiagnosticRefresh isn't clear on
+            // threading requirements
+            _ = workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged, WorkspaceEventOptions.RequiresMainThreadOptions);
         }
 
-        private void OnWorkspaceChanged(object? sender, WorkspaceChangeEventArgs e)
+        private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
         {
             switch (e.Kind)
             {

src/Features/Core/Portable/Workspace/CompileTimeSolutionProvider.cs

@@ -65,7 +65,7 @@ public IWorkspaceService CreateService(HostWorkspaceServices workspaceServices)
 
     public CompileTimeSolutionProvider(Workspace workspace)
     {
-        workspace.WorkspaceChanged += (s, e) =>
+        _ = workspace.RegisterWorkspaceChangedHandler((e) =>
         {
             if (e.Kind is WorkspaceChangeKind.SolutionCleared or WorkspaceChangeKind.SolutionRemoved)
             {
@@ -79,7 +79,7 @@ public CompileTimeSolutionProvider(Workspace workspace)
                     _lastCompileTimeSolution = null;
                 }
             }
-        };
+        });
     }
 
     private static bool IsRazorAnalyzerConfig(TextDocumentState documentState)

src/VisualStudio/Core/Def/DesignerAttribute/VisualStudioDesignerAttributeService.cs

@@ -60,6 +60,8 @@ internal sealed class VisualStudioDesignerAttributeService :
     // deliver them to VS in batches to prevent flooding the UI thread.
     private readonly AsyncBatchingWorkQueue<DesignerAttributeData> _projectSystemNotificationQueue;
 
+    private WorkspaceEventRegistration? _workspaceChangedDisposer;
+
     [ImportingConstructor]
     [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
     public VisualStudioDesignerAttributeService(
@@ -92,7 +94,7 @@ void IEventListener.StartListening(Workspace workspace)
         if (workspace != _workspace)
             return;
 
-        _workspace.WorkspaceChanged += OnWorkspaceChanged;
+        _workspaceChangedDisposer = workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
         _workQueue.AddWork(cancelExistingWork: true);
     }
 
@@ -101,10 +103,11 @@ void IEventListener.StopListening(Workspace workspace)
         if (workspace != _workspace)
             return;
 
-        _workspace.WorkspaceChanged -= OnWorkspaceChanged;
+        _workspaceChangedDisposer?.Dispose();
+        _workspaceChangedDisposer = null;
     }
 
-    private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
+    private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         _workQueue.AddWork(cancelExistingWork: true);
     }

src/VisualStudio/Core/Def/Library/ObjectBrowser/AbstractObjectBrowserLibraryManager.cs

@@ -41,6 +41,7 @@ internal abstract partial class AbstractObjectBrowserLibraryManager : AbstractLi
     private ObjectListItem _activeListItem;
     private AbstractListItemFactory _listItemFactory;
     private readonly object _classMemberGate = new();
+    private WorkspaceEventRegistration _workspaceChangedDisposer;
 
     protected AbstractObjectBrowserLibraryManager(
         string languageName,
@@ -53,7 +54,7 @@ protected AbstractObjectBrowserLibraryManager(
         _languageName = languageName;
 
         Workspace = workspace;
-        Workspace.WorkspaceChanged += OnWorkspaceChanged;
+        _workspaceChangedDisposer = Workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
 
         _libraryService = new Lazy<ILibraryService>(() => Workspace.Services.GetLanguageServices(_languageName).GetService<ILibraryService>());
     }
@@ -73,9 +74,12 @@ private AbstractListItemFactory GetListItemFactory()
     }
 
     public void Dispose()
-        => this.Workspace.WorkspaceChanged -= OnWorkspaceChanged;
+    {
+        _workspaceChangedDisposer?.Dispose();
+        _workspaceChangedDisposer = null;
+    }
 
-    private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
+    private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         switch (e.Kind)
         {

src/VisualStudio/Core/Def/Packaging/PackageInstallerServiceFactory.cs

@@ -232,7 +232,7 @@ protected override async Task EnableServiceAsync(CancellationToken cancellationT
         var packageSourceProvider = await GetPackageSourceProviderAsync().ConfigureAwait(false);
 
         // Start listening to additional events workspace changes.
-        Workspace.WorkspaceChanged += OnWorkspaceChanged;
+        _ = Workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
         packageSourceProvider.SourcesChanged += OnSourceProviderSourcesChanged;
 
         // Kick off an initial set of work that will analyze the entire solution.
@@ -421,7 +421,7 @@ await UpdateStatusBarAsync(
         }
     }
 
-    private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
+    private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         // ThisCanBeCalledOnAnyThread();
 

src/VisualStudio/Core/Def/Progression/GraphQueryManager.cs

@@ -50,7 +50,7 @@ internal GraphQueryManager(
         // indicating a change happened.  And when UpdateExistingQueriesAsync fires, it will just see that there are
         // no live queries and immediately return.  So it's just simple to do things this way instead of trying to 
         // have state management where we try to decide if we should listen or not.
-        _workspace.WorkspaceChanged += (_, _) => _updateQueue.AddWork();
+        _ = _workspace.RegisterWorkspaceChangedHandler((_) => _updateQueue.AddWork());
     }
 
     public async Task AddQueriesAsync(IGraphContext context, ImmutableArray<IGraphQuery> graphQueries, CancellationToken disposalToken)

src/VisualStudio/Core/Def/StackTraceExplorer/StackTraceExplorerViewModel.cs

@@ -5,8 +5,8 @@
 using System.Collections.ObjectModel;
 using System.Linq;
 using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.StackTraceExplorer;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
+using Microsoft.CodeAnalysis.StackTraceExplorer;
 using Microsoft.VisualStudio.LanguageServices.Utilities;
 using Microsoft.VisualStudio.Text.Classification;
 
@@ -53,7 +53,9 @@ public StackTraceExplorerViewModel(IThreadingContext threadingContext, Workspace
         _threadingContext = threadingContext;
         _workspace = workspace;
 
-        workspace.WorkspaceChanged += Workspace_WorkspaceChanged;
+        // Main thread dependency as Workspace_WorkspaceChanged modifies an ObservableCollection
+        _ = workspace.RegisterWorkspaceChangedHandler(Workspace_WorkspaceChanged, WorkspaceEventOptions.RequiresMainThreadOptions);
+
         _classificationTypeMap = classificationTypeMap;
         _formatMap = formatMap;
 
@@ -104,7 +106,7 @@ private void CallstackLines_CollectionChanged(object sender, System.Collections.
         NotifyPropertyChanged(nameof(IsInstructionTextVisible));
     }
 
-    private void Workspace_WorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
+    private void Workspace_WorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         if (e.Kind == WorkspaceChangeKind.SolutionChanged)
         {

src/VisualStudio/Core/Def/ValueTracking/ValueTrackingToolWindow.cs

@@ -3,11 +3,11 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
-using Microsoft.VisualStudio.Shell;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
-using System.Diagnostics.CodeAnalysis;
+using Microsoft.VisualStudio.Shell;
 
 namespace Microsoft.VisualStudio.LanguageServices.ValueTracking;
 
@@ -65,10 +65,10 @@ public void Initialize(ValueTrackingTreeViewModel viewModel, Workspace workspace
         _workspace = workspace;
         _threadingContext = threadingContext;
 
-        _workspace.WorkspaceChanged += OnWorkspaceChanged;
+        _ = _workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
     }
 
-    private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
+    private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
     {
         Contract.ThrowIfFalse(Initialized);
 

src/VisualStudio/Core/Def/Workspace/SourceGeneratedFileManager.cs

@@ -262,6 +262,7 @@ private sealed class OpenSourceGeneratedFile : IDisposable
         private VisualStudioInfoBar.InfoBarMessage? _currentInfoBarMessage;
 
         private InfoBarInfo? _infoToShow = null;
+        private WorkspaceEventRegistration? _workspaceChangedDisposer;
 
         public OpenSourceGeneratedFile(SourceGeneratedFileManager fileManager, ITextBuffer textBuffer, SourceGeneratedDocumentIdentity documentIdentity)
         {
@@ -284,7 +285,7 @@ public OpenSourceGeneratedFile(SourceGeneratedFileManager fileManager, ITextBuff
                 readOnlyRegionEdit.Apply();
             }
 
-            this.Workspace.WorkspaceChanged += OnWorkspaceChanged;
+            _workspaceChangedDisposer = this.Workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChanged);
 
             _batchingWorkQueue = new AsyncBatchingWorkQueue(
                 TimeSpan.FromSeconds(1),
@@ -311,7 +312,8 @@ public void Dispose()
         {
             _fileManager._threadingContext.ThrowIfNotOnUIThread();
 
-            this.Workspace.WorkspaceChanged -= OnWorkspaceChanged;
+            _workspaceChangedDisposer?.Dispose();
+            _workspaceChangedDisposer = null;
 
             // Disconnect the buffer from the workspace before making it eligible for edits
             DisconnectFromWorkspaceIfOpen();
@@ -422,7 +424,7 @@ public async ValueTask RefreshFileAsync(CancellationToken cancellationToken)
             await EnsureWindowFrameInfoBarUpdatedAsync(cancellationToken).ConfigureAwait(true);
         }
 
-        private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
+        private void OnWorkspaceChanged(WorkspaceChangeEventArgs e)
         {
             var projectId = _documentIdentity.DocumentId.ProjectId;