Another attempt to move MiscellaneousFilesWorkspace to a bg thread

src/VisualStudio/Core/Def/LanguageService/AbstractPackage`2.cs

@@ -39,6 +39,7 @@ protected override void RegisterInitializeAsyncWork(PackageLoadTasks packageInit
         base.RegisterInitializeAsyncWork(packageInitializationTasks);
 
         packageInitializationTasks.AddTask(isMainThreadTask: true, task: PackageInitializationMainThreadAsync);
+        packageInitializationTasks.AddTask(isMainThreadTask: false, task: PackageInitializationBackgroundThreadAsync);
     }
 
     private async Task PackageInitializationMainThreadAsync(PackageLoadTasks packageInitializationTasks, CancellationToken cancellationToken)
@@ -58,35 +59,33 @@ private async Task PackageInitializationMainThreadAsync(PackageLoadTasks package
             RegisterEditorFactory(editorFactory);
         }
 
-        // Misc workspace has to be up and running by the time our package is usable so that it can track running
-        // doc events and appropriately map files to/from it and other relevant workspaces (like the
-        // metadata-as-source workspace).
-        var miscellaneousFilesWorkspace = this.ComponentModel.GetService<MiscellaneousFilesWorkspace>();
-
         // awaiting an IVsTask guarantees to return on the captured context
         await shell.LoadPackageAsync(Guids.RoslynPackageId);
+    }
 
-        packageInitializationTasks.AddTask(
-             isMainThreadTask: false,
-             task: (PackageLoadTasks packageInitializationTasks, CancellationToken cancellationToken) =>
-             {
-                 RegisterLanguageService(typeof(TLanguageService), async cancellationToken =>
-                 {
-                     // Ensure we're on the BG when creating the language service.
-                     await TaskScheduler.Default;
+    private Task PackageInitializationBackgroundThreadAsync(PackageLoadTasks packageInitializationTasks, CancellationToken cancellationToken)
+    {
+        RegisterLanguageService(typeof(TLanguageService), async cancellationToken =>
+        {
+            // Ensure we're on the BG when creating the language service.
+            await TaskScheduler.Default;
+
+            // Create the language service, tell it to set itself up, then store it in a field
+            // so we can notify it that it's time to clean up.
+            _languageService = CreateLanguageService();
+            await _languageService.SetupAsync(cancellationToken).ConfigureAwait(false);
 
-                     // Create the language service, tell it to set itself up, then store it in a field
-                     // so we can notify it that it's time to clean up.
-                     _languageService = CreateLanguageService();
-                     await _languageService.SetupAsync(cancellationToken).ConfigureAwait(false);
+            return _languageService.ComAggregate!;
+        });
 
-                     return _languageService.ComAggregate!;
-                 });
+        // Misc workspace has to be up and running by the time our package is usable so that it can track running
+        // doc events and appropriately map files to/from it and other relevant workspaces (like the
+        // metadata-as-source workspace).
+        var miscellaneousFilesWorkspace = this.ComponentModel.GetService<MiscellaneousFilesWorkspace>();
 
-                 RegisterMiscellaneousFilesWorkspaceInformation(miscellaneousFilesWorkspace);
+        RegisterMiscellaneousFilesWorkspaceInformation(miscellaneousFilesWorkspace);
 
-                 return Task.CompletedTask;
-             });
+        return Task.CompletedTask;
     }
 
     protected override void RegisterOnAfterPackageLoadedAsyncWork(PackageLoadTasks afterPackageLoadedTasks)

src/VisualStudio/Core/Def/ProjectSystem/MiscellaneousFilesWorkspace.cs

@@ -31,7 +31,7 @@ internal sealed partial class MiscellaneousFilesWorkspace : Workspace, IOpenText
     private readonly IThreadingContext _threadingContext;
     private readonly IVsService<IVsTextManager> _textManagerService;
     private readonly OpenTextBufferProvider _openTextBufferProvider;
-    private readonly IMetadataAsSourceFileService _fileTrackingMetadataAsSourceService;
+    private readonly Lazy<IMetadataAsSourceFileService> _fileTrackingMetadataAsSourceService;
 
     private readonly ConcurrentDictionary<Guid, LanguageInformation> _languageInformationByLanguageGuid = [];
 
@@ -47,24 +47,24 @@ internal sealed partial class MiscellaneousFilesWorkspace : Workspace, IOpenText
     /// </summary>
     private readonly Dictionary<string, (ProjectId projectId, SourceTextContainer textContainer)> _monikersToProjectIdAndContainer = [];
 
-    private readonly ImmutableArray<MetadataReference> _metadataReferences;
+    private readonly Lazy<ImmutableArray<MetadataReference>> _metadataReferences;
 
     [ImportingConstructor]
     [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
     public MiscellaneousFilesWorkspace(
         IThreadingContext threadingContext,
         IVsService<SVsTextManager, IVsTextManager> textManagerService,
         OpenTextBufferProvider openTextBufferProvider,
-        IMetadataAsSourceFileService fileTrackingMetadataAsSourceService,
-        VisualStudioWorkspace visualStudioWorkspace)
-        : base(visualStudioWorkspace.Services.HostServices, WorkspaceKind.MiscellaneousFiles)
+        Lazy<IMetadataAsSourceFileService> fileTrackingMetadataAsSourceService,
+        Composition.ExportProvider exportProvider)
+        : base(VisualStudioMefHostServices.Create(exportProvider), WorkspaceKind.MiscellaneousFiles)
     {
         _threadingContext = threadingContext;
         _textManagerService = textManagerService;
         _openTextBufferProvider = openTextBufferProvider;
         _fileTrackingMetadataAsSourceService = fileTrackingMetadataAsSourceService;
 
-        _metadataReferences = [.. CreateMetadataReferences()];
+        _metadataReferences = new(() => [.. CreateMetadataReferences()]);
 
         _openTextBufferProvider.AddListener(this);
     }
@@ -122,6 +122,10 @@ public void RegisterLanguage(Guid languageGuid, string languageName, string scri
 
     private IEnumerable<MetadataReference> CreateMetadataReferences()
     {
+        // VisualStudioMetadataReferenceManager construction requires the main thread
+        // TODO: Determine if main thread affinity can be removed: https://github.com/dotnet/roslyn/issues/77791
+        _threadingContext.ThrowIfNotOnUIThread();
+
         var manager = this.Services.GetService<VisualStudioMetadataReferenceManager>();
         var searchPaths = VisualStudioMetadataReferenceManager.GetReferencePaths();
 
@@ -261,7 +265,7 @@ private void AttachToDocument(string moniker, ITextBuffer textBuffer)
     {
         _threadingContext.ThrowIfNotOnUIThread();
 
-        if (_fileTrackingMetadataAsSourceService.TryAddDocumentToWorkspace(moniker, textBuffer.AsTextContainer(), out var _))
+        if (_fileTrackingMetadataAsSourceService.Value.TryAddDocumentToWorkspace(moniker, textBuffer.AsTextContainer(), out var _))
         {
             // We already added it, so we will keep it excluded from the misc files workspace
             return;
@@ -282,20 +286,24 @@ private void AttachToDocument(string moniker, ITextBuffer textBuffer)
     /// </summary>
     private ProjectInfo CreateProjectInfoForDocument(string filePath)
     {
+        // Potential calculation of _metadataReferences requires being on the main thread
+        // TODO: Determine if main thread affinity can be removed: https://github.com/dotnet/roslyn/issues/77791
+        _threadingContext.ThrowIfNotOnUIThread();
+
         // This should always succeed since we only got here if we already confirmed the moniker is acceptable
         var languageInformation = TryGetLanguageInformation(filePath);
         Contract.ThrowIfNull(languageInformation);
 
         var checksumAlgorithm = SourceHashAlgorithms.Default;
         var fileLoader = new WorkspaceFileTextLoader(Services.SolutionServices, filePath, defaultEncoding: null);
         return MiscellaneousFileUtilities.CreateMiscellaneousProjectInfoForDocument(
-            this, filePath, fileLoader, languageInformation, checksumAlgorithm, Services.SolutionServices, _metadataReferences);
+            this, filePath, fileLoader, languageInformation, checksumAlgorithm, Services.SolutionServices, _metadataReferences.Value);
     }
 
     private void DetachFromDocument(string moniker)
     {
         _threadingContext.ThrowIfNotOnUIThread();
-        if (_fileTrackingMetadataAsSourceService.TryRemoveDocumentFromWorkspace(moniker))
+        if (_fileTrackingMetadataAsSourceService.Value.TryRemoveDocumentFromWorkspace(moniker))
         {
             return;
         }