Merge pull request #45477 from sharwell/touch-document-lite

Reduce memory required for document change processing queues

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

@@ -94,10 +94,7 @@ private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
                     var oldDocument = e.OldSolution.GetDocument(e.DocumentId);
                     var newDocument = e.NewSolution.GetDocument(e.DocumentId);
 
-                    // make sure we do this in background thread. we don't care about ordering of events
-                    // we just need to refresh OB at some point if it ever needs to be updated
-                    // link to the bug tracking root cause  - https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=169649&_a=edit
-                    Task.Run(() => DocumentChangedAsync(oldDocument, newDocument));
+                    UpdateDocument(oldDocument, newDocument);
                     break;
 
                 case WorkspaceChangeKind.ProjectAdded:
@@ -117,17 +114,21 @@ private void OnWorkspaceChanged(object sender, WorkspaceChangeEventArgs e)
             }
         }
 
-        private async Task DocumentChangedAsync(Document oldDocument, Document newDocument)
+        private void UpdateDocument(Document oldDocument, Document newDocument)
         {
             try
             {
-                var oldTextVersion = await oldDocument.GetTextVersionAsync(CancellationToken.None).ConfigureAwait(false);
-                var newTextVersion = await newDocument.GetTextVersionAsync(CancellationToken.None).ConfigureAwait(false);
-
-                if (oldTextVersion != newTextVersion)
+                // If the versions are the same, avoid updating the object browser. However, avoid
+                // loading the document to determine the version because it can cause extreme memory
+                // pressure during batch changes.
+                if (oldDocument.TryGetTextVersion(out var oldTextVersion)
+                    && newDocument.TryGetTextVersion(out var newTextVersion)
+                    && oldTextVersion == newTextVersion)
                 {
-                    UpdateClassAndMemberVersions();
+                    return;
                 }
+
+                UpdateClassAndMemberVersions();
             }
             catch (Exception e) when (FatalError.Report(e))
             {

src/Workspaces/Core/Portable/Workspace/Solution/RecoverableTextAndVersion.cs

@@ -67,6 +67,10 @@ public bool TryGetTextVersion(out VersionStamp version)
                 {
                     version = textAndVersion.Version;
                 }
+                else if (_initialSource is ITextVersionable textVersionable)
+                {
+                    return textVersionable.TryGetTextVersion(out version);
+                }
             }
 
             return version != default;

src/Workspaces/Core/Portable/Workspace/Solution/TextDocumentState.cs

@@ -97,7 +97,19 @@ protected static ValueSource<TextAndVersion> CreateStrongText(TextLoader loader,
         }
 
         protected static ValueSource<TextAndVersion> CreateRecoverableText(TextAndVersion text, SolutionServices services)
-            => new RecoverableTextAndVersion(CreateStrongText(text), services.TemporaryStorage);
+        {
+            var result = new RecoverableTextAndVersion(CreateStrongText(text), services.TemporaryStorage);
+
+            // This RecoverableTextAndVersion is created directly from a TextAndVersion instance. In its initial state,
+            // the RecoverableTextAndVersion keeps a strong reference to the initial TextAndVersion, and only
+            // transitions to a weak reference backed by temporary storage after the first time GetValue (or
+            // GetValueAsync) is called. Since we know we are creating a RecoverableTextAndVersion for the purpose of
+            // avoiding problematic address space overhead, we call GetValue immediately to force the object to weakly
+            // hold its data from the start.
+            result.GetValue();
+
+            return result;
+        }
 
         protected static ValueSource<TextAndVersion> CreateRecoverableText(TextLoader loader, DocumentId documentId, SolutionServices services)
         {