Use ConfigureAwait(true) when in a blocking JTF run call (#79456)

Author: CyrusNajmabadi

src/VisualStudio/Core/Def/Extensions/VsTextSpanExtensions.cs

@@ -5,6 +5,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Editor.Shared.Extensions;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
 using Microsoft.VisualStudio.LanguageServices.Implementation.Venus;
 using VsTextSpan = Microsoft.VisualStudio.TextManager.Interop.TextSpan;
@@ -24,6 +25,24 @@ internal static class VsTextSpanExtensions
             return null;
 
         await threadingContext.JoinableTaskFactory.SwitchToMainThreadAsync(cancellationToken);
+        return MapSpanFromSecondaryBufferToPrimaryBuffer(
+            spanInSecondaryBuffer, threadingContext, documentId, containedDocument);
+    }
+
+    /// <summary>
+    /// Only call this from the UI thread.  See <see cref="MapSpanFromSecondaryBufferToPrimaryBufferAsync"/> for the async version.
+    /// </summary>
+    public static VsTextSpan? MapSpanFromSecondaryBufferToPrimaryBuffer(
+        this VsTextSpan spanInSecondaryBuffer,
+        IThreadingContext threadingContext,
+        DocumentId documentId,
+        ContainedDocument? containedDocument = null)
+    {
+        threadingContext.ThrowIfNotOnUIThread();
+
+        containedDocument ??= ContainedDocument.TryGetContainedDocument(documentId);
+        if (containedDocument == null)
+            return null;
         var bufferCoordinator = containedDocument.BufferCoordinator;
 
         var primary = new VsTextSpan[1];

src/VisualStudio/Core/Def/LanguageService/AbstractLanguageService`2.VsLanguageDebugInfo.cs

@@ -177,8 +177,13 @@ public int ResolveName(string? pszName, uint dwFlags, out IVsEnumDebugName? ppNa
                 return VSConstants.S_FALSE;
             }
 
+            // NOTE(cyrusn): We have to wait here because the debuggers' ResolveName
+            // call is synchronous.  In the future it would be nice to make it async.
             ppNames = this.ThreadingContext.JoinableTaskFactory.Run(async () =>
             {
+                // We're in a blocking JTF run.  So ConfigureAwait(true) all calls to ensure we're coming back
+                // and using the blocked thread whenever possible.
+
                 using (Logger.LogBlock(FunctionId.Debugging_VsLanguageDebugInfo_ResolveName, CancellationToken.None))
                 {
                     using var waitContext = _uiThreadOperationExecutor.BeginExecute(
@@ -192,14 +197,11 @@ public int ResolveName(string? pszName, uint dwFlags, out IVsEnumDebugName? ppNa
                     {
                         var solution = _languageService.Workspace.CurrentSolution;
 
-                        // NOTE(cyrusn): We have to wait here because the debuggers' ResolveName
-                        // call is synchronous.  In the future it would be nice to make it async.
                         if (_breakpointService != null)
                         {
                             var breakpoints = await _breakpointService.ResolveBreakpointsAsync(
-                                solution, pszName, cancellationToken).ConfigureAwait(false);
-                            var debugNames = await breakpoints.SelectAsArrayAsync(
-                                bp => CreateDebugNameAsync(bp, cancellationToken)).ConfigureAwait(true);
+                                solution, pszName, cancellationToken).ConfigureAwait(true);
+                            var debugNames = breakpoints.SelectAsArray(bp => CreateDebugName(bp, cancellationToken));
 
                             return new VsEnumDebugName(debugNames);
                         }
@@ -210,23 +212,28 @@ public int ResolveName(string? pszName, uint dwFlags, out IVsEnumDebugName? ppNa
             });
 
             return ppNames != null ? VSConstants.S_OK : VSConstants.E_NOTIMPL;
-        }
 
-        private async ValueTask<IVsDebugName> CreateDebugNameAsync(
-            BreakpointResolutionResult breakpoint, CancellationToken cancellationToken)
-        {
-            var document = breakpoint.Document;
-            var filePath = _languageService.Workspace.GetFilePath(document.Id);
-            var text = await document.GetValueTextAsync(cancellationToken).ConfigureAwait(false);
-            var span = text.GetVsTextSpanForSpan(breakpoint.TextSpan);
-            // If we're inside an Venus code nugget, we need to map the span to the surface buffer.
-            // Otherwise, we'll just use the original span.
-            var mappedSpan = await span.MapSpanFromSecondaryBufferToPrimaryBufferAsync(
-                this.ThreadingContext, document.Id, cancellationToken).ConfigureAwait(true);
-            if (mappedSpan != null)
-                span = mappedSpan.Value;
-
-            return new VsDebugName(breakpoint.LocationNameOpt, filePath!, span);
+            IVsDebugName CreateDebugName(
+                BreakpointResolutionResult breakpoint, CancellationToken cancellationToken)
+            {
+                // We're in a blocking jtf run.  So CA(true) all calls to ensure we're coming bac
+                // and using the blocked thread whenever possible.
+
+                var document = breakpoint.Document;
+                var filePath = _languageService.Workspace.GetFilePath(document.Id);
+
+                // We're (unfortunately) blocking the UI thread here.  So avoid async io as we actually
+                // awant the IO to complete as quickly as possible, on this thread if necessary.
+                var text = document.GetTextSynchronously(cancellationToken);
+                var span = text.GetVsTextSpanForSpan(breakpoint.TextSpan);
+                // If we're inside an Venus code nugget, we need to map the span to the surface buffer.
+                // Otherwise, we'll just use the original span.
+                var mappedSpan = span.MapSpanFromSecondaryBufferToPrimaryBuffer(this.ThreadingContext, document.Id);
+                if (mappedSpan != null)
+                    span = mappedSpan.Value;
+
+                return new VsDebugName(breakpoint.LocationNameOpt, filePath!, span);
+            }
         }
 
         public int ValidateBreakpointLocation(IVsTextBuffer pBuffer, int iLine, int iCol, VsTextSpan[] pCodeSpan)