From 8aa4e0ac2bdf1f7b185753eca0f1f7b4bc5c05c1 Mon Sep 17 00:00:00 2001
From: David Wengier <david.wengier@microsoft.com>
Date: Mon, 21 Mar 2022 09:09:21 +1100
Subject: [PATCH] Don't block on clearing the output window on the UI thread
 when generating a file (#60281)

---
 .../IPdbSourceDocumentLogger.cs                |  2 +-
 ...urceDocumentMetadataAsSourceFileProvider.cs |  9 ++-------
 .../PdbSourceDocumentOutputWindowLogger.cs     | 18 ++++++++++--------
 3 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/src/Features/Core/Portable/PdbSourceDocument/IPdbSourceDocumentLogger.cs b/src/Features/Core/Portable/PdbSourceDocument/IPdbSourceDocumentLogger.cs
index f29569eb36f25..03cdd54f3baee 100644
--- a/src/Features/Core/Portable/PdbSourceDocument/IPdbSourceDocumentLogger.cs
+++ b/src/Features/Core/Portable/PdbSourceDocument/IPdbSourceDocumentLogger.cs
@@ -12,7 +12,7 @@ namespace Microsoft.CodeAnalysis.PdbSourceDocument
     /// </summary>
     internal interface IPdbSourceDocumentLogger
     {
-        Task ClearAsync();
+        void Clear();
         void Log(string message);
     }
 
diff --git a/src/Features/Core/Portable/PdbSourceDocument/PdbSourceDocumentMetadataAsSourceFileProvider.cs b/src/Features/Core/Portable/PdbSourceDocument/PdbSourceDocumentMetadataAsSourceFileProvider.cs
index fee7d42220e2c..a359f330eea38 100644
--- a/src/Features/Core/Portable/PdbSourceDocument/PdbSourceDocumentMetadataAsSourceFileProvider.cs
+++ b/src/Features/Core/Portable/PdbSourceDocument/PdbSourceDocumentMetadataAsSourceFileProvider.cs
@@ -60,13 +60,8 @@ internal sealed class PdbSourceDocumentMetadataAsSourceFileProvider : IMetadataA
             var assemblyName = symbol.ContainingAssembly.Identity.Name;
             var assemblyVersion = symbol.ContainingAssembly.Identity.Version.ToString();
 
-            if (_logger is not null)
-            {
-                // We block to clear the log from the previous operation, so things don't get confusing
-                // if the log messages are delayed
-                await _logger.ClearAsync().ConfigureAwait(false);
-            }
-
+            // Clear the log so messages from the previously generated file don't confuse the user
+            _logger?.Clear();
             _logger?.Log(FeaturesResources.Navigating_to_symbol_0_from_1, symbol, assemblyName);
 
             var compilation = await project.GetRequiredCompilationAsync(cancellationToken).ConfigureAwait(false);
diff --git a/src/VisualStudio/Core/Def/PdbSourceDocument/PdbSourceDocumentOutputWindowLogger.cs b/src/VisualStudio/Core/Def/PdbSourceDocument/PdbSourceDocumentOutputWindowLogger.cs
index b5e020e435942..f690746ef9ce5 100644
--- a/src/VisualStudio/Core/Def/PdbSourceDocument/PdbSourceDocumentOutputWindowLogger.cs
+++ b/src/VisualStudio/Core/Def/PdbSourceDocument/PdbSourceDocumentOutputWindowLogger.cs
@@ -27,7 +27,7 @@ internal sealed class PdbSourceDocumentOutputWindowLogger : IPdbSourceDocumentLo
         private IVsOutputWindowPane? _outputPane;
 
         private readonly IThreadingContext _threadingContext;
-        private readonly AsyncBatchingWorkQueue<string> _logItemsQueue;
+        private readonly AsyncBatchingWorkQueue<string?> _logItemsQueue;
         private readonly IServiceProvider _serviceProvider;
 
         private readonly CancellationTokenSource _cancellationTokenSource = new();
@@ -41,14 +41,14 @@ public PdbSourceDocumentOutputWindowLogger(SVsServiceProvider serviceProvider, I
 
             var asyncListener = listenerProvider.GetListener(nameof(PdbSourceDocumentOutputWindowLogger));
 
-            _logItemsQueue = new AsyncBatchingWorkQueue<string>(
+            _logItemsQueue = new AsyncBatchingWorkQueue<string?>(
                 DelayTimeSpan.NearImmediate,
                 ProcessLogMessagesAsync,
                 asyncListener,
                 _cancellationTokenSource.Token);
         }
 
-        private async ValueTask ProcessLogMessagesAsync(ImmutableArray<string> messages, CancellationToken cancellationToken)
+        private async ValueTask ProcessLogMessagesAsync(ImmutableArray<string?> messages, CancellationToken cancellationToken)
         {
             await _threadingContext.JoinableTaskFactory.SwitchToMainThreadAsync(cancellationToken);
 
@@ -60,7 +60,11 @@ private async ValueTask ProcessLogMessagesAsync(ImmutableArray<string> messages,
                     return;
                 }
 
-                if (pane is IVsOutputWindowPaneNoPump noPumpPane)
+                if (message is null)
+                {
+                    pane.Clear();
+                }
+                else if (pane is IVsOutputWindowPaneNoPump noPumpPane)
                 {
                     noPumpPane.OutputStringNoPump(message + Environment.NewLine);
                 }
@@ -71,11 +75,9 @@ private async ValueTask ProcessLogMessagesAsync(ImmutableArray<string> messages,
             }
         }
 
-        public async Task ClearAsync()
+        public void Clear()
         {
-            await _threadingContext.JoinableTaskFactory.SwitchToMainThreadAsync();
-
-            GetPane()?.Clear();
+            _logItemsQueue.AddWork((string?)null);
         }
 
         public void Log(string value)