Use immutable arrays.

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

@@ -313,7 +313,7 @@ private void AddFilteredInfos(ImmutableArray<DesignerAttributeData> data, ArrayB
         /// <summary>
         /// Callback from the OOP service back into us.
         /// </summary>
-        public Task ReportDesignerAttributeDataAsync(IList<DesignerAttributeData> data, CancellationToken cancellationToken)
+        public Task ReportDesignerAttributeDataAsync(ImmutableArray<DesignerAttributeData> data, CancellationToken cancellationToken)
         {
             Contract.ThrowIfNull(_workQueue);
             _workQueue.AddWork(data);

src/VisualStudio/Core/Def/Implementation/TodoComments/VisualStudioTodoCommentsService.cs

@@ -181,7 +181,7 @@ public ImmutableArray<TodoCommentData> GetTodoItems(Workspace workspace, Documen
         /// <summary>
         /// Callback from the OOP service back into us.
         /// </summary>
-        public Task ReportTodoCommentDataAsync(DocumentId documentId, List<TodoCommentData> infos, CancellationToken cancellationToken)
+        public Task ReportTodoCommentDataAsync(DocumentId documentId, ImmutableArray<TodoCommentData> infos, CancellationToken cancellationToken)
         {
             Contract.ThrowIfNull(_workQueue);
             _workQueue.AddWork(new DocumentAndComments(documentId, infos.ToImmutableArray()));

src/Workspaces/Core/Portable/DesignerAttribute/IDesignerAttributeListener.cs

@@ -4,7 +4,7 @@
 
 #nullable enable
 
-using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -19,6 +19,6 @@ namespace Microsoft.CodeAnalysis.DesignerAttribute
     internal interface IDesignerAttributeListener
     {
         Task OnProjectRemovedAsync(ProjectId projectId, CancellationToken cancellationToken);
-        Task ReportDesignerAttributeDataAsync(IList<DesignerAttributeData> data, CancellationToken cancellationToken);
+        Task ReportDesignerAttributeDataAsync(ImmutableArray<DesignerAttributeData> data, CancellationToken cancellationToken);
     }
 }

src/Workspaces/Core/Portable/TodoComments/ITodoCommentsListener.cs

@@ -4,7 +4,7 @@
 
 #nullable enable
 
-using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -17,6 +17,6 @@ namespace Microsoft.CodeAnalysis.TodoComments
     internal interface ITodoCommentsListener
     {
         Task OnDocumentRemovedAsync(DocumentId documentId, CancellationToken cancellationToken);
-        Task ReportTodoCommentDataAsync(DocumentId documentId, List<TodoCommentData> data, CancellationToken cancellationToken);
+        Task ReportTodoCommentDataAsync(DocumentId documentId, ImmutableArray<TodoCommentData> data, CancellationToken cancellationToken);
     }
 }

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Utilities/AsyncBatchingWorkQueue.cs

@@ -90,20 +90,38 @@ public void AddWork(IEnumerable<TItem> items)
             {
                 // add our work to the set we'll process in the next batch.
                 _nextBatch.AddRange(items);
+                TryKickOffNextBatchTask();
+            }
+        }
+
+        public void AddWork(ImmutableArray<TItem> items)
+        {
+            // Don't do any more work if we've been asked to shutdown.
+            if (_cancellationToken.IsCancellationRequested)
+                return;
+
+            lock (_gate)
+            {
+                // add our work to the set we'll process in the next batch.
+                _nextBatch.AddRange(items);
+                TryKickOffNextBatchTask();
+            }
+        }
 
-                if (!_taskInFlight)
-                {
-                    // No in-flight task.  Kick one off to process these messages a second from now.
-                    // We always attach the task to the previous one so that notifications to the ui
-                    // follow the same order as the notification the OOP server sent to us.
-                    _updateTask = _updateTask.ContinueWithAfterDelayFromAsync(
-                        _ => ProcessNextBatchAsync(_cancellationToken),
-                        _cancellationToken,
-                        (int)_delay.TotalMilliseconds,
-                        TaskContinuationOptions.RunContinuationsAsynchronously,
-                        TaskScheduler.Default);
-                    _taskInFlight = true;
-                }
+        private void TryKickOffNextBatchTask()
+        {
+            if (!_taskInFlight)
+            {
+                // No in-flight task.  Kick one off to process these messages a second from now.
+                // We always attach the task to the previous one so that notifications to the ui
+                // follow the same order as the notification the OOP server sent to us.
+                _updateTask = _updateTask.ContinueWithAfterDelayFromAsync(
+                    _ => ProcessNextBatchAsync(_cancellationToken),
+                    _cancellationToken,
+                    (int)_delay.TotalMilliseconds,
+                    TaskContinuationOptions.RunContinuationsAsynchronously,
+                    TaskScheduler.Default);
+                _taskInFlight = true;
             }
         }