Merge pull request #8658 from AvaloniaUI/fixes/invalidate-visual-backpressure

Add backpressure for sending batches to the render thread

src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs

@@ -71,7 +71,7 @@ public class CompositingRenderer : IRendererWithCompositor
         if(_queuedUpdate)
             return;
         _queuedUpdate = true;
-        Dispatcher.UIThread.Post(_update, DispatcherPriority.Composition);
+        _compositor.InvokeWhenReadyForNextCommit(_update);
     }
     
     /// <inheritdoc/>

src/Avalonia.Base/Rendering/Composition/Compositor.cs

@@ -33,6 +33,7 @@ namespace Avalonia.Rendering.Composition
         internal IEasing DefaultEasing { get; }
         private List<Action>? _invokeOnNextCommit;
         private readonly Stack<List<Action>> _invokeListPool = new();
+        private Task? _lastBatchCompleted;
 
         /// <summary>
         /// Creates a new compositor on a specified render loop that would use a particular GPU
@@ -86,7 +87,7 @@ namespace Avalonia.Rendering.Composition
             if (_invokeOnNextCommit != null) 
                 ScheduleCommitCallbacks(batch.Completed);
             
-            return batch.Completed;
+            return _lastBatchCompleted = batch.Completed;
         }
 
         async void ScheduleCommitCallbacks(Task task)
@@ -139,5 +140,15 @@ namespace Avalonia.Rendering.Composition
             _invokeOnNextCommit ??= _invokeListPool.Count > 0 ? _invokeListPool.Pop() : new();
             _invokeOnNextCommit.Add(action);
         }
+
+        public void InvokeWhenReadyForNextCommit(Action action)
+        {
+            if (_lastBatchCompleted == null || _lastBatchCompleted.IsCompleted)
+                Dispatcher.UIThread.Post(action, DispatcherPriority.Composition);
+            else
+                _lastBatchCompleted.ContinueWith(
+                    static (_, state) => Dispatcher.UIThread.Post((Action)state!, DispatcherPriority.Composition),
+                    action);
+        }
     }
 }

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositor.cs

@@ -108,6 +108,7 @@ namespace Avalonia.Rendering.Composition.Server
         private void RenderCore()
         {
             ApplyPendingBatches();
+            CompletePendingBatches();
             
             foreach(var animation in _activeAnimations)
                 _animationsToUpdate.Add(animation);
@@ -119,8 +120,6 @@ namespace Avalonia.Rendering.Composition.Server
             
             foreach (var t in _activeTargets)
                 t.Render();
-            
-            CompletePendingBatches();
         }
 
         public void AddCompositionTarget(ServerCompositionTarget target)