From ad518ac6787ab8265adcd1a4eddc70c390590ca6 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Wed, 3 Aug 2022 15:00:42 +0300
Subject: [PATCH 1/2] Add backpressure for sending batches to the render thread

---
 .../Rendering/Composition/CompositingRenderer.cs      |  2 +-
 src/Avalonia.Base/Rendering/Composition/Compositor.cs | 11 ++++++++++-
 .../Rendering/Composition/Server/ServerCompositor.cs  |  3 +--
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs b/src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs
index db773bc43c..9aa3c25425 100644
--- a/src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs
+++ b/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/>
diff --git a/src/Avalonia.Base/Rendering/Composition/Compositor.cs b/src/Avalonia.Base/Rendering/Composition/Compositor.cs
index 45212d0f36..f812acc016 100644
--- a/src/Avalonia.Base/Rendering/Composition/Compositor.cs
+++ b/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 +140,13 @@ 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(_ => Dispatcher.UIThread.Post(action, DispatcherPriority.Composition));
+        }
     }
 }
diff --git a/src/Avalonia.Base/Rendering/Composition/Server/ServerCompositor.cs b/src/Avalonia.Base/Rendering/Composition/Server/ServerCompositor.cs
index 621bc84f4a..bfc2b2d626 100644
--- a/src/Avalonia.Base/Rendering/Composition/Server/ServerCompositor.cs
+++ b/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)

From 0d472a100b6fc191d69675512028c4e770045081 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Wed, 3 Aug 2022 15:57:13 +0300
Subject: [PATCH 2/2] Use static callback for ContinueWith

---
 src/Avalonia.Base/Rendering/Composition/Compositor.cs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Rendering/Composition/Compositor.cs b/src/Avalonia.Base/Rendering/Composition/Compositor.cs
index f812acc016..10360f7874 100644
--- a/src/Avalonia.Base/Rendering/Composition/Compositor.cs
+++ b/src/Avalonia.Base/Rendering/Composition/Compositor.cs
@@ -146,7 +146,9 @@ namespace Avalonia.Rendering.Composition
             if (_lastBatchCompleted == null || _lastBatchCompleted.IsCompleted)
                 Dispatcher.UIThread.Post(action, DispatcherPriority.Composition);
             else
-                _lastBatchCompleted.ContinueWith(_ => Dispatcher.UIThread.Post(action, DispatcherPriority.Composition));
+                _lastBatchCompleted.ContinueWith(
+                    static (_, state) => Dispatcher.UIThread.Post((Action)state!, DispatcherPriority.Composition),
+                    action);
         }
     }
 }