Added some threading checks

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

@@ -21,16 +21,45 @@ public abstract class CompositionCustomVisualHandler
     
     public abstract void OnRender(ImmediateDrawingContext drawingContext);
 
-    protected Vector2 EffectiveSize => _host?.Size ?? default;
+    void VerifyAccess()
+    {
+        if (_host == null)
+            throw new InvalidOperationException("Object is not yet attached to the compositor");
+        _host.Compositor.VerifyAccess();
+    }
+
+    protected Vector2 EffectiveSize
+    {
+        get
+        {
+            VerifyAccess();
+            return _host!.Size;
+        }
+    }
+
+    protected TimeSpan CompositionNow
+    {
+        get
+        {
+            VerifyAccess();
+            return _host!.Compositor.ServerNow;
+        }
+    }
 
-    protected TimeSpan CompositionNow => _host?.Compositor.ServerNow ?? default;
-    
     public virtual Rect GetRenderBounds() =>
         new(0, 0, EffectiveSize.X, EffectiveSize.Y);
 
     internal void Attach(ServerCompositionCustomVisual visual) => _host = visual;
 
-    protected void Invalidate() => _host?.HandlerInvalidate();
+    protected void Invalidate()
+    {
+        VerifyAccess();
+        _host!.HandlerInvalidate();
+    }
 
-    protected void RegisterForNextAnimationFrameUpdate() => _host?.HandlerRegisterForNextAnimationFrameUpdate();
+    protected void RegisterForNextAnimationFrameUpdate()
+    {
+        VerifyAccess();
+        _host!.HandlerRegisterForNextAnimationFrameUpdate();
+    }
 }

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

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Threading;
 using Avalonia.Logging;
 using Avalonia.Platform;
 using Avalonia.Rendering.Composition.Animations;
@@ -31,6 +32,7 @@ namespace Avalonia.Rendering.Composition.Server
         internal BatchStreamObjectPool<object?> BatchObjectPool;
         internal BatchStreamMemoryPool BatchMemoryPool;
         private object _lock = new object();
+        private Thread? _safeThread;
         public PlatformRenderInterfaceContextManager RenderInterface { get; }
         internal static readonly object RenderThreadJobsStartMarker = new();
         internal static readonly object RenderThreadJobsEndMarker = new();
@@ -129,7 +131,15 @@ namespace Avalonia.Rendering.Composition.Server
         {
             lock (_lock)
             {
-                RenderCore();
+                try
+                {
+                    _safeThread = Thread.CurrentThread;
+                    RenderCore();
+                }
+                finally
+                {
+                    _safeThread = null;
+                }
             }
         }
         
@@ -180,5 +190,12 @@ namespace Avalonia.Rendering.Composition.Server
             using (RenderInterface.EnsureCurrent())
                 return RenderInterface.CreateRenderTarget(surfaces);
         }
+
+        public bool CheckAccess() => _safeThread == Thread.CurrentThread;
+        public void VerifyAccess()
+        {
+            if (!CheckAccess())
+                throw new InvalidOperationException("This object can be only accessed under compositor lock");
+        }
     }
 }