Suppress ExecutionContext flow for render scheduling (#21273)

* Add regression tests

* fix executioncontext leakage

* change DispatcherOperation ctor parameter to accept bool captureExecutionContext

src/Avalonia.Base/Media/MediaContext.cs

@@ -91,7 +91,9 @@ internal partial class MediaContext : ICompositorScheduler
         
         if (_inputMarkerOp == null)
         {
-            _inputMarkerOp = _dispatcher.InvokeAsync(_inputMarkerHandler, DispatcherPriority.Input);
+            _inputMarkerOp = new DispatcherOperation(_dispatcher, DispatcherPriority.Input, _inputMarkerHandler,
+                throwOnUiThread: true, captureExecutionContext: false);
+            _dispatcher.InvokeAsyncImpl(_inputMarkerOp, CancellationToken.None);
             _inputMarkerAddedAt = _time.Elapsed;
         }
         else if (!now && (_time.Elapsed - _inputMarkerAddedAt).TotalSeconds > MaxSecondsWithoutInput)
@@ -99,7 +101,7 @@ internal partial class MediaContext : ICompositorScheduler
             priority = DispatcherPriority.Input;
         }
 
-        var renderOp = new DispatcherOperation(_dispatcher, priority, _render, throwOnUiThread: true);
+        var renderOp = new DispatcherOperation(_dispatcher, priority, _render, throwOnUiThread: true, captureExecutionContext: false);
         _nextRenderOp = renderOp;
         _dispatcher.InvokeAsyncImpl(renderOp, CancellationToken.None);
     }

src/Avalonia.Base/Threading/DispatcherOperation.cs

@@ -44,18 +44,20 @@ public class DispatcherOperation
     private DispatcherPriority _priority;
     private readonly ExecutionContext? _executionContext;
 
-    internal DispatcherOperation(Dispatcher dispatcher, DispatcherPriority priority, Action callback, bool throwOnUiThread) :
+    internal DispatcherOperation(Dispatcher dispatcher, DispatcherPriority priority, Action callback, bool throwOnUiThread,
-        this(dispatcher, priority, throwOnUiThread)
+        bool captureExecutionContext = true) :
+        this(dispatcher, priority, throwOnUiThread, captureExecutionContext)
     {
         Callback = callback;
     }
 
-    private protected DispatcherOperation(Dispatcher dispatcher, DispatcherPriority priority, bool throwOnUiThread)
+    private protected DispatcherOperation(Dispatcher dispatcher, DispatcherPriority priority, bool throwOnUiThread,
+        bool captureExecutionContext = true)
     {
         ThrowOnUiThread = throwOnUiThread;
         Priority = priority;
         Dispatcher = dispatcher;
-        _executionContext = ExecutionContext.Capture();
+        _executionContext = captureExecutionContext ? ExecutionContext.Capture() : null;
     }
 
     internal string DebugDisplay

tests/Avalonia.Base.UnitTests/DispatcherTests.cs

@@ -6,6 +6,7 @@ using System.Globalization;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Avalonia.Controls;
 using Avalonia.Controls.Platform;
 using Avalonia.Threading;
 using Avalonia.UnitTests;
@@ -600,6 +601,19 @@ public partial class DispatcherTests
         public AsyncLocal<string?> AsyncLocalField { get; set; } = new AsyncLocal<string?>();
     }
 
+    private sealed class AsyncLocalMeasureControl(Func<string?> getValue, Action<string?> setValue) : Control
+    {
+        public bool RecordMeasure { get; set; }
+
+        protected override Size MeasureOverride(Size availableSize)
+        {
+            if (RecordMeasure)
+                setValue(getValue());
+
+            return new Size(1, 1);
+        }
+    }
+
     [Fact]
     public async Task ExecutionContextIsPreservedInDispatcherInvokeAsync()
     {
@@ -697,6 +711,76 @@ public partial class DispatcherTests
         Assert.Null(test);
     }
 
+    [Fact]
+    public void MediaContextRenderSchedulingDoesNotCaptureAmbientExecutionContext()
+    {
+        var impl = new SimpleDispatcherWithBackgroundProcessingImpl();
+        using var services = new DispatcherServices(impl);
+        Dispatcher.InitializeUIThreadDispatcher(impl);
+
+        var testObject = new AsyncLocalTestClass();
+        string? test = "Not measured";
+        var control = new AsyncLocalMeasureControl(() => testObject.AsyncLocalField.Value, value => test = value);
+        var root = new TestRoot { Child = control };
+
+        root.ExecuteInitialLayoutPass();
+        control.RecordMeasure = true;
+
+        Dispatcher.UIThread.Post(() =>
+        {
+            testObject.AsyncLocalField.Value = "Initial Value";
+            control.InvalidateMeasure();
+            testObject.AsyncLocalField.Value = null;
+        });
+
+        Assert.True(impl.AskedForSignal);
+        impl.ExecuteSignal();
+
+        Assert.Null(test);
+    }
+
+    [Fact]
+    public void MediaContextRenderSchedulingAllowsAlreadySuppressedExecutionContextFlow()
+    {
+        var impl = new SimpleDispatcherWithBackgroundProcessingImpl();
+        using var services = new DispatcherServices(impl);
+        Dispatcher.InitializeUIThreadDispatcher(impl);
+
+        var testObject = new AsyncLocalTestClass();
+        string? test = "Not measured";
+        Exception? schedulingException = null;
+        var control = new AsyncLocalMeasureControl(() => testObject.AsyncLocalField.Value, value => test = value);
+        var root = new TestRoot { Child = control };
+
+        root.ExecuteInitialLayoutPass();
+        control.RecordMeasure = true;
+
+        Dispatcher.UIThread.Post(() =>
+        {
+            testObject.AsyncLocalField.Value = "Initial Value";
+
+            try
+            {
+                using (ExecutionContext.SuppressFlow())
+                {
+                    control.InvalidateMeasure();
+                }
+            }
+            catch (Exception e)
+            {
+                schedulingException = e;
+            }
+
+            testObject.AsyncLocalField.Value = null;
+        });
+
+        Assert.True(impl.AskedForSignal);
+        impl.ExecuteSignal();
+
+        Assert.Null(schedulingException);
+        Assert.Null(test);
+    }
+
     [Fact]
     public async Task ExecutionContextCultureInfoIsPreservedInDispatcherInvokeAsync()
     {