Introduce Dispatcher.CurrentDispatcher, Dispatcher.FromThread, AvaloniaObject.Dispatcher (#18686)

* Introduce Dispatcher.CurrentDispatcher, FromThread, AvaloniaObject.Dispatcher, allow dispatcher usage before avalonia initialization, auto-create valid dispatchers for new threads.

* Remove async context usages, avoid scope splits

* Create InvalidTheme per dispatcher

* Update src/Avalonia.Base/Threading/Dispatcher.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/Avalonia.Base/Threading/Dispatcher.ThreadStorage.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* netstandard isn't there anymore

* Leftover code

Removed dispatcher mock setup and test services initialization.

* Remove dead code

* Dispatcher provides its own time provider

* Clean InputManager between tests

* Update API suppressions

---------

Co-authored-by: Julien Lebosquain <julien@lebosquain.net>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

api/Avalonia.nupkg.xml

@@ -307,6 +307,12 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Controls.Platform.ManagedDispatcherImpl</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Controls.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0001</DiagnosticId>
     <Target>T:Avalonia.Controls.Primitives.ChromeOverlayLayer</Target>
@@ -697,6 +703,12 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Controls.Platform.ManagedDispatcherImpl</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Controls.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Controls.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0001</DiagnosticId>
     <Target>T:Avalonia.Controls.Primitives.ChromeOverlayLayer</Target>

src/Android/Avalonia.Android/AndroidPlatform.cs

@@ -81,12 +81,12 @@ namespace Avalonia.Android
         {
             Options = AvaloniaLocator.Current.GetService<AndroidPlatformOptions>() ?? new AndroidPlatformOptions();
 
+            Dispatcher.InitializeUIThreadDispatcher(new AndroidDispatcherImpl());
             AvaloniaLocator.CurrentMutable
                 .Bind<ICursorFactory>().ToTransient<CursorFactory>()
                 .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformStub())
                 .Bind<IKeyboardDevice>().ToSingleton<AndroidKeyboardDevice>()
                 .Bind<IPlatformSettings>().ToSingleton<AndroidPlatformSettings>()
-                .Bind<IDispatcherImpl>().ToConstant(new AndroidDispatcherImpl())
                 .Bind<IPlatformIconLoader>().ToSingleton<PlatformIconLoaderStub>()
                 .Bind<IRenderTimer>().ToConstant(new ChoreographerTimer())
                 .Bind<PlatformHotkeyConfiguration>().ToSingleton<PlatformHotkeyConfiguration>()

src/Avalonia.Base/AvaloniaObject.cs

@@ -34,7 +34,6 @@ namespace Avalonia
         /// </summary>
         public AvaloniaObject()
         {
-            VerifyAccess();
             _values = new ValueStore(this);
         }
 
@@ -109,16 +108,22 @@ namespace Avalonia
         /// </summary>
         internal string DebugDisplay => GetDebugDisplay(true);
 
+        /// <summary>
+        ///     Returns the <see cref="Dispatcher"/> that this
+        ///     <see cref="AvaloniaObject"/> is associated with.
+        /// </summary>
+        public Dispatcher Dispatcher { get; } = Dispatcher.CurrentDispatcher;
+        
         /// <summary>
         /// Returns a value indicating whether the current thread is the UI thread.
         /// </summary>
         /// <returns>true if the current thread is the UI thread; otherwise false.</returns>
-        public bool CheckAccess() => Dispatcher.UIThread.CheckAccess();
-
+        public bool CheckAccess() => Dispatcher.CheckAccess();
+        
         /// <summary>
         /// Checks that the current thread is the UI thread and throws if not.
         /// </summary>
-        public void VerifyAccess() => Dispatcher.UIThread.VerifyAccess();
+        public void VerifyAccess() => Dispatcher.VerifyAccess();
 
         /// <summary>
         /// Clears a <see cref="AvaloniaProperty"/>'s local value.

src/Avalonia.Base/Input/InputManager.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Input
     /// Receives input from the windowing subsystem and dispatches it to interested parties
     /// for processing.
     /// </summary>
-    internal class InputManager : IInputManager
+    internal class InputManager : IInputManager, IDisposable
     {
         private readonly LightweightSubject<RawInputEventArgs> _preProcess = new();
         private readonly LightweightSubject<RawInputEventArgs> _process = new();
@@ -36,5 +36,12 @@ namespace Avalonia.Input
             _process.OnNext(e);
             _postProcess.OnNext(e);
         }
+
+        public void Dispose()
+        {
+            _preProcess.OnCompleted();
+            _process.OnCompleted();
+            _postProcess.OnCompleted();
+        }
     }
 }

src/Avalonia.Base/Rendering/Composition/Transport/BatchStreamArrayPool.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
+using System.Threading;
 using Avalonia.Platform;
 using Avalonia.Threading;
 
@@ -30,9 +31,7 @@ internal abstract class BatchStreamPoolBase<T> : IDisposable
         var updateRef = new WeakReference<BatchStreamPoolBase<T>>(this);
         if (
             reclaimImmediately 
-            || (
-            AvaloniaLocator.Current.GetService<IPlatformThreadingInterface>() == null
-            && AvaloniaLocator.Current.GetService<IDispatcherImpl>() == null))
+            || Dispatcher.FromThread(Thread.CurrentThread) == null)
             _reclaimImmediately = true;
         else
             StartUpdateTimer(startTimer, updateRef);

src/Avalonia.Base/StyledElement.cs

@@ -76,7 +76,7 @@ namespace Avalonia
         public static readonly StyledProperty<ControlTheme?> ThemeProperty =
             AvaloniaProperty.Register<StyledElement, ControlTheme?>(nameof(Theme));
 
-        private static readonly ControlTheme s_invalidTheme = new ControlTheme();
+        [ThreadStatic] private static ControlTheme? s_invalidTheme;
         private int _initCount;
         private string? _name;
         private Classes? _classes;
@@ -332,6 +332,9 @@ namespace Avalonia
         /// <inheritdoc/>
         IStyleHost? IStyleHost.StylingParent => (IStyleHost?)InheritanceParent;
 
+        internal static ControlTheme InvalidTheme
+            => s_invalidTheme ??= new();
+
         /// <inheritdoc/>
         public virtual void BeginInit()
         {
@@ -666,10 +669,10 @@ namespace Avalonia
                 if (this.TryFindResource(key, out var value) && value is ControlTheme t)
                     _implicitTheme = t;
                 else
-                    _implicitTheme = s_invalidTheme;
+                    _implicitTheme = InvalidTheme;
             }
 
-            if (_implicitTheme != s_invalidTheme)
+            if (_implicitTheme != InvalidTheme)
                 return _implicitTheme;
 
             return null;
@@ -828,11 +831,11 @@ namespace Avalonia
                 return;
 
             // Refetch the implicit theme.
-            var oldImplicitTheme = _implicitTheme == s_invalidTheme ? null : _implicitTheme;
+            var oldImplicitTheme = _implicitTheme == InvalidTheme ? null : _implicitTheme;
             _implicitTheme = null;
             GetEffectiveTheme();
 
-            var newImplicitTheme = _implicitTheme == s_invalidTheme ? null : _implicitTheme;
+            var newImplicitTheme = _implicitTheme == InvalidTheme ? null : _implicitTheme;
 
             // If the implicit theme has changed, detach the existing theme.
             if (newImplicitTheme != oldImplicitTheme)

src/Avalonia.Base/Threading/Dispatcher.Queue.cs

@@ -12,7 +12,7 @@ public partial class Dispatcher
     private bool _explicitBackgroundProcessingRequested;
     private const int MaximumInputStarvationTimeInFallbackMode = 50;
     private const int MaximumInputStarvationTimeInExplicitProcessingExplicitMode = 50;
-    private readonly int _maximumInputStarvationTime;
+    private int _maximumInputStarvationTime;
     
     void RequestBackgroundProcessing()
     {
@@ -101,9 +101,9 @@ public partial class Dispatcher
 
     internal static void ResetBeforeUnitTests()
     {
-        s_uiThread = null;
+        ResetGlobalState();
     }
-    
+
     internal static void ResetForUnitTests()
     {
         if (s_uiThread == null)
@@ -122,14 +122,14 @@ public partial class Dispatcher
             if (job == null || job.Priority <= DispatcherPriority.Inactive)
             {
                 s_uiThread.ShutdownImpl();
-                s_uiThread = null;
+                ResetGlobalState();
                 return;
             }
 
             s_uiThread.ExecuteJob(job);
         }
-
     }
+
     
     private void ExecuteJob(DispatcherOperation job)
     {

src/Avalonia.Base/Threading/Dispatcher.ThreadStorage.cs

@@ -0,0 +1,95 @@
+using System;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Avalonia.Controls.Platform;
+using Avalonia.Metadata;
+using Avalonia.Platform;
+using Avalonia.Utilities;
+
+namespace Avalonia.Threading;
+
+public partial class Dispatcher
+{
+    [ThreadStatic]
+    private static DispatcherReferenceStorage? s_currentThreadDispatcher;
+    private static readonly object s_globalLock = new();
+    private static readonly ConditionalWeakTable<Thread, DispatcherReferenceStorage> s_dispatchers = new();
+    
+    private static Dispatcher? s_uiThread;
+
+    // This class is needed PURELY for ResetForUnitTests, so we can reset s_currentThreadDispatcher for all threads
+    class DispatcherReferenceStorage
+    {
+        public WeakReference<Dispatcher> Reference = new(null!);
+    }
+    
+    public static Dispatcher CurrentDispatcher
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get
+        {
+            if (s_currentThreadDispatcher?.Reference.TryGetTarget(out var dispatcher) == true)
+                return dispatcher;
+
+            return new Dispatcher(null);
+        }
+    }
+
+    public static Dispatcher? FromThread(Thread thread)
+    {
+        lock (s_globalLock)
+        {
+            if (s_dispatchers.TryGetValue(thread, out var reference) && reference.Reference.TryGetTarget(out var dispatcher) == true)
+                return dispatcher;
+            return null;
+        }
+    }
+    
+    public static Dispatcher UIThread
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get
+        {
+            static Dispatcher GetUIThreadDispatcherSlow()
+            {
+                lock (s_globalLock)
+                {
+                    return s_uiThread ?? CurrentDispatcher;
+                }
+            }
+            return s_uiThread ?? GetUIThreadDispatcherSlow();
+        }
+    }
+
+    internal static Dispatcher? TryGetUIThread()
+    {
+        lock (s_globalLock)
+            return s_uiThread;
+    }
+    
+    [PrivateApi]
+    public static void InitializeUIThreadDispatcher(IPlatformThreadingInterface impl) =>
+        InitializeUIThreadDispatcher(new LegacyDispatcherImpl(impl));
+
+    [PrivateApi]
+    public static void InitializeUIThreadDispatcher(IDispatcherImpl impl)
+    {
+        UIThread.VerifyAccess();
+        if (UIThread._initialized)
+            throw new InvalidOperationException("UI thread dispatcher is already initialized");
+        UIThread.ReplaceImplementation(impl);
+    }
+
+    private static void ResetGlobalState()
+    {
+        lock (s_globalLock)
+        {
+            foreach (var store in s_dispatchers)
+                store.Value.Reference = new(null!);
+            s_dispatchers.Clear();
+
+            s_currentThreadDispatcher = null;
+            s_uiThread = null;
+        }
+    }
+}

src/Avalonia.Base/Threading/Dispatcher.Timers.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 
 namespace Avalonia.Threading;
@@ -15,7 +16,8 @@ public partial class Dispatcher
     private long? _dueTimeForBackgroundProcessing;
     private long? _osTimerSetTo;
 
-    internal long Now => _impl.Now;
+    private readonly Func<long> _timeProvider;
+    internal long Now => _timeProvider();
 
     private void UpdateOSTimer()
     {
@@ -26,6 +28,7 @@ public partial class Dispatcher
                 _dueTimeForTimers ?? _dueTimeForBackgroundProcessing;
         if (_osTimerSetTo == nextDueTime)
             return;
+
         _impl.UpdateTimer(_osTimerSetTo = nextDueTime);
     }
 
@@ -114,7 +117,8 @@ public partial class Dispatcher
         bool needToProcessQueue = false;
         lock (InstanceLock)
         {
-            _impl.UpdateTimer(_osTimerSetTo = null);
+            _impl.UpdateTimer(null);
+            _osTimerSetTo = null;
             needToPromoteTimers = _dueTimeForTimers.HasValue && _dueTimeForTimers.Value <= Now;
             if (needToPromoteTimers)
                 _dueTimeForTimers = null;

src/Avalonia.Base/Threading/Dispatcher.cs

@@ -3,7 +3,10 @@ using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Threading;
+using Avalonia.Controls.Platform;
+using Avalonia.Metadata;
 using Avalonia.Platform;
+using Avalonia.Utilities;
 
 namespace Avalonia.Threading;
 
@@ -17,63 +20,60 @@ namespace Avalonia.Threading;
 public partial class Dispatcher : IDispatcher
 {
     private IDispatcherImpl _impl;
+    private bool _initialized;
     internal object InstanceLock { get; } = new();
     private IControlledDispatcherImpl? _controlledImpl;
-    private static Dispatcher? s_uiThread;
     private IDispatcherImplWithPendingInput? _pendingInputImpl;
-    private readonly IDispatcherImplWithExplicitBackgroundProcessing? _backgroundProcessingImpl;
+    private IDispatcherImplWithExplicitBackgroundProcessing? _backgroundProcessingImpl;
+    private readonly Thread _thread;
 
     private readonly AvaloniaSynchronizationContext?[] _priorityContexts =
         new AvaloniaSynchronizationContext?[DispatcherPriority.MaxValue - DispatcherPriority.MinValue + 1];
 
-    internal Dispatcher(IDispatcherImpl impl)
+    internal Dispatcher(IDispatcherImpl? impl)
     {
-        _impl = impl;
-        impl.Timer += OnOSTimer;
-        impl.Signaled += Signaled;
-        _controlledImpl = _impl as IControlledDispatcherImpl;
-        _pendingInputImpl = _impl as IDispatcherImplWithPendingInput;
-        _backgroundProcessingImpl = _impl as IDispatcherImplWithExplicitBackgroundProcessing;
-        _maximumInputStarvationTime = _backgroundProcessingImpl == null ?
-            MaximumInputStarvationTimeInFallbackMode :
-            MaximumInputStarvationTimeInExplicitProcessingExplicitMode;
-        if (_backgroundProcessingImpl != null)
-            _backgroundProcessingImpl.ReadyForBackgroundProcessing += OnReadyForExplicitBackgroundProcessing;
-
-        _unhandledExceptionEventArgs = new DispatcherUnhandledExceptionEventArgs(this);
-        _exceptionFilterEventArgs = new DispatcherUnhandledExceptionFilterEventArgs(this);
-    }
-    
-    public static Dispatcher UIThread
-    {
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get
+#if DEBUG
+        if (AvaloniaLocator.Current.GetService<IDispatcherImpl>() != null
+            || AvaloniaLocator.Current.GetService<IPlatformThreadingInterface>() != null)
+            throw new InvalidOperationException(
+                "Registering IDispatcherImpl or IPlatformThreadingInterface via locator is no longer valid");
+#endif
+        lock (s_globalLock)
         {
-            return s_uiThread ??= CreateUIThreadDispatcher();
-        }
-    }
+            _thread = Thread.CurrentThread;
+            if (FromThread(_thread) != null)
+                throw new InvalidOperationException("The current thread already has a dispatcher");
 
-    public bool SupportsRunLoops => _controlledImpl != null;
+            // The first created dispatcher becomes "UI thread one"
+            s_uiThread ??= this;
 
-    [MethodImpl(MethodImplOptions.NoInlining)]
-    private static Dispatcher CreateUIThreadDispatcher()
-    {
-        var impl = AvaloniaLocator.Current.GetService<IDispatcherImpl>();
-        if (impl == null)
+            s_dispatchers.Remove(Thread.CurrentThread);
+            s_dispatchers.Add(Thread.CurrentThread,
+                s_currentThreadDispatcher = new() { Reference = new WeakReference<Dispatcher>(this) });
+        }
+
+        if (impl is null)
         {
-            var platformThreading = AvaloniaLocator.Current.GetService<IPlatformThreadingInterface>();
-            if (platformThreading != null)
-                impl = new LegacyDispatcherImpl(platformThreading);
-            else
-                impl = new NullDispatcherImpl();
+            var st = Stopwatch.StartNew();
+            _timeProvider = () => st.ElapsedMilliseconds;
         }
-        return new Dispatcher(impl);
+        else
+            _timeProvider = () => impl.Now;
+
+        _impl = null!; // Set by ReplaceImplementation
+        ReplaceImplementation(impl);
+        
+
+        _unhandledExceptionEventArgs = new DispatcherUnhandledExceptionEventArgs(this);
+        _exceptionFilterEventArgs = new DispatcherUnhandledExceptionFilterEventArgs(this);
     }
 
+    public bool SupportsRunLoops => _controlledImpl != null;
+
     /// <summary>
     /// Checks that the current thread is the UI thread.
     /// </summary>
-    public bool CheckAccess() => _impl.CurrentThreadIsLoopThread;
+    public bool CheckAccess() => Thread.CurrentThread == _thread;
 
     /// <summary>
     /// Checks that the current thread is the UI thread and throws if not.
@@ -89,15 +89,64 @@ public partial class Dispatcher : IDispatcher
             [DoesNotReturn]
             [MethodImpl(MethodImplOptions.NoInlining)]
             static void ThrowVerifyAccess()
-                => throw new InvalidOperationException("Call from invalid thread");
+                => throw new InvalidOperationException("The calling thread cannot access this object because a different thread owns it.");
             ThrowVerifyAccess();
         }
     }
 
+    public Thread Thread => _thread;
+
     internal AvaloniaSynchronizationContext GetContextWithPriority(DispatcherPriority priority)
     {
         DispatcherPriority.Validate(priority, nameof(priority));
         var index = priority - DispatcherPriority.MinValue;
         return _priorityContexts[index] ??= new(this, priority);
     }
+
+    [PrivateApi]
+    public IDispatcherImpl PlatformImpl => _impl;
+    
+    private void ReplaceImplementation(IDispatcherImpl? impl)
+    {
+        // TODO: Consider moving the helper out of Avalonia.Win32 so
+        // it's usable earlier
+        using var _ = NonPumpingLockHelper.Use();
+
+
+        if (impl?.CurrentThreadIsLoopThread == false)
+            throw new InvalidOperationException("IDispatcherImpl belongs to a different thread");
+        
+        if (_impl != null!) // Null in ctor
+        {
+            _impl.Timer -= OnOSTimer;
+            _impl.Signaled -= Signaled;
+            if (_backgroundProcessingImpl != null)
+                _backgroundProcessingImpl.ReadyForBackgroundProcessing -= OnReadyForExplicitBackgroundProcessing;
+            _impl = null!;
+            _controlledImpl = null;
+            _pendingInputImpl = null;
+            _backgroundProcessingImpl = null;
+        }
+
+        if (impl != null)
+            _initialized = true;
+        else
+            impl = new ManagedDispatcherImpl(null);
+        _impl = impl;
+        
+        impl.Timer += OnOSTimer;
+        impl.Signaled += Signaled;
+        _controlledImpl = _impl as IControlledDispatcherImpl;
+        _pendingInputImpl = _impl as IDispatcherImplWithPendingInput;
+        _backgroundProcessingImpl = _impl as IDispatcherImplWithExplicitBackgroundProcessing;
+        _maximumInputStarvationTime = _backgroundProcessingImpl == null ?
+            MaximumInputStarvationTimeInFallbackMode :
+            MaximumInputStarvationTimeInExplicitProcessingExplicitMode;
+        if (_backgroundProcessingImpl != null)
+            _backgroundProcessingImpl.ReadyForBackgroundProcessing += OnReadyForExplicitBackgroundProcessing;
+        if (_signaled)
+            _impl.Signal();
+        _osTimerSetTo = null;
+        UpdateOSTimer();
+    }
 }

src/Avalonia.Base/Threading/IDispatcherImpl.cs

@@ -80,33 +80,4 @@ internal class LegacyDispatcherImpl : IDispatcherImpl
         _timer = null;
         Timer?.Invoke();
     }
-}
-
-internal sealed class NullDispatcherImpl : IDispatcherImpl
-{
-    public bool CurrentThreadIsLoopThread => true;
-
-    public void Signal()
-    {
-        
-    }
-    
-    public event Action? Signaled
-    {
-        add { }
-        remove { }
-    }
-
-    public event Action? Timer
-    {
-        add { }
-        remove { }
-    }
-
-    public long Now => 0;
-
-    public void UpdateTimer(long? dueTimeInMs)
-    {
-        
-    }
-}
+}

src/Avalonia.DesignerSupport/Remote/PreviewerWindowingPlatform.cs

@@ -55,7 +55,6 @@ namespace Avalonia.DesignerSupport.Remote
                 .Bind<ICursorFactory>().ToSingleton<CursorFactoryStub>()
                 .Bind<IKeyboardDevice>().ToConstant(Keyboard)
                 .Bind<IPlatformSettings>().ToSingleton<DefaultPlatformSettings>()
-                .Bind<IDispatcherImpl>().ToConstant(new ManagedDispatcherImpl(null))
                 .Bind<IRenderTimer>().ToConstant(new UiThreadRenderTimer(60))
                 .Bind<IWindowingPlatform>().ToConstant(instance)
                 .Bind<IPlatformIconLoader>().ToSingleton<IconLoaderStub>()

src/Avalonia.Native/AvaloniaNativePlatform.cs

@@ -114,8 +114,8 @@ namespace Avalonia.Native
             var clipboardImpl = new ClipboardImpl(_factory.CreateClipboard());
             var clipboard = new Clipboard(clipboardImpl);
 
+            Dispatcher.InitializeUIThreadDispatcher(new DispatcherImpl(_factory.CreatePlatformThreadingInterface()));
             AvaloniaLocator.CurrentMutable
-                .Bind<IDispatcherImpl>().ToConstant(new DispatcherImpl(_factory.CreatePlatformThreadingInterface()))
                 .Bind<ICursorFactory>().ToConstant(new CursorFactory(_factory.CreateCursorFactory()))
                 .Bind<IScreenImpl>().ToConstant(new ScreenImpl(_factory.CreateScreens))
                 .Bind<IPlatformIconLoader>().ToSingleton<IconLoader>()

src/Avalonia.Native/CallbackBase.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Runtime.ExceptionServices;
+using System.Threading;
 using Avalonia.MicroCom;
 using Avalonia.Platform;
 using Avalonia.Threading;
@@ -11,7 +12,7 @@ namespace Avalonia.Native
     {
         public void RaiseException(Exception e)
         {
-            if (AvaloniaLocator.Current.GetService<IDispatcherImpl>() is DispatcherImpl dispatcherImpl)
+            if(Dispatcher.FromThread(Thread.CurrentThread) is { PlatformImpl: DispatcherImpl dispatcherImpl })
             {
                 dispatcherImpl.PropagateCallbackException(ExceptionDispatchInfo.Capture(e));
             }

src/Avalonia.X11/X11Platform.cs

@@ -42,6 +42,7 @@ namespace Avalonia.X11
         public X11Globals Globals { get; private set; } = null!;
         public XResources Resources { get; private set; } = null!;
         public ManualRawEventGrouperDispatchQueue EventGrouperDispatchQueue { get; } = new();
+        public IX11PlatformDispatcher DispatcherImpl { get; private set; } = null!;
 
         public void Initialize(X11PlatformOptions options)
         {
@@ -79,10 +80,12 @@ namespace Avalonia.X11
             var clipboard = new Input.Platform.Clipboard(clipboardImpl);
 
             AvaloniaLocator.CurrentMutable.BindToSelf(this)
-                .Bind<IWindowingPlatform>().ToConstant(this)
-                .Bind<IDispatcherImpl>().ToConstant<IDispatcherImpl>(options.UseGLibMainLoop
-                    ? new GlibDispatcherImpl(this)
-                    : new X11PlatformThreading(this))
+                .Bind<IWindowingPlatform>().ToConstant(this);
+            DispatcherImpl = options.UseGLibMainLoop
+                ? new GlibDispatcherImpl(this)
+                : new X11PlatformThreading(this);
+            Dispatcher.InitializeUIThreadDispatcher(DispatcherImpl);
+            AvaloniaLocator.CurrentMutable
                 .Bind<IRenderTimer>().ToConstant(timer)
                 .Bind<PlatformHotkeyConfiguration>().ToConstant(new PlatformHotkeyConfiguration(KeyModifiers.Control))
                 .Bind<KeyGestureFormatInfo>().ToConstant(new KeyGestureFormatInfo(new Dictionary<Key, string>() { }, meta: "Super"))

src/Avalonia.X11/XEmbedPlug.cs

@@ -13,19 +13,20 @@ public class XEmbedPlug : IDisposable
     private Color _backgroundColor;
     private readonly X11Info _x11;
     private readonly X11Window.XEmbedClientWindowMode _mode;
+    private readonly AvaloniaX11Platform _platform;
 
     private XEmbedPlug(IntPtr? parentXid)
     {
-        var platform = AvaloniaLocator.Current.GetRequiredService<AvaloniaX11Platform>();
+        _platform = AvaloniaLocator.Current.GetRequiredService<AvaloniaX11Platform>();
         _mode = new X11Window.XEmbedClientWindowMode();
-        _root = new EmbeddableControlRoot(new X11Window(platform, null, _mode));
+        _root = new EmbeddableControlRoot(new X11Window(_platform, null, _mode));
         _root.Prepare();
-        _x11 = platform.Info;
+        _x11 = _platform.Info;
         if (parentXid.HasValue)
-            XLib.XReparentWindow(platform.Display, Handle, parentXid.Value, 0, 0);
+            XLib.XReparentWindow(_platform.Display, Handle, parentXid.Value, 0, 0);
         
         // Make sure that the newly created XID is visible for other clients
-        XLib.XSync(platform.Display, false);
+        XLib.XSync(_platform.Display, false);
     }
 
     private EmbeddableControlRoot Root
@@ -60,8 +61,7 @@ public class XEmbedPlug : IDisposable
 
     public void ProcessInteractiveResize(PixelSize size)
     {
-        
-        var events = (IX11PlatformDispatcher)AvaloniaLocator.Current.GetRequiredService<IDispatcherImpl>();
+        var events = _platform.DispatcherImpl;
         events.EventDispatcher.DispatchX11Events(CancellationToken.None);
         _mode.ProcessInteractiveResize(size);
         Dispatcher.UIThread.RunJobs(DispatcherPriority.UiThreadRender);

src/Browser/Avalonia.Browser/WindowingPlatform.cs

@@ -97,15 +97,17 @@ internal class BrowserWindowingPlatform : IWindowingPlatform
             .Bind<PlatformHotkeyConfiguration>().ToSingleton<PlatformHotkeyConfiguration>()
             .Bind<KeyGestureFormatInfo>().ToConstant(new KeyGestureFormatInfo(new Dictionary<Key, string>() { }))
             .Bind<IActivatableLifetime>().ToSingleton<BrowserActivatableLifetime>();
+        
         if (IsManagedDispatcherEnabled)
         {
             EventGrouperDispatchQueue = new();
-            AvaloniaLocator.CurrentMutable.Bind<IDispatcherImpl>().ToConstant(
-                new ManagedDispatcherImpl(new ManualRawEventGrouperDispatchQueueDispatcherInputProvider(EventGrouperDispatchQueue)));
+            Dispatcher.InitializeUIThreadDispatcher(
+                new ManagedDispatcherImpl(
+                    new ManualRawEventGrouperDispatchQueueDispatcherInputProvider(EventGrouperDispatchQueue)));
         }
         else
         {
-            AvaloniaLocator.CurrentMutable.Bind<IDispatcherImpl>().ToSingleton<BrowserDispatcherImpl>();
+            Dispatcher.InitializeUIThreadDispatcher(new BrowserDispatcherImpl());
         }
 
         // GC thread is the same as the main one when MT is disabled

src/Headless/Avalonia.Headless/AvaloniaHeadlessPlatform.cs

@@ -79,7 +79,6 @@ namespace Avalonia.Headless
             var clipboard = new Clipboard(clipboardImpl);
 
             AvaloniaLocator.CurrentMutable
-                .Bind<IDispatcherImpl>().ToConstant(new ManagedDispatcherImpl(null))
                 .Bind<IClipboardImpl>().ToConstant(clipboardImpl)
                 .Bind<IClipboard>().ToConstant(clipboard)
                 .Bind<ICursorFactory>().ToSingleton<HeadlessCursorFactoryStub>()

src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs

@@ -62,8 +62,8 @@ namespace Avalonia.LinuxFramebuffer
                 ? new UiThreadRenderTimer(opts.Fps)
                 : new DefaultRenderTimer(opts.Fps);
             
+            Dispatcher.InitializeUIThreadDispatcher(new EpollDispatcherImpl(new ManualRawEventGrouperDispatchQueueDispatcherInputProvider(EventGrouperDispatchQueue)));
             AvaloniaLocator.CurrentMutable
-                .Bind<IDispatcherImpl>().ToConstant(new EpollDispatcherImpl(new ManualRawEventGrouperDispatchQueueDispatcherInputProvider(EventGrouperDispatchQueue)))
                 .Bind<IRenderTimer>().ToConstant(timer)
                 .Bind<ICursorFactory>().ToTransient<CursorFactoryStub>()
                 .Bind<IKeyboardDevice>().ToConstant(new KeyboardDevice())

src/Windows/Avalonia.Win32/Win32Platform.cs

@@ -85,6 +85,8 @@ namespace Avalonia.Win32
 
             SetDpiAwareness();
 
+            Dispatcher.InitializeUIThreadDispatcher(s_instance._dispatcher);
+            
             var renderTimer = options.ShouldRenderOnUIThread ? new UiThreadRenderTimer(60) : new DefaultRenderTimer(60);
             var clipboardImpl = new ClipboardImpl();
             var clipboard = new Clipboard(clipboardImpl);
@@ -96,7 +98,6 @@ namespace Avalonia.Win32
                 .Bind<IKeyboardDevice>().ToConstant(WindowsKeyboardDevice.Instance)
                 .Bind<IPlatformSettings>().ToSingleton<Win32PlatformSettings>()
                 .Bind<IScreenImpl>().ToSingleton<ScreenImpl>()
-                .Bind<IDispatcherImpl>().ToConstant(s_instance._dispatcher)
                 .Bind<IRenderTimer>().ToConstant(renderTimer)
                 .Bind<IWindowingPlatform>().ToConstant(s_instance)
                 .Bind<PlatformHotkeyConfiguration>().ToConstant(new PlatformHotkeyConfiguration(KeyModifiers.Control)

src/iOS/Avalonia.iOS/Platform.cs

@@ -77,6 +77,7 @@ namespace Avalonia.iOS
             Timer ??= new DisplayLinkTimer();
             var keyboard = new KeyboardDevice();
 
+            Dispatcher.InitializeUIThreadDispatcher(DispatcherImpl.Instance);
             AvaloniaLocator.CurrentMutable
                 .Bind<IPlatformGraphics>().ToConstant(Graphics)
                 .Bind<ICursorFactory>().ToConstant(new CursorFactoryStub())
@@ -93,7 +94,6 @@ namespace Avalonia.iOS
                         { Key.Up , "↑" }
                     }, ctrl: "⌃", meta: "⌘", shift: "⇧", alt: "⌥"))
                 .Bind<IRenderTimer>().ToConstant(Timer)
-                .Bind<IDispatcherImpl>().ToConstant(DispatcherImpl.Instance)
                 .Bind<IKeyboardDevice>().ToConstant(keyboard);
 
             if (appDelegate is not null)

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Binding.cs

@@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
 using System.Threading;
@@ -19,7 +20,7 @@ using Xunit;
 
 namespace Avalonia.Base.UnitTests
 {
-    public class AvaloniaObjectTests_Binding
+    public class AvaloniaObjectTests_Binding : ScopedTestBase
     {
         [Fact]
         public void Bind_Sets_Current_Value()
@@ -858,37 +859,28 @@ namespace Avalonia.Base.UnitTests
         [InlineData(BindingPriority.Style)]
         public void Typed_Bind_Executes_On_UIThread(BindingPriority priority)
         {
-            AsyncContext.Run(async () =>
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
                 var source = new Subject<string>();
                 var currentThreadId = Thread.CurrentThread.ManagedThreadId;
                 var raised = 0;
 
-                var dispatcherMock = new Mock<IDispatcherImpl>();
-                dispatcherMock.SetupGet(mock => mock.CurrentThreadIsLoopThread)
-                    .Returns(() => Thread.CurrentThread.ManagedThreadId == currentThreadId);
-
-                var services = new TestServices(
-                    dispatcherImpl: dispatcherMock.Object);
-
                 target.PropertyChanged += (s, e) =>
                 {
                     Assert.Equal(currentThreadId, Thread.CurrentThread.ManagedThreadId);
                     ++raised;
                 };
 
-                using (UnitTestApplication.Start(services))
-                {
-                    target.Bind(Class1.FooProperty, source, priority);
 
-                    await Task.Run(() => source.OnNext("foobar"));
-                    Dispatcher.UIThread.RunJobs();
+                target.Bind(Class1.FooProperty, source, priority);
 
-                    Assert.Equal("foobar", target.GetValue(Class1.FooProperty));
-                    Assert.Equal(1, raised);
-                }
-            });
+                ThreadRunHelper.RunOnDedicatedThreadAndWait(() => source.OnNext("foobar"));
+                Dispatcher.UIThread.RunJobs(null, TestContext.Current.CancellationToken);
+
+                Assert.Equal("foobar", target.GetValue(Class1.FooProperty));
+                Assert.Equal(1, raised);
+            }
         }
 
         [Theory]
@@ -896,37 +888,28 @@ namespace Avalonia.Base.UnitTests
         [InlineData(BindingPriority.Style)]
         public void Untyped_Bind_Executes_On_UIThread(BindingPriority priority)
         {
-            AsyncContext.Run(async () =>
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
                 var source = new Subject<object>();
                 var currentThreadId = Thread.CurrentThread.ManagedThreadId;
                 var raised = 0;
 
-                var dispatcherMock = new Mock<IDispatcherImpl>();
-                dispatcherMock.SetupGet(mock => mock.CurrentThreadIsLoopThread)
-                    .Returns(() => Thread.CurrentThread.ManagedThreadId == currentThreadId);
-
-                var services = new TestServices(
-                    dispatcherImpl: dispatcherMock.Object);
-
                 target.PropertyChanged += (s, e) =>
                 {
                     Assert.Equal(currentThreadId, Thread.CurrentThread.ManagedThreadId);
                     ++raised;
                 };
 
-                using (UnitTestApplication.Start(services))
-                {
-                    target.Bind(Class1.FooProperty, source, priority);
 
-                    await Task.Run(() => source.OnNext("foobar"));
-                    Dispatcher.UIThread.RunJobs();
+                target.Bind(Class1.FooProperty, source, priority);
 
-                    Assert.Equal("foobar", target.GetValue(Class1.FooProperty));
-                    Assert.Equal(1, raised);
-                }
-            });
+                ThreadRunHelper.RunOnDedicatedThreadAndWait(() => source.OnNext("foobar"));
+                Dispatcher.UIThread.RunJobs(null, TestContext.Current.CancellationToken);
+
+                Assert.Equal("foobar", target.GetValue(Class1.FooProperty));
+                Assert.Equal(1, raised);
+            }
         }
 
         [Theory]
@@ -934,59 +917,41 @@ namespace Avalonia.Base.UnitTests
         [InlineData(BindingPriority.Style)]
         public void BindingValue_Bind_Executes_On_UIThread(BindingPriority priority)
         {
-            AsyncContext.Run(async () =>
-            {
-                var target = new Class1();
-                var source = new Subject<BindingValue<string>>();
-                var currentThreadId = Thread.CurrentThread.ManagedThreadId;
-                var raised = 0;
-
-                var threadingInterfaceMock = new Mock<IDispatcherImpl>();
-                threadingInterfaceMock.SetupGet(mock => mock.CurrentThreadIsLoopThread)
-                    .Returns(() => Thread.CurrentThread.ManagedThreadId == currentThreadId);
-
-                var services = new TestServices(
-                    dispatcherImpl: threadingInterfaceMock.Object);
+            using var _ = UnitTestApplication.Start();
+            var target = new Class1();
+            var source = new Subject<BindingValue<string>>();
+            var currentThreadId = Thread.CurrentThread.ManagedThreadId;
+            var raised = 0;
 
-                target.PropertyChanged += (s, e) =>
-                {
-                    Assert.Equal(currentThreadId, Thread.CurrentThread.ManagedThreadId);
-                    ++raised;
-                };
+            target.PropertyChanged += (s, e) =>
+            {
+                Assert.Equal(currentThreadId, Thread.CurrentThread.ManagedThreadId);
+                ++raised;
+            };
 
-                using (UnitTestApplication.Start(services))
-                {
-                    target.Bind(Class1.FooProperty, source, priority);
+            target.Bind(Class1.FooProperty, source, priority);
 
-                    await Task.Run(() => source.OnNext("foobar"));
-                    Dispatcher.UIThread.RunJobs();
+            ThreadRunHelper.RunOnDedicatedThreadAndWait(() => source.OnNext("foobar"));
+            Dispatcher.UIThread.RunJobs(null, TestContext.Current.CancellationToken);
 
-                    Assert.Equal("foobar", target.GetValue(Class1.FooProperty));
-                    Assert.Equal(1, raised);
-                }
-            });
+            Assert.Equal("foobar", target.GetValue(Class1.FooProperty));
+            Assert.Equal(1, raised);
         }
 
         [Fact]
-        public async Task Bind_With_Scheduler_Executes_On_UI_Thread()
+        [SuppressMessage("Usage", "xUnit1031:Do not use blocking task operations in test method", Justification = "Explicit threading test")]
+        public void Bind_With_Scheduler_Executes_On_UI_Thread()
         {
+            using var _ = UnitTestApplication.Start();
+
             var target = new Class1();
             var source = new Subject<double>();
-            var currentThreadId = Thread.CurrentThread.ManagedThreadId;
-
-            var threadingInterfaceMock = new Mock<IDispatcherImpl>();
-            threadingInterfaceMock.SetupGet(mock => mock.CurrentThreadIsLoopThread)
-                .Returns(() => Thread.CurrentThread.ManagedThreadId == currentThreadId);
-
-            var services = new TestServices(
-                dispatcherImpl: threadingInterfaceMock.Object);
-
-            using (UnitTestApplication.Start(services))
-            {
-                target.Bind(Class1.QuxProperty, source);
+            target.Bind(Class1.QuxProperty, source);
 
-                await Task.Run(() => source.OnNext(6.7), TestContext.Current.CancellationToken);
-            }
+            ThreadRunHelper.RunOnDedicatedThread(() => source.OnNext(6.7)).GetAwaiter().GetResult();
+            Assert.NotEqual(6.7, target.GetValue(Class1.QuxProperty));
+            Dispatcher.UIThread.RunJobs(null, TestContext.Current.CancellationToken);
+            Assert.Equal(6.7, target.GetValue(Class1.QuxProperty));
         }
 
         [Fact]

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Direct.cs

@@ -492,19 +492,13 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Bind_Executes_On_UIThread()
         {
-            AsyncContext.Run(async () =>
+            using(UnitTestApplication.Start())
             {
                 var target = new Class1();
                 var source = new Subject<object>();
                 var currentThreadId = Thread.CurrentThread.ManagedThreadId;
                 var raised = 0;
 
-                var dispatcherMock = new Mock<IDispatcherImpl>();
-                dispatcherMock.SetupGet(mock => mock.CurrentThreadIsLoopThread)
-                    .Returns(() => Thread.CurrentThread.ManagedThreadId == currentThreadId);
-
-                var services = new TestServices(
-                    dispatcherImpl: dispatcherMock.Object);
 
                 target.PropertyChanged += (s, e) =>
                 {
@@ -512,17 +506,15 @@ namespace Avalonia.Base.UnitTests
                     ++raised;
                 };
 
-                using (UnitTestApplication.Start(services))
-                {
-                    target.Bind(Class1.FooProperty, source);
+                
+                target.Bind(Class1.FooProperty, source);
 
-                    await Task.Run(() => source.OnNext("foobar"));
-                    Dispatcher.UIThread.RunJobs();
+                ThreadRunHelper.RunOnDedicatedThreadAndWait(() => source.OnNext("foobar"));
+                Dispatcher.UIThread.RunJobs(null, TestContext.Current.CancellationToken);
 
-                    Assert.Equal("foobar", target.Foo);
-                    Assert.Equal(1, raised);
-                }
-            });
+                Assert.Equal("foobar", target.Foo);
+                Assert.Equal(1, raised);
+            }
         }
 
         [Fact]

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Threading.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Reactive.Subjects;
+using System.Runtime.ExceptionServices;
 using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Platform;
@@ -9,49 +10,43 @@ using Xunit;
 
 namespace Avalonia.Base.UnitTests
 {
-    public class AvaloniaObjectTests_Threading
+    public class AvaloniaObjectTests_Threading : ScopedTestBase
     {
-        private TestDipatcherImpl _threading = new(true);
-
-        [Fact]
-        public void AvaloniaObject_Constructor_Should_Throw()
+        void AssertThrowsOnDifferentThread(Action cb)
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: new TestDipatcherImpl())))
-            {
-                Assert.Throws<InvalidOperationException>(() => new Class1());
-            }
+            Assert.Throws<InvalidOperationException>(() =>
+                ThreadRunHelper.RunOnDedicatedThread(cb).GetAwaiter().GetResult());
         }
 
         [Fact]
         public void StyledProperty_GetValue_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.GetValue(Class1.StyledProperty));
+                target.GetValue(Class1.StyledProperty);
+
+                AssertThrowsOnDifferentThread(() => target.GetValue(Class1.StyledProperty));
             }
         }
 
         [Fact]
         public void StyledProperty_SetValue_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.SetValue(Class1.StyledProperty, "foo"));
+                AssertThrowsOnDifferentThread(() => target.SetValue(Class1.StyledProperty, "foo"));
             }
         }
 
         [Fact]
         public void Setting_StyledProperty_Binding_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => 
+                AssertThrowsOnDifferentThread(() =>
                     target.Bind(
                         Class1.StyledProperty,
                         new BehaviorSubject<string>("foo")));
@@ -61,55 +56,50 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void StyledProperty_ClearValue_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.ClearValue(Class1.StyledProperty));
+                AssertThrowsOnDifferentThread(() => target.ClearValue(Class1.StyledProperty));
             }
         }
 
         [Fact]
         public void StyledProperty_IsSet_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.IsSet(Class1.StyledProperty));
+                AssertThrowsOnDifferentThread(() => target.IsSet(Class1.StyledProperty));
             }
         }
 
         [Fact]
         public void DirectProperty_GetValue_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.GetValue(Class1.DirectProperty));
+                AssertThrowsOnDifferentThread(() => target.GetValue(Class1.DirectProperty));
             }
         }
 
         [Fact]
         public void DirectProperty_SetValue_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.SetValue(Class1.DirectProperty, "foo"));
+                AssertThrowsOnDifferentThread(() => target.SetValue(Class1.DirectProperty, "foo"));
             }
         }
 
         [Fact]
         public void Setting_DirectProperty_Binding_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() =>
+                AssertThrowsOnDifferentThread(() =>
                     target.Bind(
                         Class1.DirectProperty,
                         new BehaviorSubject<string>("foo")));
@@ -119,22 +109,20 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void DirectProperty_ClearValue_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.ClearValue(Class1.DirectProperty));
+                AssertThrowsOnDifferentThread(() => target.ClearValue(Class1.DirectProperty));
             }
         }
 
         [Fact]
         public void DirectProperty_IsSet_Should_Throw()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: _threading)))
+            using (UnitTestApplication.Start())
             {
                 var target = new Class1();
-                _threading.CurrentThreadIsLoopThread = false;
-                Assert.Throws<InvalidOperationException>(() => target.IsSet(Class1.DirectProperty));
+                AssertThrowsOnDifferentThread(() => target.IsSet(Class1.DirectProperty));
             }
         }
 
@@ -146,27 +134,5 @@ namespace Avalonia.Base.UnitTests
             public static readonly DirectProperty<Class1, string?> DirectProperty =
                 AvaloniaProperty.RegisterDirect<Class1, string?>("Qux", _ => null, (o, v) => { });
         }
-
-        private class TestDipatcherImpl : IDispatcherImpl
-        {
-
-            public TestDipatcherImpl(bool isLoopThread = false)
-            {
-                CurrentThreadIsLoopThread = isLoopThread;
-            }
-
-            public bool CurrentThreadIsLoopThread { get; set; }
-
-            public event Action? Signaled { add { } remove { } }
-            public event Action? Timer { add { } remove { } }
-            public long Now => 0;
-            public void UpdateTimer(long? dueTimeInMs)
-            {
-                throw new NotImplementedException();
-            }
-            public void Signal() => throw new NotImplementedException();
-
-            
-        }
     }
 }

tests/Avalonia.Base.UnitTests/DispatcherTests.Exception.cs

@@ -1,43 +1,76 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Controls.Platform;
 using Avalonia.Threading;
+using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Base.UnitTests;
 
 // Some of these exceptions are based from https://github.com/dotnet/wpf-test/blob/05797008bb4975ceeb71be36c47f01688f535d53/src/Test/ElementServices/FeatureTests/Untrusted/Dispatcher/UnhandledExceptionTest.cs#L30
-public partial class DispatcherTests
+public partial class DispatcherTests : ScopedTestBase
 {
     private const string ExpectedExceptionText = "Exception thrown inside Dispatcher.Invoke / Dispatcher.BeginInvoke.";
 
     private int _numberOfHandlerOnUnhandledEventInvoked;
     private int _numberOfHandlerOnUnhandledEventFilterInvoked;
+    private Dispatcher _uiThread;
 
     public DispatcherTests()
     {
         _numberOfHandlerOnUnhandledEventInvoked = 0;
         _numberOfHandlerOnUnhandledEventFilterInvoked = 0;
+
+        VerifyDispatcherSanity();
+        _uiThread = Dispatcher.CurrentDispatcher;
+    }
+
+    void VerifyDispatcherSanity()
+    {
+        // Verify that we are in a clear-ish state. Do this for every test to ensure that our reset procedure is working
+        Assert.Null(Dispatcher.FromThread(Thread.CurrentThread));
+        Assert.Null(Dispatcher.TryGetUIThread());
+
+        // The first (this) dispatcher becomes UI thread one
+        Assert.NotNull(Dispatcher.CurrentDispatcher);
+        Assert.Equal(Dispatcher.TryGetUIThread(), Dispatcher.CurrentDispatcher);
+        Assert.Equal(Dispatcher.UIThread, Dispatcher.CurrentDispatcher);
+
+        // Dispatcher.FromThread works
+        Assert.Equal(Dispatcher.CurrentDispatcher, Dispatcher.FromThread(Thread.CurrentThread));
+        Assert.Equal(Dispatcher.UIThread, Dispatcher.FromThread(Thread.CurrentThread));
     }
 
     [Fact]
-    public void DispatcherHandlesExceptionWithPost()
+    [SuppressMessage("Usage", "xUnit1031:Do not use blocking task operations in test method", Justification = "Tests the dispatcher itself")]
+    public void Different_Threads_Auto_Spawn_Dispatchers()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var disp = new Dispatcher(impl);
+        var dispatcher = Dispatcher.CurrentDispatcher;
+        ThreadRunHelper.RunOnDedicatedThread(() =>
+        {
+            Assert.Null(Dispatcher.FromThread(Thread.CurrentThread));
+            Assert.NotNull(Dispatcher.CurrentDispatcher);
+            Assert.NotEqual(dispatcher, Dispatcher.CurrentDispatcher);
+            Assert.Equal(Dispatcher.CurrentDispatcher, Dispatcher.FromThread(Thread.CurrentThread));
+        }).GetAwaiter().GetResult();
+    }
 
+    [Fact]
+    public void DispatcherHandlesExceptionWithPost()
+    {
         var handled = false;
         var executed = false;
-        disp.UnhandledException += (sender, args) =>
+        _uiThread.UnhandledException += (sender, args) =>
         {
             handled = true;
             args.Handled = true;
         };
-        disp.Post(() => ThrowAnException());
-        disp.Post(() => executed = true);
+        _uiThread.Post(() => ThrowAnException());
+        _uiThread.Post(() => executed = true);
 
-        disp.RunJobs(null, TestContext.Current.CancellationToken);
+        _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         
         Assert.True(handled);
         Assert.True(executed);
@@ -46,14 +79,11 @@ public partial class DispatcherTests
     [Fact]
     public void SyncContextExceptionCanBeHandledWithPost()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var disp = new Dispatcher(impl);
-
-        var syncContext = disp.GetContextWithPriority(DispatcherPriority.Background);
+        var syncContext = _uiThread.GetContextWithPriority(DispatcherPriority.Background);
 
         var handled = false;
         var executed = false;
-        disp.UnhandledException += (sender, args) =>
+        _uiThread.UnhandledException += (sender, args) =>
         {
             handled = true;
             args.Handled = true;
@@ -62,7 +92,7 @@ public partial class DispatcherTests
         syncContext.Post(_ => ThrowAnException(), null);
         syncContext.Post(_ => executed = true, null);
 
-        disp.RunJobs(null, TestContext.Current.CancellationToken);
+        _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
 
         Assert.True(handled);
         Assert.True(executed);
@@ -71,24 +101,22 @@ public partial class DispatcherTests
     [Fact]
     public void CanRemoveDispatcherExceptionHandler()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
         var caughtCorrectException = false;
 
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionNotHandled;
 
-        dispatcher.UnhandledExceptionFilter -=
+        _uiThread.UnhandledExceptionFilter -=
             HandlerOnUnhandledExceptionFilterRequestCatch;
-        dispatcher.UnhandledException -=
+        _uiThread.UnhandledException -=
             HandlerOnUnhandledExceptionNotHandled;
 
         try
         {
-            dispatcher.Post(ThrowAnException, DispatcherPriority.Normal);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Post(ThrowAnException, DispatcherPriority.Normal);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception e)
         {
@@ -103,19 +131,16 @@ public partial class DispatcherTests
     [Fact]
     public void CanHandleExceptionWithUnhandledException()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionHandled;
         var caughtCorrectException = true;
         try
         {
-            dispatcher.Post(ThrowAnException, DispatcherPriority.Normal);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Post(ThrowAnException, DispatcherPriority.Normal);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception)
         {
@@ -131,20 +156,17 @@ public partial class DispatcherTests
     [Fact]
     public void InvokeMethodDoesntTriggerUnhandledException()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionHandled;
         var caughtCorrectException = false;
         try
         {
             // Since both Invoke and InvokeAsync can throw exception, there is no need to pass them to the UnhandledException.
-            dispatcher.Invoke(ThrowAnException, DispatcherPriority.Normal, TestContext.Current.CancellationToken);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Invoke(ThrowAnException, DispatcherPriority.Normal, TestContext.Current.CancellationToken);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception e)
         {
@@ -160,21 +182,18 @@ public partial class DispatcherTests
     [Fact]
     public void InvokeAsyncMethodDoesntTriggerUnhandledException()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionHandled;
         var caughtCorrectException = false;
         try
         {
             // Since both Invoke and InvokeAsync can throw exception, there is no need to pass them to the UnhandledException.
-            var op = dispatcher.InvokeAsync(ThrowAnException, DispatcherPriority.Normal, TestContext.Current.CancellationToken);
+            var op = _uiThread.InvokeAsync(ThrowAnException, DispatcherPriority.Normal, TestContext.Current.CancellationToken);
             op.Wait();
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception e)
         {
@@ -190,19 +209,16 @@ public partial class DispatcherTests
     [Fact]
     public void CanRethrowExceptionWithUnhandledException()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionNotHandled;
         var caughtCorrectException = false;
         try
         {
-            dispatcher.Post(ThrowAnException, DispatcherPriority.Normal);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Post(ThrowAnException, DispatcherPriority.Normal);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception e)
         {
@@ -217,23 +233,20 @@ public partial class DispatcherTests
     [Fact]
     public void MultipleUnhandledExceptionFilterCannotResetRequestCatchFlag()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterNotRequestCatch;
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionNotHandled;
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionHandled;
         var caughtCorrectException = false;
         try
         {
-            dispatcher.Post(ThrowAnException, DispatcherPriority.Normal);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Post(ThrowAnException, DispatcherPriority.Normal);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception e)
         {
@@ -248,22 +261,19 @@ public partial class DispatcherTests
     [Fact]
     public void MultipleUnhandledExceptionCannotResetHandleFlag()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterRequestCatch;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionHandled;
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionNotHandled;
         var caughtCorrectException = true;
         
         try
         {
-            dispatcher.Post(ThrowAnException, DispatcherPriority.Normal);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Post(ThrowAnException, DispatcherPriority.Normal);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception)
         {
@@ -279,19 +289,16 @@ public partial class DispatcherTests
     [Fact]
     public void CanPushFrameAndShutdownDispatcherFromUnhandledException()
     {
-        var impl = new ManagedDispatcherImpl(null);
-        var dispatcher = new Dispatcher(impl);
-        
-        dispatcher.UnhandledExceptionFilter +=
+        _uiThread.UnhandledExceptionFilter +=
             HandlerOnUnhandledExceptionFilterNotRequestCatchPushFrame;
         
-        dispatcher.UnhandledException +=
+        _uiThread.UnhandledException +=
             HandlerOnUnhandledExceptionHandledPushFrame;
         var caughtCorrectException = false;
         try
         {
-            dispatcher.Post(ThrowAnException, DispatcherPriority.Normal);
-            dispatcher.RunJobs(null, TestContext.Current.CancellationToken);
+            _uiThread.Post(ThrowAnException, DispatcherPriority.Normal);
+            _uiThread.RunJobs(null, TestContext.Current.CancellationToken);
         }
         catch (Exception e)
         {

tests/Avalonia.Base.UnitTests/DispatcherTests.cs

@@ -8,6 +8,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Controls.Platform;
 using Avalonia.Threading;
+using Avalonia.UnitTests;
 using Avalonia.Utilities;
 using Xunit;
 namespace Avalonia.Base.UnitTests;
@@ -121,11 +122,11 @@ public partial class DispatcherTests
     public void DispatcherExecutesJobsAccordingToPriority()
     {
         var impl = new SimpleDispatcherImpl();
-        var disp = new Dispatcher(impl);
+        Dispatcher.InitializeUIThreadDispatcher(impl);
         var actions = new List<string>();
-        disp.Post(()=>actions.Add("Background"), DispatcherPriority.Background);
-        disp.Post(()=>actions.Add("Render"), DispatcherPriority.Render);
-        disp.Post(()=>actions.Add("Input"), DispatcherPriority.Input);
+        _uiThread.Post(()=>actions.Add("Background"), DispatcherPriority.Background);
+        _uiThread.Post(()=>actions.Add("Render"), DispatcherPriority.Render);
+        _uiThread.Post(()=>actions.Add("Input"), DispatcherPriority.Input);
         Assert.True(impl.AskedForSignal);
         impl.ExecuteSignal();
         Assert.Equal(new[] { "Render", "Input", "Background" }, actions);
@@ -135,12 +136,11 @@ public partial class DispatcherTests
     public void DispatcherPreservesOrderWhenChangingPriority()
     {
         var impl = new SimpleDispatcherImpl();
-        var disp = new Dispatcher(impl);
+        Dispatcher.InitializeUIThreadDispatcher(impl);
         var actions = new List<string>();
-        var toPromote = disp.InvokeAsync(()=>actions.Add("PromotedRender"), DispatcherPriority.Background, TestContext.Current.CancellationToken);
-        var toPromote2 = disp.InvokeAsync(()=>actions.Add("PromotedRender2"), DispatcherPriority.Input, TestContext.Current.CancellationToken);
-        disp.Post(() => actions.Add("Render"), DispatcherPriority.Render);
-
+        var toPromote = _uiThread.InvokeAsync(()=>actions.Add("PromotedRender"), DispatcherPriority.Background, TestContext.Current.CancellationToken);
+        var toPromote2 = _uiThread.InvokeAsync(()=>actions.Add("PromotedRender2"), DispatcherPriority.Input, TestContext.Current.CancellationToken);
+        _uiThread.Post(() => actions.Add("Render"), DispatcherPriority.Render);
         toPromote.Priority = DispatcherPriority.Render;
         toPromote2.Priority = DispatcherPriority.Render;
 
@@ -154,12 +154,13 @@ public partial class DispatcherTests
     public void DispatcherStopsItemProcessingWhenInteractivityDeadlineIsReached()
     {
         var impl = new SimpleDispatcherImpl();
-        var disp = new Dispatcher(impl);
+        Dispatcher.ResetForUnitTests();
+        _uiThread = new Dispatcher(impl);
         var actions = new List<int>();
         for (var c = 0; c < 10; c++)
         {
             var itemId = c;
-            disp.Post(() =>
+            _uiThread.Post(() =>
             {
                 actions.Add(itemId);
                 impl.Now += 20;
@@ -195,14 +196,17 @@ public partial class DispatcherTests
     [Fact]
     public void DispatcherStopsItemProcessingWhenInputIsPending()
     {
+        Dispatcher.ResetForUnitTests();
+
         var impl = new SimpleDispatcherImpl();
         impl.TestInputPending = true;
-        var disp = new Dispatcher(impl);
+        _uiThread = new Dispatcher(impl);
+
         var actions = new List<int>();
         for (var c = 0; c < 10; c++)
         {
             var itemId = c;
-            disp.Post(() =>
+            _uiThread.Post(() =>
             {
                 actions.Add(itemId);
                 if (itemId == 0 || itemId == 3 || itemId == 7)
@@ -249,10 +253,10 @@ public partial class DispatcherTests
     public void CanWaitForDispatcherOperationFromTheSameThread(bool controlled, bool foreground)
     {
         var impl = controlled ? new SimpleControlledDispatcherImpl() : new SimpleDispatcherImpl();
-        var disp = new Dispatcher(impl);
+        Dispatcher.InitializeUIThreadDispatcher(impl);
         bool finished = false;
 
-        disp.InvokeAsync(() => finished = true,
+        _uiThread.InvokeAsync(() => finished = true,
             foreground ? DispatcherPriority.Default : DispatcherPriority.Background).Wait();
 
         Assert.True(finished);
@@ -268,7 +272,6 @@ public partial class DispatcherTests
         public DispatcherServices(IDispatcherImpl impl)
         {
             _scope = AvaloniaLocator.EnterScope();
-            AvaloniaLocator.CurrentMutable.Bind<IDispatcherImpl>().ToConstant(impl);
             Dispatcher.ResetForUnitTests();
             SynchronizationContext.SetSynchronizationContext(null);
         }

tests/Avalonia.Base.UnitTests/Input/MouseDeviceTests.cs

@@ -18,17 +18,13 @@ namespace Avalonia.Base.UnitTests.Input
         {
             using var scope = AvaloniaLocator.EnterScope();
             var settingsMock = new Mock<IPlatformSettings>();
-            var dispatcherMock = new Mock<IDispatcherImpl>();
-
-            dispatcherMock.Setup(x => x.CurrentThreadIsLoopThread).Returns(true);
-
+            
             AvaloniaLocator.CurrentMutable.BindToSelf(this)
                 .Bind<IPlatformSettings>().ToConstant(settingsMock.Object);
 
             using var app = UnitTestApplication.Start(
                 new TestServices(
-                    inputManager: new InputManager(),
-                    dispatcherImpl: dispatcherMock.Object));
+                    inputManager: new InputManager()));
 
             var renderer = new Mock<IHitTester>();
             var device = new MouseDevice();

tests/Avalonia.Base.UnitTests/Input/TouchDeviceTests.cs

@@ -213,7 +213,7 @@ namespace Avalonia.Input.UnitTests
         private IDisposable UnitTestApp(TimeSpan doubleClickTime = new TimeSpan())
         {
             var unitTestApp = UnitTestApplication.Start(
-                new TestServices(inputManager: new InputManager(), dispatcherImpl: Mock.Of<IDispatcherImpl>(x => x.CurrentThreadIsLoopThread == true)));
+                new TestServices(inputManager: new InputManager()));
             var iSettingsMock = new Mock<IPlatformSettings>();
             iSettingsMock.Setup(x => x.GetDoubleTapTime(It.IsAny<PointerType>())).Returns(doubleClickTime);
             iSettingsMock.Setup(x => x.GetDoubleTapSize(It.IsAny<PointerType>())).Returns(new Size(16, 16));

tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs

@@ -28,7 +28,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Should_Set_ExitCode_After_Shutdown()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: new ManagedDispatcherImpl(null))))
+            using (UnitTestApplication.Start(new TestServices()))
             using(var lifetime = new ClassicDesktopStyleApplicationLifetime())    
             {
                 lifetime.SetupCore(Array.Empty<string>());
@@ -326,7 +326,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Should_Allow_Canceling_Shutdown_Via_ShutdownRequested_Event()
         {
-            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: new ManagedDispatcherImpl(null))))
+            using (UnitTestApplication.Start(TestServices.StyledWindow.With()))
             using (var lifetime = new ClassicDesktopStyleApplicationLifetime())
             {
                 var lifetimeEvents = new Mock<IPlatformLifetimeEventsImpl>();
@@ -475,7 +475,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Shutdown_NotCancellable_By_Preventing_Window_Close()
         {
-            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
+            using (UnitTestApplication.Start(TestServices.StyledWindow.With()))
             using(var lifetime = new ClassicDesktopStyleApplicationLifetime())
             {
                 lifetime.SetupCore(Array.Empty<string>());

tests/Avalonia.Controls.UnitTests/Primitives/UniformGridTests.cs

@@ -1,7 +1,6 @@
-using System;
+using System;
 using Avalonia.Controls.Primitives;
 using Avalonia.UnitTests;
-using Avalonia.Utilities;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests.Primitives

tests/Avalonia.LeakTests/AvaloniaObjectTests.cs

@@ -149,7 +149,7 @@ namespace Avalonia.LeakTests
             }
 
             var weakTarget = SetupBinding();
-            
+
             CollectGarbage();
             Assert.False(weakTarget.IsAlive);
         }

tests/Avalonia.Markup.UnitTests/Data/BindingTests_Delay.cs

@@ -24,8 +24,9 @@ public class BindingTests_Delay : ScopedTestBase, IDisposable
     
     public BindingTests_Delay()
     {
+        _app = UnitTestApplication.Start(new(keyboardDevice: () => new KeyboardDevice()));
         _dispatcher = new ManualTimerDispatcher();
-        _app = UnitTestApplication.Start(new(dispatcherImpl: _dispatcher, keyboardDevice: () => new KeyboardDevice()));
+        _ = new Dispatcher(_dispatcher);
 
         _source = new BindingTests.Source { Foo = InitialFooValue };
         _target = new TextBox { DataContext = _source };

tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AttachedProperty.cs

@@ -4,11 +4,10 @@ using System.Reactive.Linq;
 using System.Threading.Tasks;
 using Avalonia.Diagnostics;
 using Avalonia.Data.Core;
-using Xunit;
-using Avalonia.Utilities;
-using Avalonia.Data.Core.ExpressionNodes;
-using Avalonia.UnitTests;
 using Avalonia.Data.Core.Parsers;
+using Avalonia.UnitTests;
+using Avalonia.Utilities;
+using Xunit;
 
 namespace Avalonia.Markup.UnitTests.Parsers
 {

tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AvaloniaProperty.cs

@@ -6,7 +6,6 @@ using Avalonia.Diagnostics;
 using Avalonia.Data.Core;
 using Xunit;
 using Avalonia.Utilities;
-using Avalonia.Data.Core.ExpressionNodes;
 using Avalonia.UnitTests;
 using Avalonia.Data.Core.Parsers;
 

tests/Avalonia.Markup.Xaml.UnitTests/Avalonia.Markup.Xaml.UnitTests.csproj

@@ -41,5 +41,15 @@
     </Compile>
     <Compile Include="../Shared/ScopedSanityCheck.cs"/>
   </ItemGroup>
+  <ItemGroup>
+    <PackageReference Update="xunit.runner.console" Version="2.9.2">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Update="xunit.runner.visualstudio" Version="2.8.2">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
   <Import Project="..\..\build\BuildTargets.targets" />
 </Project>

tests/Avalonia.RenderTests/TestRenderHelper.cs

@@ -28,16 +28,9 @@ namespace Avalonia.Skia.RenderTests;
 
 static class TestRenderHelper
 {
-    private static readonly TestDispatcherImpl s_dispatcherImpl =
-        new TestDispatcherImpl();
-
     static TestRenderHelper()
     {
         SkiaPlatform.Initialize();
-        AvaloniaLocator.CurrentMutable
-            .Bind<IDispatcherImpl>()
-            .ToConstant(s_dispatcherImpl);
-        
         AvaloniaLocator.CurrentMutable.Bind<IAssetLoader>().ToConstant(new StandardAssetLoader());
         AvaloniaLocator.CurrentMutable.Bind<ITextShaperImpl>().ToConstant(new HarfBuzzTextShaper());
     }
@@ -48,7 +41,7 @@ static class TestRenderHelper
         var dir = Path.GetDirectoryName(path);
         Assert.NotNull(dir);
 
-        if (!Directory.Exists(dir)) 
+        if (!Directory.Exists(dir))
             Directory.CreateDirectory(dir);
         
         var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
@@ -110,13 +103,14 @@ static class TestRenderHelper
 
     public static void BeginTest()
     {
-        s_dispatcherImpl.MainThread = Thread.CurrentThread;
+        Dispatcher.ResetBeforeUnitTests();
     }
 
     public static void EndTest()
     {
         if (Dispatcher.UIThread.CheckAccess()) 
             Dispatcher.UIThread.RunJobs();
+        Dispatcher.ResetForUnitTests();
     }
     
     public static string GetTestsDirectory()
@@ -131,28 +125,6 @@ static class TestRenderHelper
         Assert.NotNull(path);
         return path;
     }
-    
-    private class TestDispatcherImpl : IDispatcherImpl
-    {
-        public bool CurrentThreadIsLoopThread => MainThread?.ManagedThreadId == Thread.CurrentThread.ManagedThreadId;
-
-        public Thread? MainThread { get; set; }
-
-        public event Action? Signaled { add { } remove { } }
-        public event Action? Timer { add { } remove { } }
-
-        public void Signal()
-        {
-            // No-op
-        }
-
-        public long Now => 0;
-
-        public void UpdateTimer(long? dueTimeInMs)
-        {
-            // No-op
-        }
-    }
 
     public static void AssertCompareImages(string actualPath, string expectedPath)
     {

tests/Avalonia.UnitTests/TestServices.cs

@@ -15,34 +15,32 @@ namespace Avalonia.UnitTests
 {
     public class TestServices
     {
-        public static readonly TestServices StyledWindow = new TestServices(
+        public static TestServices StyledWindow => new TestServices(
             assetLoader: new StandardAssetLoader(),
             platform: new StandardRuntimePlatform(),
             renderInterface: new HeadlessPlatformRenderInterface(),
             standardCursorFactory: new HeadlessCursorFactoryStub(),
             theme: () => CreateSimpleTheme(),
-            dispatcherImpl: new NullDispatcherImpl(),
             fontManagerImpl: new TestFontManager(),
             textShaperImpl: new HarfBuzzTextShaper(),
             windowingPlatform: new MockWindowingPlatform());
 
-        public static readonly TestServices MockPlatformRenderInterface = new TestServices(
+        public static TestServices MockPlatformRenderInterface => new TestServices(
             assetLoader: new StandardAssetLoader(),
             renderInterface: new HeadlessPlatformRenderInterface(),
             fontManagerImpl: new TestFontManager(),
             textShaperImpl: new HarfBuzzTextShaper());
 
-        public static readonly TestServices MockPlatformWrapper = new TestServices(
+        public static TestServices MockPlatformWrapper => new TestServices(
             platform: Mock.Of<IRuntimePlatform>());
 
-        public static readonly TestServices MockThreadingInterface = new TestServices(
-            dispatcherImpl: new NullDispatcherImpl(),
+        public static TestServices MockThreadingInterface => new TestServices(
             assetLoader: new StandardAssetLoader());
 
-        public static readonly TestServices MockWindowingPlatform = new TestServices(
+        public static TestServices MockWindowingPlatform => new TestServices(
             windowingPlatform: new MockWindowingPlatform());
 
-        public static readonly TestServices RealFocus = new TestServices(
+        public static TestServices RealFocus => new TestServices(
             keyboardDevice: () => new KeyboardDevice(),
             keyboardNavigation: () => new KeyboardNavigationHandler(),
             inputManager: new InputManager(),
@@ -51,7 +49,7 @@ namespace Avalonia.UnitTests
             fontManagerImpl: new TestFontManager(),
             textShaperImpl: new HarfBuzzTextShaper());
 
-        public static readonly TestServices FocusableWindow = new TestServices(
+        public static TestServices FocusableWindow => new TestServices(
             keyboardDevice: () => new KeyboardDevice(),
             keyboardNavigation: () => new KeyboardNavigationHandler(),
             inputManager: new InputManager(),
@@ -60,12 +58,11 @@ namespace Avalonia.UnitTests
             renderInterface: new HeadlessPlatformRenderInterface(),
             standardCursorFactory: new HeadlessCursorFactoryStub(),
             theme: () => CreateSimpleTheme(),
-            dispatcherImpl: new NullDispatcherImpl(),
             fontManagerImpl: new TestFontManager(),
             textShaperImpl: new HarfBuzzTextShaper(),
             windowingPlatform: new MockWindowingPlatform());
 
-        public static readonly TestServices TextServices = new TestServices(
+        public static TestServices TextServices => new TestServices(
             assetLoader: new StandardAssetLoader(),
             renderInterface: new HeadlessPlatformRenderInterface(),
             fontManagerImpl: new TestFontManager(),
@@ -82,7 +79,6 @@ namespace Avalonia.UnitTests
             IPlatformRenderInterface? renderInterface = null,
             ICursorFactory? standardCursorFactory = null,
             Func<IStyle>? theme = null,
-            IDispatcherImpl? dispatcherImpl = null,
             IFontManagerImpl? fontManagerImpl = null,
             ITextShaperImpl? textShaperImpl = null,
             IWindowImpl? windowImpl = null,
@@ -102,7 +98,6 @@ namespace Avalonia.UnitTests
             TextShaperImpl = textShaperImpl;
             StandardCursorFactory = standardCursorFactory;
             Theme = theme;
-            DispatcherImpl = dispatcherImpl;
             WindowImpl = windowImpl;
             WindowingPlatform = windowingPlatform;
         }
@@ -120,7 +115,6 @@ namespace Avalonia.UnitTests
         public ITextShaperImpl? TextShaperImpl { get; }
         public ICursorFactory? StandardCursorFactory { get; }
         public Func<IStyle>? Theme { get; }
-        public IDispatcherImpl? DispatcherImpl { get; }
         public IWindowImpl? WindowImpl { get; }
         public IWindowingPlatform? WindowingPlatform { get; }
 
@@ -138,7 +132,6 @@ namespace Avalonia.UnitTests
             IScheduler? scheduler = null,
             ICursorFactory? standardCursorFactory = null,
             Func<IStyle>? theme = null,
-            IDispatcherImpl? dispatcherImpl = null,
             IFontManagerImpl? fontManagerImpl = null,
             ITextShaperImpl? textShaperImpl = null,
             IWindowImpl? windowImpl = null,
@@ -158,7 +151,6 @@ namespace Avalonia.UnitTests
                 textShaperImpl: textShaperImpl ?? TextShaperImpl,
                 standardCursorFactory: standardCursorFactory ?? StandardCursorFactory,
                 theme: theme ?? Theme,
-                dispatcherImpl: dispatcherImpl ?? DispatcherImpl,
                 windowingPlatform: windowingPlatform ?? WindowingPlatform,
                 windowImpl: windowImpl ?? WindowImpl);
         }

tests/Avalonia.UnitTests/ThreadRunHelper.cs

@@ -1,5 +1,3 @@
-#nullable enable
-
 using System;
 using System.Threading;
 using System.Threading.Tasks;

tests/Avalonia.UnitTests/UnitTestApplication.cs

@@ -52,6 +52,7 @@ namespace Avalonia.UnitTests
 
                 (AvaloniaLocator.Current.GetService<IToolTipService>() as ToolTipService)?.Dispose();
                 (AvaloniaLocator.Current.GetService<FontManager>() as IDisposable)?.Dispose();
+                (AvaloniaLocator.Current.GetService<IInputManager>() as IDisposable)?.Dispose();
 
                 Dispatcher.ResetForUnitTests();
                 scope.Dispose();
@@ -84,7 +85,6 @@ namespace Avalonia.UnitTests
                 .Bind<IPlatformRenderInterface?>().ToConstant(Services.RenderInterface)
                 .Bind<IFontManagerImpl?>().ToConstant(Services.FontManagerImpl)
                 .Bind<ITextShaperImpl?>().ToConstant(Services.TextShaperImpl)
-                .Bind<IDispatcherImpl?>().ToConstant(Services.DispatcherImpl)
                 .Bind<ICursorFactory?>().ToConstant(Services.StandardCursorFactory)
                 .Bind<IWindowingPlatform?>().ToConstant(Services.WindowingPlatform)
                 .Bind<PlatformHotkeyConfiguration>().ToSingleton<PlatformHotkeyConfiguration>()