Try to respect DispatcherPriority when possible

src/Android/Avalonia.Android/AndroidThreadingInterface.cs

@@ -12,6 +12,7 @@ using Android.Runtime;
 using Android.Views;
 using Android.Widget;
 using Avalonia.Platform;
+using Avalonia.Threading;
 
 namespace Avalonia.Android
 {
@@ -78,13 +79,13 @@ namespace Avalonia.Android
 
         private void EnsureInvokeOnMainThread(Action action) => _handler.Post(action);
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
-            EnsureInvokeOnMainThread(() => Signaled?.Invoke());
+            EnsureInvokeOnMainThread(() => Signaled?.Invoke(null));
         }
 
         public bool CurrentThreadIsLoopThread => Looper.MainLooper.Thread.Equals(Java.Lang.Thread.CurrentThread());
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
     }
 }
  

src/Avalonia.Base/Platform/IPlatformThreadingInterface.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Threading;
+using Avalonia.Threading;
 
 namespace Avalonia.Platform
 {
@@ -21,10 +22,10 @@ namespace Avalonia.Platform
         /// <returns>An <see cref="IDisposable"/> used to stop the timer.</returns>
         IDisposable StartTimer(TimeSpan interval, Action tick);
 
-        void Signal();
+        void Signal(DispatcherPriority priority);
 
         bool CurrentThreadIsLoopThread { get; }
 
-        event Action Signaled;
+        event Action<DispatcherPriority?> Signaled;
     }
 }

src/Avalonia.Base/Threading/AvaloniaSynchronizationContext.cs

@@ -36,7 +36,7 @@ namespace Avalonia.Threading
         /// <inheritdoc/>
         public override void Post(SendOrPostCallback d, object state)
         {
-           Dispatcher.UIThread.InvokeAsync(() => d(state));
+           Dispatcher.UIThread.InvokeAsync(() => d(state), DispatcherPriority.Send);
         }
 
         /// <inheritdoc/>
@@ -45,7 +45,7 @@ namespace Avalonia.Threading
             if (Dispatcher.UIThread.CheckAccess())
                 d(state);
             else
-                Dispatcher.UIThread.InvokeTaskAsync(() => d(state)).Wait();
+                Dispatcher.UIThread.InvokeTaskAsync(() => d(state), DispatcherPriority.Send).Wait();
         }
     }
 }

src/Avalonia.Base/Threading/Dispatcher.cs

@@ -60,7 +60,7 @@ namespace Avalonia.Threading
         public void MainLoop(CancellationToken cancellationToken)
         {
             var platform = AvaloniaLocator.Current.GetService<IPlatformThreadingInterface>();
-            cancellationToken.Register(platform.Signal);
+            cancellationToken.Register(() => platform.Signal(DispatcherPriority.Send));
             platform.RunLoop(cancellationToken);
         }
 
@@ -69,7 +69,7 @@ namespace Avalonia.Threading
         /// </summary>
         public void RunJobs()
         {
-            _jobRunner?.RunJobs();
+            _jobRunner?.RunJobs(null);
         }
 
         /// <inheritdoc/>

src/Avalonia.Base/Threading/DispatcherPriority.cs

@@ -9,11 +9,7 @@ namespace Avalonia.Threading
     // TODO: These are copied from WPF - many won't apply to Avalonia.
     public enum DispatcherPriority
     {
-        /// <summary>
-        /// The job will not be processed.
-        /// </summary>
-        Inactive = 0,
-
+        MinValue = 1,
         /// <summary>
         /// The job will be processed when the system is idle.
         /// </summary>
@@ -63,5 +59,6 @@ namespace Avalonia.Threading
         /// The job will be processed before other asynchronous operations.
         /// </summary>
         Send = 10,
+        MaxValue = 10
     }
 }

src/Avalonia.Base/Threading/JobRunner.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 using Avalonia.Platform;
 
@@ -13,29 +14,45 @@ namespace Avalonia.Threading
     /// </summary>
     internal class JobRunner
     {
-        private readonly Queue<Job> _queue = new Queue<Job>();
+
+
         private IPlatformThreadingInterface _platform;
 
+        private Queue<Job>[] _queues = Enumerable.Range(0, (int) DispatcherPriority.MaxValue + 1)
+            .Select(_ => new Queue<Job>()).ToArray();
+
         public JobRunner(IPlatformThreadingInterface platform)
         {
             _platform = platform;
         }
 
+        Job GetNextJob(DispatcherPriority minimumPriority)
+        {
+            for (int c = (int) DispatcherPriority.MaxValue; c >= (int) minimumPriority; c--)
+            {
+                var q = _queues[c];
+                lock (q)
+                {
+                    if (q.Count > 0)
+                        return q.Dequeue();
+                }
+            }
+            return null;
+        }
+
         /// <summary>
         /// Runs continuations pushed on the loop.
         /// </summary>
-        public void RunJobs()
+        /// <param name="priority">Priority to execute jobs for. Pass null if platform doesn't have internal priority system</param>
+        public void RunJobs(DispatcherPriority? priority)
         {
+            var minimumPriority = priority ?? DispatcherPriority.MinValue;
             while (true)
             {
-                Job job;
-
-                lock (_queue)
-                {
-                    if (_queue.Count == 0)
-                        return;
-                    job = _queue.Dequeue();
-                }
+                var job = GetNextJob(minimumPriority);
+                if (job == null)
+                    return;
+                
 
                 if (job.TaskCompletionSource == null)
                 {
@@ -77,7 +94,6 @@ namespace Avalonia.Threading
         /// <param name="priority">The priority with which to invoke the method.</param>
         internal void Post(Action action, DispatcherPriority priority)
         {
-            // TODO: Respect priority.
             AddJob(new Job(action, priority, true));
         }
 
@@ -92,13 +108,14 @@ namespace Avalonia.Threading
         private void AddJob(Job job)
         {
             var needWake = false;
-            lock (_queue)
+            var queue = _queues[(int) job.Priority];
+            lock (queue)
             {
-                needWake = _queue.Count == 0;
-                _queue.Enqueue(job);
+                needWake = queue.Count == 0;
+                queue.Enqueue(job);
             }
             if (needWake)
-                _platform?.Signal();
+                _platform?.Signal(job.Priority);
         }
 
         /// <summary>

src/Avalonia.Base/Threading/SingleThreadDispatcher.cs

@@ -1,60 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
-using Avalonia.Platform;
-
-namespace Avalonia.Threading
-{
-    public class SingleThreadDispatcher : Dispatcher
-    {
-        class ThreadingInterface : IPlatformThreadingInterface
-        {
-            private readonly AutoResetEvent _evnt = new AutoResetEvent(false);
-            private readonly JobRunner _timerJobRunner;
-
-            public ThreadingInterface()
-            {
-                _timerJobRunner = new JobRunner(this);
-            }
-
-            public void RunLoop(CancellationToken cancellationToken)
-            {
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    _evnt.WaitOne();
-                    if (cancellationToken.IsCancellationRequested)
-                        return;
-                    Signaled?.Invoke();
-                    _timerJobRunner.RunJobs();
-                }
-            }
-
-            public IDisposable StartTimer(TimeSpan interval, Action tick)
-                => AvaloniaLocator.Current.GetService<IRuntimePlatform>().StartSystemTimer(interval,
-                    () => _timerJobRunner.Post(tick, DispatcherPriority.Normal));
-
-            public void Signal() => _evnt.Set();
-            //TODO: Actually perform a check
-            public bool CurrentThreadIsLoopThread => true;
-
-            public event Action Signaled;
-        }
-
-        public SingleThreadDispatcher() : base(new ThreadingInterface())
-        {
-        }
-
-        public static Dispatcher StartNew(CancellationToken token)
-        {
-            var dispatcher = new SingleThreadDispatcher();
-            AvaloniaLocator.Current.GetService<IRuntimePlatform>().PostThreadPoolItem(() =>
-            {
-                dispatcher.MainLoop(token);
-            });
-            return dispatcher;
-        }
-    }
-}

src/Avalonia.Controls/Primitives/Track.cs

@@ -165,7 +165,7 @@ namespace Avalonia.Controls.Primitives
 
                 if (increaseButton != null)
                 {
-                    increaseButton.Arrange(new Rect(0, firstHeight + thumbHeight, finalSize.Width, remaining - firstHeight));
+                    increaseButton.Arrange(new Rect(0, firstHeight + thumbHeight, finalSize.Width, Math.Max(remaining - firstHeight, 0)));
                 }
             }
 

src/Gtk/Avalonia.Gtk/GtkPlatform.cs

@@ -9,6 +9,7 @@ using Avalonia.Input.Platform;
 using Avalonia.Input;
 using Avalonia.Platform;
 using Avalonia.Controls;
+using Avalonia.Threading;
 
 namespace Avalonia
 {
@@ -91,14 +92,14 @@ namespace Avalonia.Gtk
 
 
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
-            Gtk.Application.Invoke(delegate { Signaled?.Invoke(); });
+            Gtk.Application.Invoke(delegate { Signaled?.Invoke(null); });
         }
 
         public bool CurrentThreadIsLoopThread => Thread.CurrentThread == _uiThread;
 
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
         public IWindowImpl CreateWindow()
         {
             return new WindowImpl();

src/Gtk/Avalonia.Gtk3/Avalonia.Gtk3.csproj

@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-    <EnableDefaultCompileItems>False</EnableDefaultCompileItems>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
@@ -28,33 +27,6 @@
     <Compile Include="..\Avalonia.Gtk\KeyTransform.cs">
       <Link>KeyTransform.cs</Link>
     </Compile>
-    <Compile Include="Interop\CairoSurface.cs" />
-    <Compile Include="ClipboardImpl.cs" />
-    <Compile Include="CursorFactory.cs" />
-    <Compile Include="FramebufferManager.cs" />
-    <Compile Include="GdkCursor.cs" />
-    <Compile Include="GdkKey.cs" />
-    <Compile Include="Gtk3Platform.cs" />
-    <Compile Include="Interop\GException.cs" />
-    <Compile Include="Interop\GObject.cs" />
-    <Compile Include="Interop\ICustomGtk3NativeLibraryResolver.cs" />
-    <Compile Include="Interop\DynLoader.cs" />
-    <Compile Include="Interop\GlibTimeout.cs" />
-    <Compile Include="Interop\Native.cs" />
-    <Compile Include="Interop\NativeException.cs" />
-    <Compile Include="Interop\Pixbuf.cs" />
-    <Compile Include="Interop\Resolver.cs" />
-    <Compile Include="Interop\Signal.cs" />
-    <Compile Include="ImageSurfaceFramebuffer.cs" />
-    <Compile Include="PlatformIconLoader.cs" />
-    <Compile Include="PopupImpl.cs" />
-    <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="SystemDialogs.cs" />
-    <Compile Include="WindowBaseImpl.cs" />
-    <Compile Include="Interop\Utf8Buffer.cs" />
-    <Compile Include="WindowImpl.cs" />
-    <Compile Include="ScreenImpl.cs" />
-    <Compile Include="GtkScreen.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\Avalonia.Base\Avalonia.Base.csproj" />

src/Gtk/Avalonia.Gtk3/Gtk3Platform.cs

@@ -12,6 +12,7 @@ using Avalonia.Input.Platform;
 using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.Gtk3;
+using Avalonia.Threading;
 
 namespace Avalonia.Gtk3
 {
@@ -68,27 +69,28 @@ namespace Avalonia.Gtk3
             return GlibTimeout.StarTimer((uint) interval.TotalMilliseconds, tick);
         }
 
-        private bool _signaled = false;
+        private bool[] _signaled = new bool[(int) DispatcherPriority.MaxValue + 1];
         object _lock = new object();
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
+            var idx = (int) prio;
             lock(_lock)
-                if (!_signaled)
+                if (!_signaled[idx])
                 {
-                    _signaled = true;
-                    GlibTimeout.Add(0, () =>
+                    _signaled[idx] = true;
+                    GlibTimeout.Add(GlibPriority.FromDispatcherPriority(prio), 0, () =>
                     {
                         lock (_lock)
                         {
-                            _signaled = false;
+                            _signaled[idx] = false;
                         }
-                        Signaled?.Invoke();
+                        Signaled?.Invoke(prio);
                         return false;
                     });
                 }
         }
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
 
 
         [ThreadStatic]

src/Gtk/Avalonia.Gtk3/Interop/GlibPriority.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Avalonia.Threading;
+
+namespace Avalonia.Gtk3.Interop
+{
+    static class GlibPriority
+    {
+        public static int High = -100;
+        public static int Default = 0;
+        public static int HighIdle = 100;
+        public static int GtkResize = HighIdle + 10;
+        public static int GtkPaint = HighIdle + 20;
+        public static int DefaultIdle = 200;
+        public static int Low = 300;
+        public static int GdkEvents = Default;
+        public static int GdkRedraw = HighIdle + 20;
+
+        public static int FromDispatcherPriority(DispatcherPriority prio)
+        {
+            if (prio == DispatcherPriority.Send)
+                return High;
+            if (prio == DispatcherPriority.Normal)
+                return Default - 4;
+            if (prio == DispatcherPriority.DataBind)
+                return Default - 3;
+            if (prio == DispatcherPriority.Render)
+                return Default -2;
+            if (prio == DispatcherPriority.Loaded)
+                return Default - 1;
+            if (prio == DispatcherPriority.Input)
+                return Default;
+            if (prio == DispatcherPriority.Background)
+                return DefaultIdle;
+            if (prio == DispatcherPriority.ContextIdle)
+                return DefaultIdle + 100;
+            if (prio == DispatcherPriority.ApplicationIdle)
+                return DefaultIdle + 200;
+            if (prio == DispatcherPriority.SystemIdle)
+                return DefaultIdle + 200;
+            throw new ArgumentException("Unknown priority");
+
+        }
+    }
+}

src/Gtk/Avalonia.Gtk3/Interop/GlibTimeout.cs

@@ -30,7 +30,7 @@ namespace Avalonia.Gtk3.Interop
         }
 
 
-        public static void Add(uint interval, Func<bool> callback)
+        public static void Add(int priority, uint interval, Func<bool> callback)
         {
             var handle = GCHandle.Alloc(callback);
             Native.GTimeoutAdd(interval, PinnedHandler, GCHandle.ToIntPtr(handle));
@@ -49,7 +49,7 @@ namespace Avalonia.Gtk3.Interop
         public static IDisposable StarTimer(uint interval, Action tick)
         {
             var timer = new Timer ();
-            GlibTimeout.Add(interval,
+            GlibTimeout.Add(101, interval,
                 () =>
                 {
                     if (timer.Stopped)

src/Gtk/Avalonia.Gtk3/Interop/Native.cs

@@ -236,6 +236,9 @@ namespace Avalonia.Gtk3.Interop
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gdk)]
             public delegate void gdk_window_begin_resize_drag(IntPtr window, WindowEdge edge, gint button, gint root_x, gint root_y, guint32 timestamp);
 
+            [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gdk)]
+            public delegate void gdk_window_process_updates(IntPtr window, bool updateChildren);
+
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Gdk)]
             public delegate void gdk_event_request_motions(IntPtr ev);
 
@@ -287,7 +290,10 @@ namespace Avalonia.Gtk3.Interop
             
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Glib)]
             public delegate ulong g_timeout_add(uint interval, timeout_callback callback, IntPtr data);
-            
+
+            [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Glib)]
+            public delegate ulong g_timeout_add_full(int prio, uint interval, timeout_callback callback, IntPtr data, IntPtr destroy);
+
             [UnmanagedFunctionPointer(CallingConvention.Cdecl), GtkImport(GtkDll.Glib)]
             public delegate ulong g_free(IntPtr data);
             
@@ -366,6 +372,7 @@ namespace Avalonia.Gtk3.Interop
         public static D.g_signal_connect_object GSignalConnectObject;
         public static D.g_signal_handler_disconnect GSignalHandlerDisconnect;
         public static D.g_timeout_add GTimeoutAdd;
+        public static D.g_timeout_add_full GTimeoutAddFull;
         public static D.g_free GFree;
         public static D.g_slist_free GSlistFree;
         public static D.g_memory_input_stream_new_from_data GMemoryInputStreamNewFromData;
@@ -398,6 +405,7 @@ namespace Avalonia.Gtk3.Interop
         public static D.gdk_window_begin_move_drag GdkWindowBeginMoveDrag;
         public static D.gdk_window_begin_resize_drag GdkWindowBeginResizeDrag;
         public static D.gdk_event_request_motions GdkEventRequestMotions;
+        public static D.gdk_window_process_updates GdkWindowProcessUpdates;
 
         public static D.gdk_pixbuf_new_from_file GdkPixbufNewFromFile;
         public static D.gtk_icon_theme_get_default GtkIconThemeGetDefault;

src/Gtk/Avalonia.Gtk3/Interop/Resolver.cs

@@ -140,13 +140,11 @@ namespace Avalonia.Gtk3.Interop
             var nativeHandleNames = new[] { "gdk_win32_window_get_handle", "gdk_x11_window_get_xid", "gdk_quartz_window_get_nswindow" };
             foreach (var name in nativeHandleNames)
             {
-                try
-                {
-                    Native.GetNativeGdkWindowHandle = (Native.D.gdk_get_native_handle)Marshal
-                        .GetDelegateForFunctionPointer(loader.GetProcAddress(dlls[GtkDll.Gdk], name, false), typeof(Native.D.gdk_get_native_handle));
-                    break;
-                }
-                catch { }
+                var ptr = loader.GetProcAddress(dlls[GtkDll.Gdk], name, true);
+                if (ptr == IntPtr.Zero)
+                    continue;
+                Native.GetNativeGdkWindowHandle = (Native.D.gdk_get_native_handle) Marshal
+                    .GetDelegateForFunctionPointer(ptr, typeof(Native.D.gdk_get_native_handle));
             }
             if (Native.GetNativeGdkWindowHandle == null)
                 throw new Exception($"Unable to locate any of [{string.Join(", ", nativeHandleNames)}] in libgdk");

src/Gtk/Avalonia.Gtk3/WindowBaseImpl.cs

@@ -10,6 +10,7 @@ using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Platform;
 using Avalonia.Rendering;
+using Avalonia.Threading;
 
 namespace Avalonia.Gtk3
 {
@@ -25,6 +26,7 @@ namespace Avalonia.Gtk3
         private double _lastScaling;
         private uint _lastKbdEvent;
         private uint _lastSmoothScrollEvent;
+        private bool _hasDirtyRects;
 
         public WindowBaseImpl(GtkWindow gtkWidget)
         {
@@ -222,6 +224,7 @@ namespace Avalonia.Gtk3
 
         private bool OnDraw(IntPtr gtkwidget, IntPtr cairocontext, IntPtr userdata)
         {
+            _hasDirtyRects = false;
             CurrentCairoContext = cairocontext;
             Paint?.Invoke(new Rect(ClientSize));
             CurrentCairoContext = IntPtr.Zero;
@@ -271,6 +274,19 @@ namespace Avalonia.Gtk3
             if(GtkWidget.IsClosed)
                 return;
             Native.GtkWidgetQueueDrawArea(GtkWidget, (int)rect.X, (int)rect.Y, (int)rect.Width, (int)rect.Height);
+            if (!_hasDirtyRects)
+            {
+                _hasDirtyRects = true;
+                Dispatcher.UIThread.InvokeAsync(() =>
+                {
+                    if (GtkWidget.IsClosed)
+                        return;
+                    var window = Native.GtkWidgetGetWindow(GtkWidget);
+                    if (window == IntPtr.Zero)
+                        return;
+                    Native.GdkWindowProcessUpdates(window, false);
+                }, DispatcherPriority.Render);
+            }
         }
 
         public void SetInputRoot(IInputRoot inputRoot) => _inputRoot = inputRoot;

src/Linux/Avalonia.LinuxFramebuffer/PlatformThreadingInterface.cs

@@ -6,6 +6,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Platform;
 using Avalonia.Rendering;
+using Avalonia.Threading;
 
 namespace Avalonia.LinuxFramebuffer
 {
@@ -30,7 +31,7 @@ namespace Avalonia.LinuxFramebuffer
             while (true)
             {
                 if (0 == WaitHandle.WaitAny(handles))
-                    Signaled?.Invoke();
+                    Signaled?.Invoke(null);
                 else
                 {
                     while (true)
@@ -97,7 +98,7 @@ namespace Avalonia.LinuxFramebuffer
 
         }
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
             _signaled.Set();
         }
@@ -105,7 +106,7 @@ namespace Avalonia.LinuxFramebuffer
         [ThreadStatic] private static bool TlsCurrentThreadIsLoopThread;
 
         public bool CurrentThreadIsLoopThread => TlsCurrentThreadIsLoopThread;
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
         public event EventHandler<EventArgs> Tick;
 
     }

src/OSX/Avalonia.MonoMac/PlatformThreadingInterface.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Threading;
 using Avalonia.Platform;
+using Avalonia.Threading;
 using MonoMac.AppKit;
 using MonoMac.CoreGraphics;
 using MonoMac.Foundation;
@@ -13,12 +14,12 @@ namespace Avalonia.MonoMac
         public static PlatformThreadingInterface Instance { get; } = new PlatformThreadingInterface();
         public bool CurrentThreadIsLoopThread => NSThread.Current.IsMainThread;
 
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
 
         public IDisposable StartTimer(TimeSpan interval, Action tick)
             => NSTimer.CreateRepeatingScheduledTimer(interval, () => tick());
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
             lock (this)
             {
@@ -34,7 +35,7 @@ namespace Avalonia.MonoMac
                         return;
                     _signaled = false;
                 }
-                Signaled?.Invoke();
+                Signaled?.Invoke(null);
             });
         }
 

src/Windows/Avalonia.Win32/Win32Platform.cs

@@ -15,6 +15,7 @@ using Avalonia.Win32.Input;
 using Avalonia.Win32.Interop;
 using Avalonia.Controls;
 using Avalonia.Rendering;
+using Avalonia.Threading;
 #if NETSTANDARD
 using Win32Exception = Avalonia.Win32.NetStandard.AvaloniaWin32Exception;
 #else
@@ -137,7 +138,7 @@ namespace Avalonia.Win32
         private static readonly int SignalW = unchecked((int) 0xdeadbeaf);
         private static readonly int SignalL = unchecked((int)0x12345678);
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
             UnmanagedMethods.PostMessage(
                 _hwnd,
@@ -148,14 +149,14 @@ namespace Avalonia.Win32
 
         public bool CurrentThreadIsLoopThread => _uiThread == UnmanagedMethods.GetCurrentThreadId();
 
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
 
         [SuppressMessage("Microsoft.StyleCop.CSharp.NamingRules", "SA1305:FieldNamesMustNotUseHungarianNotation", Justification = "Using Win32 naming for consistency.")]
         private IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
         {
             if (msg == (int) UnmanagedMethods.WindowsMessage.WM_DISPATCH_WORK_ITEM && wParam.ToInt64() == SignalW && lParam.ToInt64() == SignalL)
             {
-                Signaled?.Invoke();
+                Signaled?.Invoke(null);
             }
             return UnmanagedMethods.DefWindowProc(hWnd, msg, wParam, lParam);
         }

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -16,6 +16,7 @@ using Avalonia.Win32.Input;
 using Avalonia.Win32.Interop;
 using static Avalonia.Win32.Interop.UnmanagedMethods;
 using Avalonia.Rendering;
+using Avalonia.Threading;
 #if NETSTANDARD
 using Win32Exception = Avalonia.Win32.NetStandard.AvaloniaWin32Exception;
 #endif

src/iOS/Avalonia.iOS/PlatformThreadingInterface.cs

@@ -9,6 +9,7 @@ using CoreAnimation;
 using Foundation;
 using Avalonia.Platform;
 using Avalonia.Shared.PlatformSupport;
+using Avalonia.Threading;
 
 namespace Avalonia.iOS
 {
@@ -18,7 +19,7 @@ namespace Avalonia.iOS
         public static PlatformThreadingInterface Instance { get; } = new PlatformThreadingInterface();
         public bool CurrentThreadIsLoopThread => NSThread.Current.IsMainThread;
         
-        public event Action Signaled;
+        public event Action<DispatcherPriority?> Signaled;
         public void RunLoop(CancellationToken cancellationToken)
         {
             //Mobile platforms are using external main loop
@@ -53,7 +54,7 @@ namespace Avalonia.iOS
         public IDisposable StartTimer(TimeSpan interval, Action tick)
             => NSTimer.CreateRepeatingScheduledTimer(interval, _ => tick());
 
-        public void Signal()
+        public void Signal(DispatcherPriority prio)
         {
             lock (this)
             {
@@ -65,7 +66,7 @@ namespace Avalonia.iOS
             {
                 lock (this)
                     _signaled = false;
-                Signaled?.Invoke();
+                Signaled?.Invoke(null);
             });
         }
     }

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_Threading.cs

@@ -6,6 +6,7 @@ using System.Reactive.Subjects;
 using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Platform;
+using Avalonia.Threading;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -147,14 +148,14 @@ namespace Avalonia.Base.UnitTests
 
             public bool CurrentThreadIsLoopThread { get; set; }
 
-            public event Action Signaled;
+            public event Action<DispatcherPriority?> Signaled;
 
             public void RunLoop(CancellationToken cancellationToken)
             {
                 throw new NotImplementedException();
             }
 
-            public void Signal()
+            public void Signal(DispatcherPriority prio)
             {
                 throw new NotImplementedException();
             }

tests/Avalonia.RenderTests/TestBase.cs

@@ -13,7 +13,7 @@ using Avalonia.Platform;
 using System.Threading.Tasks;
 using System;
 using System.Threading;
-
+using Avalonia.Threading;
 #if AVALONIA_CAIRO
 using Avalonia.Cairo;
 #elif AVALONIA_SKIA
@@ -155,14 +155,14 @@ namespace Avalonia.Direct2D1.RenderTests
 
             public Thread MainThread { get; set; }
 
-            public event Action Signaled;
+            public event Action<DispatcherPriority?> Signaled;
 
             public void RunLoop(CancellationToken cancellationToken)
             {
                 throw new NotImplementedException();
             }
 
-            public void Signal()
+            public void Signal(DispatcherPriority prio)
             {
                 throw new NotImplementedException();
             }