Marshal bindings to UI thread.

src/Avalonia.Base/PropertyStore/BindingEntryBase.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Reactive.Disposables;
 using Avalonia.Data;
+using Avalonia.Threading;
 
 namespace Avalonia.PropertyStore
 {
@@ -116,26 +117,42 @@ namespace Avalonia.PropertyStore
 
         private void SetValue(BindingValue<TValue> value)
         {
-            if (Frame.Owner is null)
-                return;
+            static void Execute(BindingEntryBase<TValue, TSource> instance, BindingValue<TValue> value)
+            {
+                if (instance.Frame.Owner is null)
+                    return;
 
-            LoggingUtils.LogIfNecessary(Frame.Owner.Owner, Property, value);
+                LoggingUtils.LogIfNecessary(instance.Frame.Owner.Owner, instance.Property, value);
 
-            if (value.HasValue)
-            {
-                if (!_hasValue || !EqualityComparer<TValue>.Default.Equals(_value, value.Value))
+                if (value.HasValue)
+                {
+                    if (!instance._hasValue || !EqualityComparer<TValue>.Default.Equals(instance._value, value.Value))
+                    {
+                        instance._value = value.Value;
+                        instance._hasValue = true;
+                        if (instance._subscription is not null && instance._subscription != s_creatingQuiet)
+                            instance.Frame.Owner?.OnBindingValueChanged(instance, instance.Frame.Priority);
+                    }
+                }
+                else if (value.Type != BindingValueType.DoNothing)
                 {
-                    _value = value.Value;
-                    _hasValue = true;
-                    if (_subscription is not null && _subscription != s_creatingQuiet)
-                        Frame.Owner?.OnBindingValueChanged(this, Frame.Priority);
+                    instance.ClearValue();
+                    if (instance._subscription is not null && instance._subscription != s_creatingQuiet)
+                        instance.Frame.Owner?.OnBindingValueCleared(instance.Property, instance.Frame.Priority);
                 }
             }
-            else if (value.Type != BindingValueType.DoNothing)
+
+            if (Dispatcher.UIThread.CheckAccess())
             {
-                ClearValue();
-                if (_subscription is not null && _subscription != s_creatingQuiet)
-                    Frame.Owner?.OnBindingValueCleared(Property, Frame.Priority);
+                Execute(this, value);
+            }
+            else
+            {
+                // To avoid allocating closure in the outer scope we need to capture variables
+                // locally. This allows us to skip most of the allocations when on UI thread.
+                var instance = this;
+                var newValue = value;
+                Dispatcher.UIThread.Post(() => Execute(instance, newValue));
             }
         }
 

src/Avalonia.Base/PropertyStore/LocalValueBindingObserver.cs

@@ -1,5 +1,6 @@
 using System;
 using Avalonia.Data;
+using Avalonia.Threading;
 
 namespace Avalonia.PropertyStore
 {
@@ -40,20 +41,56 @@ namespace Avalonia.PropertyStore
 
         public void OnNext(T value)
         {
-            if (Property.ValidateValue?.Invoke(value) != false)
-                _owner.SetValue(Property, value, BindingPriority.LocalValue);
+            static void Execute(ValueStore owner, StyledPropertyBase<T> property, T value)
+            {
+                if (property.ValidateValue?.Invoke(value) != false)
+                    owner.SetValue(property, value, BindingPriority.LocalValue);
+                else
+                    owner.ClearLocalValue(property);
+            }
+
+            if (Dispatcher.UIThread.CheckAccess())
+            {
+                Execute(_owner, Property, value);
+            }
             else
-                _owner.ClearLocalValue(Property);
+            {
+                // To avoid allocating closure in the outer scope we need to capture variables
+                // locally. This allows us to skip most of the allocations when on UI thread.
+                var instance = _owner;
+                var property = Property;
+                var newValue = value;
+                Dispatcher.UIThread.Post(() => Execute(instance, property, newValue));
+            }
         }
 
         public void OnNext(BindingValue<T> value)
         {
-            LoggingUtils.LogIfNecessary(_owner.Owner, Property, value);
+            static void Execute(LocalValueBindingObserver<T> instance, BindingValue<T> value)
+            {
+                var owner = instance._owner;
+                var property = instance.Property;
+
+                LoggingUtils.LogIfNecessary(owner.Owner, property, value);
 
-            if (value.HasValue)
-                _owner.SetValue(Property, value.Value, BindingPriority.LocalValue);
-            else if (value.Type != BindingValueType.DataValidationError)
-                _owner.ClearLocalValue(Property);
+                if (value.HasValue)
+                    owner.SetValue(property, value.Value, BindingPriority.LocalValue);
+                else if (value.Type != BindingValueType.DataValidationError)
+                    owner.ClearLocalValue(property);
+            }
+
+            if (Dispatcher.UIThread.CheckAccess())
+            {
+                Execute(this, value);
+            }
+            else
+            {
+                // To avoid allocating closure in the outer scope we need to capture variables
+                // locally. This allows us to skip most of the allocations when on UI thread.
+                var instance = this;
+                var newValue = value;
+                Dispatcher.UIThread.Post(() => Execute(instance, newValue));
+            }
         }
     }
 }

src/Avalonia.Base/PropertyStore/LocalValueUntypedBindingObserver.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Security.Cryptography;
 using Avalonia.Data;
+using Avalonia.Threading;
 
 namespace Avalonia.PropertyStore
 {
@@ -34,28 +36,47 @@ namespace Avalonia.PropertyStore
 
         public void OnNext(object? value)
         {
-            if (value is BindingNotification n)
+            static void Execute(LocalValueUntypedBindingObserver<T> instance, object? value)
             {
-                value = n.Value;
-                LoggingUtils.LogIfNecessary(_owner.Owner, Property, n);
-            }
+                var owner = instance._owner;
+                var property = instance.Property;
 
-            if (value == AvaloniaProperty.UnsetValue)
-            {
-                _owner.ClearLocalValue(Property);
-            }
-            else if (value == BindingOperations.DoNothing)
-            {
-                // Do nothing!
+                if (value is BindingNotification n)
+                {
+                    value = n.Value;
+                    LoggingUtils.LogIfNecessary(owner.Owner, property, n);
+                }
+
+                if (value == AvaloniaProperty.UnsetValue)
+                {
+                    owner.ClearLocalValue(property);
+                }
+                else if (value == BindingOperations.DoNothing)
+                {
+                    // Do nothing!
+                }
+                else if (UntypedValueUtils.TryConvertAndValidate(property, value, out var typedValue))
+                {
+                    owner.SetValue(property, typedValue, BindingPriority.LocalValue);
+                }
+                else
+                {
+                    owner.ClearLocalValue(property);
+                    LoggingUtils.LogInvalidValue(owner.Owner, property, typeof(T), value);
+                }
             }
-            else if (UntypedValueUtils.TryConvertAndValidate(Property, value, out var typedValue))
+
+            if (Dispatcher.UIThread.CheckAccess())
             {
-                _owner.SetValue(Property, typedValue, BindingPriority.LocalValue);
+                Execute(this, value);
             }
-            else
+            else if (value != BindingOperations.DoNothing)
             {
-                _owner.ClearLocalValue(Property);
-                LoggingUtils.LogInvalidValue(_owner.Owner, Property, typeof(T), value);
+                // To avoid allocating closure in the outer scope we need to capture variables
+                // locally. This allows us to skip most of the allocations when on UI thread.
+                var instance = this;
+                var newValue = value;
+                Dispatcher.UIThread.Post(() => Execute(instance, newValue));
             }
         }
     }