Merge pull request #3279 from ahopper/perf-reduce-allocation-in-lightweightobservablebase

Reduce calls to ToArray in LightweightObservableBase PublishNext

src/Avalonia.Base/Reactive/LightweightObservableBase.cs

@@ -116,20 +116,33 @@ namespace Avalonia.Reactive
         {
             if (Volatile.Read(ref _observers) != null)
             {
-                IObserver<T>[] observers;
-
+                IObserver<T>[] observers = null;
+                IObserver<T> singleObserver = null;
                 lock (this)
                 {
                     if (_observers == null)
                     {
                         return;
                     }
-                    observers = _observers.ToArray();
+                    if (_observers.Count == 1)
+                    {
+                        singleObserver = _observers[0];
+                    }
+                    else
+                    {
+                        observers = _observers.ToArray();
+                    }
                 }
-
-                foreach (var observer in observers)
+                if (singleObserver != null)
                 {
-                    observer.OnNext(value);
+                    singleObserver.OnNext(value);
+                }
+                else
+                {
+                    foreach (var observer in observers)
+                    {
+                        observer.OnNext(value);
+                    }
                 }
             }
         }

tests/Avalonia.Benchmarks/Data/BindingsBenchmark.cs

@@ -19,6 +19,22 @@ namespace Avalonia.Benchmarks.Data
             instance.Bind(TestClass.IntValueProperty, binding);
         }
 
+        [Benchmark]
+        public void UpdateTwoWayBinding_Via_Binding()
+        {
+            var instance = new TestClass();
+
+            var binding = new Binding(nameof(TestClass.BoundValue), BindingMode.TwoWay)
+            {
+                Source = instance
+            };
+
+            instance.Bind(TestClass.IntValueProperty, binding);
+            for (int i = 0; i < 60; i++)
+            {
+                instance.IntValue = i;
+            }
+        }
         private class TestClass : AvaloniaObject
         {
             public static readonly StyledProperty<int> IntValueProperty =