Avoid calling GetInvocationList on hot paths

src/Microsoft.DotNet.Wpf/src/PresentationCore/PresentationCore.csproj

@@ -335,6 +335,7 @@
     <Compile Include="System\Windows\Duration.cs" />
     <Compile Include="System\Windows\DurationConverter.cs" />
     <Compile Include="System\Windows\EventHandlersStore.cs" />
+    <Compile Include="System\Windows\EventHelper.cs" />
     <Compile Include="System\Windows\EventManager.cs" />
     <Compile Include="System\Windows\EventPrivateKey.cs" />
     <Compile Include="System\Windows\EventRoute.cs" />

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/EventHelper.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading;
+
+namespace System.Windows
+{
+    /// <summary>Provides helper methods for working with events and delegates.</summary>
+    internal static class EventHelper
+    {
+        /// <summary>Combines a delegate into an existing delegate.</summary>
+        /// <param name="field">A tuple of a delegate and its invocation list already in array form.</param>
+        /// <param name="value">The delegate to add.</param>
+        /// <remarks>
+        /// This routine enables code to store a tuple of a delegate and its invocation list.  Adding
+        /// behaves exactly like combining with the delegate, but the invocation list is also updated.
+        /// Thread safety is maintained just as with the code generated by the C# compiler when adding
+        /// to an event.  Storing such a tuple is helpful when the registered delegates are changed
+        /// relatively rarely while invocation via the invocation list happens much more frequently,
+        /// avoiding the need to call GetInvocationList every time invocation needs to happen, as the
+        /// array has already been precomputed.
+        /// </remarks>
+        public static void AddHandler<T>(ref Tuple<T, Delegate[]> field, T value) where T : Delegate
+        {
+            while (true)
+            {
+                Tuple<T, Delegate[]> oldTuple = field;
+                T combinedDelegate = (T)Delegate.Combine(oldTuple?.Item1, value);
+                Tuple<T, Delegate[]> newTuple = combinedDelegate != null ? Tuple.Create(combinedDelegate, combinedDelegate.GetInvocationList()) : null;
+                if (Interlocked.CompareExchange(ref field, newTuple, oldTuple) == oldTuple)
+                {
+                    break;
+                }
+            }
+        }
+
+        /// <summary>Removes a delegate from an existing delegate.</summary>
+        /// <param name="field">A tuple of a delegate and its invocation list already in array form.</param>
+        /// <param name="value">The delegate to remove.</param>
+        public static void RemoveHandler<T>(ref Tuple<T, Delegate[]> field, T value) where T : Delegate
+        {
+            while (true)
+            {
+                Tuple<T, Delegate[]> oldTuple = field;
+                T delegateWithRemoval = (T)Delegate.Remove(oldTuple?.Item1, value);
+                Tuple<T, Delegate[]> newTuple = delegateWithRemoval != null ? Tuple.Create(delegateWithRemoval, delegateWithRemoval.GetInvocationList()) : null;
+                if (Interlocked.CompareExchange(ref field, newTuple, oldTuple) == oldTuple)
+                {
+                    break;
+                }
+            }
+        }
+    }
+}

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/InputManager.cs

@@ -179,49 +179,26 @@ private InputManager()
 
         public event PreProcessInputEventHandler PreProcessInput
         {
-            add
-            {
-                _preProcessInput += value;
-            }
-            remove
-            {
-                _preProcessInput -= value;
-            }
+            add => EventHelper.AddHandler(ref _preProcessInput, value);
+            remove => EventHelper.RemoveHandler(ref _preProcessInput, value);
         }
 
         public event NotifyInputEventHandler PreNotifyInput
         {
-            add
-            {
-                _preNotifyInput += value;
-            }
-            remove
-            {
-                _preNotifyInput -= value;
-            }
-}
+            add => EventHelper.AddHandler(ref _preNotifyInput, value);
+            remove => EventHelper.RemoveHandler(ref _preNotifyInput, value);
+        }
+
         public event NotifyInputEventHandler PostNotifyInput
         {
-            add
-            {
-                _postNotifyInput += value;
-            }
-            remove
-            {
-                _postNotifyInput -= value;
-}
+            add => EventHelper.AddHandler(ref _postNotifyInput, value);
+            remove => EventHelper.RemoveHandler(ref _postNotifyInput, value);
         }
 
         public event ProcessInputEventHandler PostProcessInput
         {
-            add
-            {
-                _postProcessInput += value;
-            }
-            remove
-            {
-                _postProcessInput -= value;
-            }
+            add => EventHelper.AddHandler(ref _postProcessInput, value);
+            remove => EventHelper.RemoveHandler(ref _postProcessInput, value);
         }
 
         /// <summary>
@@ -749,7 +726,7 @@ private bool ProcessStagingArea()
 
                     // Invoke the handlers in reverse order so that handlers that
                     // users add are invoked before handlers in the system.
-                    Delegate[] handlers = _preProcessInput.GetInvocationList();
+                    Delegate[] handlers = _preProcessInput.Item2;
                     for(int i = (handlers.Length - 1); i >= 0; i--)
                     {
                         PreProcessInputEventHandler handler = (PreProcessInputEventHandler) handlers[i];
@@ -772,7 +749,7 @@ private bool ProcessStagingArea()
 
                         // Invoke the handlers in reverse order so that handlers that
                         // users add are invoked before handlers in the system.
-                        Delegate[] handlers = _preNotifyInput.GetInvocationList();
+                        Delegate[] handlers = _preNotifyInput.Item2;
                         for(int i = (handlers.Length - 1); i >= 0; i--)
                         {
                             NotifyInputEventHandler handler = (NotifyInputEventHandler) handlers[i];
@@ -878,7 +855,7 @@ private bool ProcessStagingArea()
 
                         // Invoke the handlers in reverse order so that handlers that
                         // users add are invoked before handlers in the system.
-                        Delegate[] handlers = _postNotifyInput.GetInvocationList();
+                        Delegate[] handlers = _postNotifyInput.Item2;
                         for(int i = (handlers.Length - 1); i >= 0; i--)
                         {
                             NotifyInputEventHandler handler = (NotifyInputEventHandler) handlers[i];
@@ -898,7 +875,7 @@ private bool ProcessStagingArea()
                     {
                         processInputEventArgs.Reset(item, this);
 
-                        RaiseProcessInputEventHandlers(_postProcessInput, processInputEventArgs); 
+                        RaiseProcessInputEventHandlers(_postProcessInput, processInputEventArgs);
 
                         // PreviewInputReport --> InputReport
                         if(item.Input.RoutedEvent == InputManager.PreviewInputReportEvent)
@@ -936,15 +913,15 @@ private bool ProcessStagingArea()
             return handled;
         }
 
-        private void RaiseProcessInputEventHandlers(ProcessInputEventHandler postProcessInput, ProcessInputEventArgs processInputEventArgs)
+        private void RaiseProcessInputEventHandlers(Tuple<ProcessInputEventHandler, Delegate[]> postProcessInput, ProcessInputEventArgs processInputEventArgs)
         {
             processInputEventArgs.StagingItem.Input.MarkAsUserInitiated();
 
             try
             {
                 // Invoke the handlers in reverse order so that handlers that
                 // users add are invoked before handlers in the system.
-                Delegate[] handlers = postProcessInput.GetInvocationList();
+                Delegate[] handlers = postProcessInput.Item2;
                 for(int i = (handlers.Length - 1); i >= 0; i--)
                 {
                     ProcessInputEventHandler handler = (ProcessInputEventHandler) handlers[i];
@@ -974,14 +951,14 @@ private void RequestContinueProcessingStagingArea()
         private ProcessInputEventArgs _processInputEventArgs;
         private PreProcessInputEventArgs _preProcessInputEventArgs;
 
-        //these four events introduced for secutiy purposes
-        private event PreProcessInputEventHandler _preProcessInput;
-
-        private event NotifyInputEventHandler _preNotifyInput;
-
-        private event NotifyInputEventHandler _postNotifyInput;
-
-        private event ProcessInputEventHandler _postProcessInput;
+        // These four events introduced for security purposes. Rather than just store the multicast delegate
+        // and have to do GetInvocationList on each invocation (in order to invoke delegates in reverse-registered
+        // order), we get the invocation list when the events are updated, and then use that cached list
+        // on every invocation.
+        private Tuple<PreProcessInputEventHandler, Delegate[]> _preProcessInput;
+        private Tuple<NotifyInputEventHandler, Delegate[]> _preNotifyInput;
+        private Tuple<NotifyInputEventHandler, Delegate[]> _postNotifyInput;
+        private Tuple<ProcessInputEventHandler, Delegate[]> _postProcessInput;
 
         private event KeyEventHandler _translateAccelerator;
 

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/InterOp/HwndSource.cs

@@ -245,7 +245,7 @@ private void Initialize(HwndSourceParameters parameters)
                 Delegate[] handlers = parameters.HwndSourceHook.GetInvocationList();
                 for (int i = handlers.Length -1; i >= 0; --i)
                 {
-                    _hooks += (HwndSourceHook)handlers[i];
+                    EventHelper.AddHandler(ref _hooks, (HwndSourceHook)handlers[i]);
                 }
                 wrapperHooks[3] = _publicHook;
             }
@@ -376,7 +376,7 @@ public void AddHook(HwndSourceHook hook)
             {
                 _hwndWrapper.AddHook(_publicHook);
             }
-            _hooks += hook;
+            EventHelper.AddHandler(ref _hooks, hook);
         }
 
         /// <summary>
@@ -393,7 +393,7 @@ public void RemoveHook(HwndSourceHook hook)
 
             //this.VerifyAccess();
 
-            _hooks -= hook;
+            EventHelper.RemoveHandler(ref _hooks, hook);
             if(_hooks == null)
             {
                 _hwndWrapper.RemoveHook(_publicHook);
@@ -1635,7 +1635,7 @@ private IntPtr PublicHooksFilterMessage(IntPtr hwnd, int msg, IntPtr wParam, Int
             // would never see the WM_DESTROY etc. message.
             if (_hooks != null)
             {
-                Delegate[] handlers = _hooks.GetInvocationList();
+                Delegate[] handlers = _hooks.Item2;
                 for (int i = handlers.Length -1; i >= 0; --i)
                 {
                     var hook = (HwndSourceHook)handlers[i];
@@ -2820,7 +2820,7 @@ public void Dispose()
 
         private SecurityCriticalDataForSet<Visual>                      _rootVisual;
 
-        private event HwndSourceHook _hooks;
+        private Tuple<HwndSourceHook, Delegate[]> _hooks;
 
         private SecurityCriticalDataClass<HwndMouseInputProvider>      _mouse;