Replace ArrayList/ICollection used for changelog in CollectionView wi…

…th generic List (#9853)

* Replace ArrayList/ICollection with List<NotifyCollectionChangedEventArgs>

* Rename EmptyArrayList -> s_emptyList

* Values inside changeLog can never be NULL and we no longer need to cast

* _changeLog can never be NULL, re-init is under same lock

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Data/CollectionView.cs

@@ -1208,7 +1208,7 @@ protected virtual void OnAllowsCrossThreadChangesChanged()
         /// </notes>
         protected void ClearPendingChanges()
         {
-            lock(_changeLog.SyncRoot)
+            lock (_changeLogLock)
             {
                 _changeLog.Clear();
                 _tempChangeLog.Clear();
@@ -1227,7 +1227,7 @@ protected void ClearPendingChanges()
         /// </notes>
         protected void ProcessPendingChanges()
         {
-            lock(_changeLog.SyncRoot)
+            lock (_changeLogLock)
             {
                 ProcessChangeLog(_changeLog, true);
                 _changeLog.Clear();
@@ -1815,24 +1815,17 @@ private void EndDefer()
         ///     processed.
         /// </summary>
         /// <param name="changeLog">
-        ///     ArrayList of NotifyCollectionChangedEventArgs that could not be precessed.
+        ///     List of NotifyCollectionChangedEventArgs that could not be precessed.
         /// </param>
-        private void DeferProcessing(ICollection changeLog)
+        private void DeferProcessing(List<NotifyCollectionChangedEventArgs> changeLog)
         {
             Debug.Assert(changeLog != null && changeLog.Count > 0, "don't defer when there's no work");
 
-            lock(SyncRoot)
+            lock (SyncRoot)
             {
-                lock(_changeLog.SyncRoot)
+                lock (_changeLogLock)
                 {
-                    if (_changeLog == null)
-                    {
-                        _changeLog = new ArrayList(changeLog);
-                    }
-                    else
-                    {
-                        _changeLog.InsertRange(0, changeLog);
-                    }
+                    _changeLog.InsertRange(0, changeLog);
 
                     if (_databindOperation != null)
                     {
@@ -1854,21 +1847,15 @@ private void DeferProcessing(ICollection changeLog)
         /// <param name="changeLog">
         ///     List of NotifyCollectionChangedEventArgs that is to be processed.
         /// </param>
-        private ICollection ProcessChangeLog(ArrayList changeLog, bool processAll=false)
+        private List<NotifyCollectionChangedEventArgs> ProcessChangeLog(List<NotifyCollectionChangedEventArgs> changeLog, bool processAll = false)
         {
             int currentIndex = 0;
             bool mustDeferProcessing = false;
             long beginTime = DateTime.Now.Ticks;
-            int startCount = changeLog.Count;
 
-            for ( ; currentIndex < changeLog.Count && !(mustDeferProcessing); currentIndex++)
+            for ( ; currentIndex < changeLog.Count && !mustDeferProcessing; currentIndex++)
             {
-                NotifyCollectionChangedEventArgs args = changeLog[currentIndex] as NotifyCollectionChangedEventArgs;
-
-                if (args != null)
-                {
-                    ProcessCollectionChanged(args);
-                }
+                ProcessCollectionChanged(changeLog[currentIndex]);
 
                 if (!processAll)
                 {
@@ -1879,7 +1866,7 @@ private ICollection ProcessChangeLog(ArrayList changeLog, bool processAll=false)
             if (mustDeferProcessing && currentIndex < changeLog.Count)
             {
                 // create an unprocessed subset of changeLog
-                changeLog.RemoveRange(0,currentIndex);
+                changeLog.RemoveRange(0, currentIndex);
                 return changeLog;
             }
 
@@ -1907,9 +1894,9 @@ private void SetFlag(CollectionViewFlags flags, bool value)
         // Post a change on the UI thread Dispatcher and updated the _changeLog.
         private void PostChange(NotifyCollectionChangedEventArgs args)
         {
-            lock(SyncRoot)
+            lock (SyncRoot)
             {
-                lock(_changeLog.SyncRoot)
+                lock (_changeLogLock)
                 {
                     // we can ignore everything before a Reset
                     if (args.Action == NotifyCollectionChangedAction.Reset)
@@ -1948,26 +1935,26 @@ private object ProcessInvoke(object arg)
         {
             // work on a private copy of the change log, so that other threads
             // can add to the main change log
-            lock(SyncRoot)
+            lock (SyncRoot)
             {
-                lock(_changeLog.SyncRoot)
+                lock (_changeLogLock)
                 {
                     _databindOperation = null;
                     _tempChangeLog = _changeLog;
-                    _changeLog = new ArrayList();
+                    _changeLog = new List<NotifyCollectionChangedEventArgs>();
                 }
             }
 
             // process the changes
-            ICollection unprocessedChanges = ProcessChangeLog(_tempChangeLog);
+            List<NotifyCollectionChangedEventArgs> unprocessedChanges = ProcessChangeLog(_tempChangeLog);
 
             // if changes remain (because we ran out of time), reschedule them
             if (unprocessedChanges != null && unprocessedChanges.Count > 0)
             {
                 DeferProcessing(unprocessedChanges);
             }
 
-            _tempChangeLog = EmptyArrayList;
+            _tempChangeLog = s_emptyList;
 
             return null;
         }
@@ -2154,8 +2141,11 @@ private enum CollectionViewFlags
         //------------------------------------------------------
         #region Private Fields
 
-        ArrayList               _changeLog = new ArrayList();
-        ArrayList               _tempChangeLog = EmptyArrayList;
+        private readonly Lock _changeLogLock = new();
+
+        private List<NotifyCollectionChangedEventArgs> _changeLog = new();
+        private List<NotifyCollectionChangedEventArgs> _tempChangeLog = s_emptyList;
+
         DataBindOperation       _databindOperation;
         object                  _vmData;            // view manager's private data
         IEnumerable             _sourceCollection;  // the underlying collection
@@ -2173,7 +2163,8 @@ private enum CollectionViewFlags
         object                  _syncObject = new object();
         DataBindEngine          _engine;
         int                     _timestamp;
-        static readonly ArrayList EmptyArrayList = new ArrayList();
+
+        private static readonly List<NotifyCollectionChangedEventArgs> s_emptyList = new();
         static readonly string IEnumerableT = typeof(IEnumerable<>).Name;
         internal static readonly object NoNewItem = new NamedObject("NoNewItem");