Improve performance of watcher

Files/Files.csproj

@@ -275,6 +275,7 @@
     <Compile Include="Helpers\SidebarHelpers.cs" />
     <Compile Include="Helpers\XamlHelpers\DependencyObjectHelpers.cs" />
     <Compile Include="Helpers\XamlHelpers\SystemTypeToXaml.cs" />
+    <Compile Include="Helpers\AsyncManualResetEvent.cs" />
     <Compile Include="IBaseLayout.cs" />
     <Compile Include="Interacts\BaseLayoutCommandImplementationModel.cs" />
     <Compile Include="Interacts\BaseLayoutCommandsViewModel.cs" />

Files/Filesystem/ListedItem.cs

@@ -13,6 +13,7 @@
 using System.Collections.ObjectModel;
 using System.IO;
 using System.Linq;
+using System.Threading;
 using Windows.Storage;
 using Windows.UI.Xaml.Media.Imaging;
 
@@ -22,7 +23,16 @@ public class ListedItem : ObservableObject, IGroupableItem
     {
         public bool IsHiddenItem { get; set; } = false;
         public StorageItemTypes PrimaryItemAttribute { get; set; }
-        public bool ItemPropertiesInitialized { get; set; } = false;
+
+        private volatile int itemPropertiesInitialized = 0;
+        public bool ItemPropertiesInitialized
+        {
+            get => itemPropertiesInitialized == 1;
+            set
+            {
+                Interlocked.Exchange(ref itemPropertiesInitialized, value ? 1 : 0);
+            }
+        }
 
         public string ItemTooltipText
         {

Files/Helpers/AsyncManualResetEvent.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Files.Helpers
+{
+    public class AsyncManualResetEvent
+    {
+        private volatile TaskCompletionSource<bool> m_tcs = new TaskCompletionSource<bool>();
+
+        public async Task WaitAsync(CancellationToken cancellationToken = default)
+        {
+            var tcs = m_tcs;
+            var cancelTcs = new TaskCompletionSource<bool>();
+
+            cancellationToken.Register(
+                s => ((TaskCompletionSource<bool>)s).TrySetCanceled(), cancelTcs);
+
+            await await Task.WhenAny(tcs.Task, cancelTcs.Task);
+        }
+
+        private async Task<bool> Delay(int milliseconds)
+        {
+            await Task.Delay(milliseconds);
+            return false;
+        }
+
+        public async Task<bool> WaitAsync(int milliseconds, CancellationToken cancellationToken = default)
+        {
+            var tcs = m_tcs;
+            var cancelTcs = new TaskCompletionSource<bool>();
+
+            cancellationToken.Register(
+                s => ((TaskCompletionSource<bool>)s).TrySetCanceled(), cancelTcs);
+
+            return await await Task.WhenAny(tcs.Task, cancelTcs.Task, Delay(milliseconds));
+        }
+
+        public void Set()
+        {
+            var tcs = m_tcs;
+            Task.Factory.StartNew(s => ((TaskCompletionSource<bool>)s).TrySetResult(true),
+                tcs, CancellationToken.None, TaskCreationOptions.PreferFairness, TaskScheduler.Default);
+            tcs.Task.Wait();
+        }
+
+        public void Reset()
+        {
+            while (true)
+            {
+                var tcs = m_tcs;
+                if (!tcs.Task.IsCompleted ||
+                    Interlocked.CompareExchange(ref m_tcs, new TaskCompletionSource<bool>(), tcs) == tcs)
+                    return;
+            }
+        }
+    }
+}