Fix: Large folders with many PDFs load slowly

src/Files.App/Helpers/Layout/LayoutPreferencesManager.cs

@@ -624,6 +624,8 @@ public static void SetLayoutPreferencesForPath(string? path, LayoutPreferencesIt
 			if (string.IsNullOrEmpty(path))
 				return new();
 
+#if WINDOWS
+			// LINUX-TODO(listing): Uno's grouped CollectionView renders no rows, so Downloads is not grouped by default on Linux
 			if (path == Constants.UserEnvironmentPaths.DownloadsPath)
 			{
 				// Default for downloads folder is to group by date created
@@ -634,7 +636,9 @@ public static void SetLayoutPreferencesForPath(string? path, LayoutPreferencesIt
 					DirectoryGroupByDateUnit = GroupByDateUnit.Year
 				};
 			}
-			else if (LibraryManager.IsLibraryPath(path))
+			else
+#endif
+			if (LibraryManager.IsLibraryPath(path))
 			{
 				// Default for libraries is to group by folder path
 				return new()

src/Files.App/Platforms/Desktop/Services/LinuxIconHelper.cs

@@ -29,7 +29,7 @@ internal static class LinuxIconHelper
 		private static IMimeTypeService Mime => Ioc.Default.GetRequiredService<IMimeTypeService>();
 		private static IUserDirectories Directories => Ioc.Default.GetRequiredService<IUserDirectories>();
 
-		public static async Task<byte[]?> GetIconAsync(string? path, uint size, bool isFolder, IconOptions options)
+		public static async Task<byte[]?> GetIconAsync(string? path, uint size, bool isFolder, IconOptions options, CancellationToken cancellationToken = default)
 		{
 			try
 			{
@@ -42,10 +42,9 @@ internal static class LinuxIconHelper
 
 				if (!string.IsNullOrEmpty(path) && !isFolder && !options.HasFlag(IconOptions.ReturnIconOnly))
 				{
-					var thumbnail = await Thumbnails.GetThumbnailAsync(
-						path,
-						size,
-						options.HasFlag(IconOptions.ReturnOnlyIfCached) ? ThumbnailOptions.ReturnOnlyIfCached : ThumbnailOptions.None);
+					// The cache lookup reads files synchronously, and callers may be on the UI thread
+					var thumbnailOptions = options.HasFlag(IconOptions.ReturnOnlyIfCached) ? ThumbnailOptions.ReturnOnlyIfCached : ThumbnailOptions.None;
+					var thumbnail = await Task.Run(() => Thumbnails.GetThumbnailAsync(path, size, thumbnailOptions, cancellationToken), cancellationToken);
 
 					if (thumbnail is not null)
 						return thumbnail;

src/Files.App/Utils/Storage/Helpers/FileThumbnailHelper.cs

@@ -15,7 +15,7 @@ public static class FileThumbnailHelper
 		/// <summary>
 		/// Returns icon or thumbnail for given file or folder
 		/// </summary>
-		public static async Task<byte[]?> GetIconAsync(string? path, uint requestedSize, bool isFolder, IconOptions iconOptions)
+		public static async Task<byte[]?> GetIconAsync(string? path, uint requestedSize, bool isFolder, IconOptions iconOptions, CancellationToken cancellationToken = default)
 		{
 			var scaledSize = requestedSize * App.AppModel.AppWindowDPI;
 
@@ -26,7 +26,7 @@ public static class FileThumbnailHelper
 				: _standardSizes.FirstOrDefault(s => s >= scaledSize, _standardSizes[^1]);
 
 #if !WINDOWS
-			return await LinuxIconHelper.GetIconAsync(path, size, isFolder, iconOptions);
+			return await LinuxIconHelper.GetIconAsync(path, size, isFolder, iconOptions, cancellationToken);
 #else
 			if (!isFolder && !iconOptions.HasFlag(IconOptions.ReturnIconOnly) && !iconOptions.HasFlag(IconOptions.ReturnOnlyIfCached))
 			{

src/Files.App/ViewModels/ShellViewModel.cs

@@ -1415,7 +1415,8 @@ private async Task LoadThumbnailAsync(ListedItem item, CancellationToken cancell
 							item.ItemPath,
 							thumbnailSize,
 							item.IsFolder,
-							IconOptions.ReturnThumbnailOnly | IconOptions.ReturnOnlyIfCached);
+							IconOptions.ReturnThumbnailOnly | IconOptions.ReturnOnlyIfCached,
+							cancellationToken);
 
 					cancellationToken.ThrowIfCancellationRequested();
 					loadNonCachedThumbnail = true;
@@ -1433,7 +1434,8 @@ private async Task LoadThumbnailAsync(ListedItem item, CancellationToken cancell
 							item.ItemPath,
 							thumbnailSize,
 							item.IsFolder,
-							IconOptions.ReturnIconOnly);
+							IconOptions.ReturnIconOnly,
+							cancellationToken);
 
 					cancellationToken.ThrowIfCancellationRequested();
 				}
@@ -1457,7 +1459,8 @@ await dispatcherQueue.EnqueueOrInvokeAsync(async () =>
 						item.ItemPath,
 						thumbnailSize,
 						item.IsFolder,
-						(returnIconOnly ? IconOptions.ReturnIconOnly : IconOptions.None));
+						(returnIconOnly ? IconOptions.ReturnIconOnly : IconOptions.None),
+						cancellationToken);
 
 				cancellationToken.ThrowIfCancellationRequested();
 			}
@@ -2228,7 +2231,7 @@ private async Task RapidAddItemsToCollectionAsync(string? path, LibraryItem? lib
 
 		public void CloseWatcher()
 		{
-			App.Logger.LogInformation($"CloseWatcher: aProcessQueueAction={aProcessQueueAction?.Status.ToString()}, gitProcessQueueAction={gitProcessQueueAction?.Status.ToString()}");
+			App.Logger.LogDebug($"CloseWatcher: aProcessQueueAction={aProcessQueueAction?.Status.ToString()}, gitProcessQueueAction={gitProcessQueueAction?.Status.ToString()}");
 
 			watcher?.Dispose();
 			watcher = null;

src/Files.App/Views/Layouts/BaseLayoutPage.cs

@@ -1354,7 +1354,7 @@ private void LoadVisibleItemsAfterScrollSettled()
 			}
 
 			if (itemsToLoad.Count is not 0)
-				_ = Parallel.ForEachAsync(itemsToLoad, (item, _) => new ValueTask(LoadItemExtendedPropertiesAsync(item, shellViewModel)));
+				_ = Parallel.ForEachAsync(itemsToLoad, new ParallelOptions { MaxDegreeOfParallelism = 4 }, (item, _) => new ValueTask(LoadItemExtendedPropertiesAsync(item, shellViewModel)));
 		}
 
 		private static async Task LoadItemExtendedPropertiesAsync(ListedItem item, ShellViewModel shellViewModel)