perf: Reuse android java String instances in TextBlock

src/Uno.Foundation/Metadata/ApiInformation.cs

@@ -29,7 +29,10 @@ internal static void RegisterAssembly(Assembly assembly)
 		{
 			lock (_assemblies)
 			{
-				_assemblies.Add(assembly);
+				if (!_assemblies.Contains(assembly))
+				{
+					_assemblies.Add(assembly);
+				}
 			}
 		}
 

src/Uno.UI.RuntimeTests/Tests/Windows_System/Given_Launcher.cs

@@ -8,6 +8,7 @@
 
 namespace Uno.UI.RuntimeTests.Tests.Windows_System
 {
+
 	[TestClass]
 	public class Given_Launcher
 	{

src/Uno.UI.RuntimeTests/Tests/Windows_System/Given_MemoryManager.cs

@@ -0,0 +1,34 @@
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Windows.System;
+
+namespace Uno.UI.RuntimeTests.Tests.Windows_System
+{
+	[TestClass]
+	public class Given_MemoryManager
+	{
+		[TestMethod]
+		public void When_AppMemoryUsage()
+		{
+			EnsureApiAvailable("AppMemoryUsage");
+
+			Assert.AreNotEqual(0, MemoryManager.AppMemoryUsage);
+		}
+
+		[TestMethod]
+		public void When_AppMemoryUsageLimit()
+		{
+			EnsureApiAvailable("AppMemoryUsageLimit");
+
+			Assert.AreNotEqual(0, MemoryManager.AppMemoryUsageLimit);
+		}
+
+		private void EnsureApiAvailable(string propertyName)
+		{
+			if(!Windows.Foundation.Metadata.ApiInformation.IsPropertyPresent("Windows.System.MemoryManager", propertyName))
+			{
+				Assert.Inconclusive($"The Api {propertyName} is not implemented");
+			}
+		}
+	}
+}

src/Uno.UI/UI/Xaml/Application.cs

@@ -62,6 +62,7 @@ static Application()
 		{
 			ApiInformation.RegisterAssembly(typeof(Application).Assembly);
 			ApiInformation.RegisterAssembly(typeof(Windows.Storage.ApplicationData).Assembly);
+			ApiInformation.RegisterAssembly(typeof(Windows.UI.Composition.Compositor).Assembly);
 
 			Uno.Helpers.DispatcherTimerProxy.SetDispatcherTimerGetter(() => new DispatcherTimer());
 			Uno.Helpers.VisualTreeHelperProxy.SetCloseAllFlyoutsAction(() => Media.VisualTreeHelper.CloseAllFlyouts());

src/Uno.UI/UI/Xaml/Controls/TextBlock/JavaStringCache.android.cs

@@ -0,0 +1,189 @@
+#nullable enable
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading;
+using System.Text;
+using Windows.Foundation;
+
+using Uno;
+using Uno.Extensions;
+using Uno.UI;
+using Uno.Foundation.Logging;
+using Windows.UI.Xaml.Media;
+using Uno.Collections;
+using Android.Security.Keystore;
+using Java.Security;
+using Uno.Buffers;
+using Windows.System;
+
+namespace Windows.UI.Xaml.Controls
+{
+	/// <summary>
+	/// A TextBlock measure cache for non-formatted text.
+	/// </summary>
+	internal static class JavaStringCache
+	{
+		private static Logger _log = typeof(JavaStringCache).Log();
+		private static Stopwatch _watch = Stopwatch.StartNew();
+		private static HashtableEx _table = new();
+		private static TimeSpan _lastScavenge;
+		private static object _gate = new();
+
+		internal static readonly TimeSpan LowMemoryTrimInterval = TimeSpan.FromMinutes(5);
+		internal static readonly TimeSpan MediumMemoryTrimInterval = TimeSpan.FromMinutes(3);
+		internal static readonly TimeSpan HighMemoryTrimInterval = TimeSpan.FromMinutes(1);
+		internal static readonly TimeSpan OverLimitMemoryTrimInterval = TimeSpan.FromMinutes(.5);
+
+		internal static readonly TimeSpan ScavengeInterval = TimeSpan.FromMinutes(.5);
+
+		private static DefaultArrayPoolPlatformProvider _platformProvider = new DefaultArrayPoolPlatformProvider();
+
+		/// <summary>Determines if automatic memory management is enabled</summary>
+		private static readonly bool _automaticManagement;
+		/// <summary>Determines if GC trim callback has been registerd if non-zero</summary>
+		private static int _trimCallbackCreated;
+
+		private record KeyEntry(string Value, Java.Lang.String NativeValue)
+		{
+			public TimeSpan LastUse { get; set; } = _watch.Elapsed;
+		}
+
+		static JavaStringCache()
+		{
+			_automaticManagement = WinRTFeatureConfiguration.ArrayPool.EnableAutomaticMemoryManagement && _platformProvider.CanUseMemoryManager;
+		}
+
+		/// <summary>
+		/// Gets a potentially cached native instance of a .NET string
+		/// </summary>
+		/// <param name="value"></param>
+		/// <returns></returns>
+		public static Java.Lang.String GetNativeString(string value)
+		{
+			TryInitializeMemoryManagement();
+
+			Scavenge();
+
+			lock (_gate)
+			{
+				if (_table.TryGetValue(value, out var result) && result is KeyEntry entry)
+				{
+					if (_log.IsEnabled(LogLevel.Trace))
+					{
+						_log.Trace($"Reusing native string: [{value}]");
+					}
+
+					entry.LastUse = _watch.Elapsed;
+					return entry.NativeValue;
+				}
+				else
+				{
+					if (_log.IsEnabled(LogLevel.Trace))
+					{
+						_log.Trace($"Creating native string for [{value}]");
+					}
+
+					var javaString = new Java.Lang.String(value);
+					_table[value] = new KeyEntry(value, javaString);
+					return javaString;
+				}
+			}
+		}
+
+		private static void TryInitializeMemoryManagement()
+		{
+			if (_automaticManagement && Interlocked.Exchange(ref _trimCallbackCreated, 1) == 0)
+			{
+				if (_log.IsEnabled(LogLevel.Debug))
+				{
+					_log.Debug($"Using automatic memory management");
+				}
+
+				_platformProvider.RegisterTrimCallback(_ => Trim(), _gate);
+			}
+			else
+			{
+				if (_log.IsEnabled(LogLevel.Debug))
+				{
+					_log.Debug($"Using manual memory management");
+				}
+			}
+		}
+
+		private static bool Trim()
+		{
+			if (!_automaticManagement)
+			{
+				return false;
+			}
+
+			var threshold = _platformProvider?.AppMemoryUsageLevel switch
+			{
+				AppMemoryUsageLevel.Low => LowMemoryTrimInterval,
+				AppMemoryUsageLevel.Medium => MediumMemoryTrimInterval,
+				AppMemoryUsageLevel.High => HighMemoryTrimInterval,
+				AppMemoryUsageLevel.OverLimit => OverLimitMemoryTrimInterval,
+				_ => LowMemoryTrimInterval
+			};
+
+			if (_log.IsEnabled(LogLevel.Trace))
+			{
+				_log.Trace($"Memory pressure is {_platformProvider?.AppMemoryUsageLevel}, using trim interval of {threshold}");
+			}
+
+			Trim(threshold);
+
+			return true;
+		}
+
+		private static void Scavenge()
+		{
+			if (!_automaticManagement)
+			{
+				if (_lastScavenge + ScavengeInterval < _watch.Elapsed)
+				{
+					_lastScavenge = _watch.Elapsed;
+					Trim(LowMemoryTrimInterval);
+				}
+			}
+		}
+
+		private static void Trim(TimeSpan interval)
+		{
+			lock (_gate)
+			{
+				List<string>? entries = null;
+				foreach (var entry in _table.Values)
+				{
+					if (entry is KeyEntry keyEntry && keyEntry.LastUse + interval < _watch.Elapsed)
+					{
+						entries ??= new();
+						entries.Add(keyEntry.Value);
+					}
+				}
+
+				if (entries is not null)
+				{
+					if (_log.IsEnabled(LogLevel.Debug))
+					{
+						_log.Debug($"Trimming {entries.Count} native strings unused since {interval}");
+					}
+
+					foreach (var entry in entries)
+					{
+						_table.Remove(entry);
+					}
+				}
+				else
+				{
+					if (_log.IsEnabled(LogLevel.Trace))
+					{
+						_log.Trace($"Nothing to trim for the past {interval}");
+					}
+				}
+			}
+		}
+	}
+}

src/Uno.UI/UI/Xaml/Controls/TextBlock/TextBlock.Android.cs

@@ -263,7 +263,7 @@ private Java.Lang.ICharSequence GetTextFormatted()
 			}
 			else if (UseInlinesFastPath)
 			{
-				return new Java.Lang.String(Text);
+				return JavaStringCache.GetNativeString(Text);
 			}
 			else
 			{

src/Uno.UI/UI/Xaml/NativeApplication.cs

@@ -9,6 +9,7 @@
 using Windows.UI.StartScreen;
 using Android.Content;
 using Uno.Extensions;
+using Windows.Foundation.Metadata;
 
 using System.ComponentModel;
 using Uno.Foundation.Logging;
@@ -31,6 +32,12 @@ public class NativeApplication : Android.App.Application
 		public NativeApplication(AppBuilder appBuilder, IntPtr javaReference, Android.Runtime.JniHandleOwnership transfer)
 			: base(javaReference, transfer)
 		{
+			// Register assemblies earlier than Application itself, otherwise
+			// ApiInformation may return APIs as not implemented incorrectly.
+			ApiInformation.RegisterAssembly(typeof(Application).Assembly);
+			ApiInformation.RegisterAssembly(typeof(Windows.Storage.ApplicationData).Assembly);
+			ApiInformation.RegisterAssembly(typeof(Windows.UI.Composition.Compositor).Assembly);
+
 			// Delay create the Windows.UI.Xaml.Application in order to get the
 			// Android.App.Application.Context to be populated properly. This enables
 			// APIs such as Windows.Storage.ApplicationData.Current.LocalSettings to function properly.

src/Uno.UWP/System/MemoryManager.Android.cs

@@ -15,9 +15,14 @@ public partial class MemoryManager
 		private static Debug.MemoryInfo? _mi;
 		private static ActivityManager.MemoryInfo? _memoryInfo;
 		private static global::System.Diagnostics.Stopwatch _updateWatch = global::System.Diagnostics.Stopwatch.StartNew();
-		private static long _lastUpdate = long.MinValue;
+		private static TimeSpan _lastUpdate = TimeSpan.FromSeconds(-_updateInterval.TotalSeconds);
 
-		private readonly static long _updateResolution = global::System.Diagnostics.Stopwatch.Frequency;
+		private readonly static TimeSpan _updateInterval = TimeSpan.FromSeconds(10);
+
+		static MemoryManager()
+		{
+			IsAvailable = true;
+		}
 
 		public static ulong AppMemoryUsage
 		{
@@ -41,8 +46,8 @@ public static ulong AppMemoryUsageLimit
 
 		private static void Update()
 		{
-			var now = _updateWatch.ElapsedTicks;
-			if (now - _lastUpdate > _updateResolution)
+			var now = _updateWatch.Elapsed;
+			if (_lastUpdate + _updateInterval < now)
 			{
 				_lastUpdate = now;