perf: Reuse java strings instances in TextBlock

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
 			{