feat(ShadowContainer): cache cleanup based on shadows stats (#853)

(cherry picked from commit b7a3364)

src/Uno.Toolkit.Skia.WinUI/Controls/Shadows/ShadowsCache.cs

@@ -1,5 +1,9 @@
 using System;
 using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Linq;
+using System.Threading.Tasks;
+
 using Microsoft.Extensions.Logging;
 using SkiaSharp;
 using Uno.Extensions;
@@ -8,9 +12,19 @@
 namespace Uno.Toolkit.UI;
 public class ShadowsCache
 {
+	private const int CleanupInterval = 30;
+
 	private static readonly ILogger _logger = typeof(ShadowsCache).Log();
 
-	private readonly ConcurrentDictionary<string, CacheBucket> _shadowsCache = new ConcurrentDictionary<string, CacheBucket>();
+	private static readonly Func<CacheBucket, DateTime, bool> OneHitSinceAShortTime =
+		(bucket, time) => bucket.Hit == 1 && (time - bucket.LastHit).TotalMinutes > 1;
+
+	private static readonly Func<CacheBucket, DateTime, bool> SeveralHitsSinceALongTime =
+		(bucket, time) => bucket.Hit > 1 && (time - bucket.LastHit).TotalMinutes > 3;
+
+	private readonly ConcurrentDictionary<string, CacheBucket> _shadowsCache = new();
+
+	private DateTime _lastCleanupUtcTime = DateTime.UtcNow;
 
 	public void AddOrUpdate(string key, SKImage image)
 	{
@@ -19,17 +33,17 @@ public void AddOrUpdate(string key, SKImage image)
 			_logger.Trace($"[ShadowsCache] AddOrUpdate => key: {key}");
 		}
 
-		var bucket = _shadowsCache.AddOrUpdate(
+		_shadowsCache.AddOrUpdate(
 			key,
-			(key) =>
+			_ =>
 			{
 				if (_logger.IsEnabled(LogLevel.Trace))
 				{
 					_logger.Trace($"[ShadowsCache] inserting new shadow in cache");
 				}
 				return new CacheBucket(image);
 			},
-			(key, existing) =>
+			(_, existing) =>
 			{
 				existing.AddHit();
 				if (_logger.IsEnabled(LogLevel.Trace))
@@ -38,6 +52,8 @@ public void AddOrUpdate(string key, SKImage image)
 				}
 				return existing;
 			});
+
+		CleanupIfNeeded();
 	}
 
 	public bool TryGetValue(string key, out SKImage? image)
@@ -46,6 +62,7 @@ public bool TryGetValue(string key, out SKImage? image)
 		{
 			_logger.Trace($"[ShadowsCache] TryGet => key: {key}");
 		}
+
 		if (_shadowsCache.TryGetValue(key, out var bucket))
 		{
 			bucket.AddHit();
@@ -101,4 +118,57 @@ public void AddHit()
 			LastHit = DateTime.UtcNow;
 		}
 	}
+
+	public async void CleanupIfNeeded()
+	{
+		if (!_shadowsCache.IsEmpty && (DateTime.UtcNow - _lastCleanupUtcTime).TotalSeconds > CleanupInterval)
+		{
+			try
+			{
+				await CleanupAsync().ConfigureAwait(false);
+			}
+			catch (Exception ex)
+			{
+				_logger.Warn($"[ShadowsCache] Cleanup failed: {ex}");
+			}
+		}
+	}
+
+	/// <summary>
+	/// Removing old shadows based on their stats.
+	/// </summary>
+	private Task CleanupAsync()
+	{
+		_lastCleanupUtcTime = DateTime.UtcNow;
+
+		return Task.Run(() =>
+		{
+			var stopwatch = new Stopwatch();
+			if (_logger.IsEnabled(LogLevel.Trace))
+			{
+				stopwatch.Start();
+				_logger.Trace($"[ShadowsCache] Cleanup starting");
+			}
+
+			DateTime utcNow = DateTime.UtcNow;
+			int removedShadows = 0;
+			foreach (var expiredBucket in _shadowsCache
+				.Where(x => OneHitSinceAShortTime(x.Value, utcNow) || SeveralHitsSinceALongTime(x.Value, utcNow)))
+			{
+				if (_shadowsCache.TryRemove(expiredBucket.Key, out _))
+				{
+					removedShadows++;
+				}
+			}
+
+			if (_logger.IsEnabled(LogLevel.Trace))
+			{
+				stopwatch.Stop();
+				if (_logger.IsEnabled(LogLevel.Trace))
+				{
+					_logger.Trace($"[ShadowsCache] Cleanup done in {stopwatch.ElapsedMilliseconds} ms ({removedShadows} shadows removed)");
+				}
+			}
+		});		
+	}
 }