perf(android): Don't refresh memory statistics too often

Author: jeromelaban

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

@@ -1,4 +1,6 @@
-using System;
+#nullable enable
+
+using System;
 using Android.OS;
 using Android.App;
 using Uno.UI;
@@ -7,25 +9,52 @@ namespace Windows.System
 {
 	public partial class MemoryManager
 	{
+		private static ulong _appMemoryUsage;
+		private static ulong _appMemoryUsageLimit;
+
+		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 readonly static long _updateResolution = global::System.Diagnostics.Stopwatch.Frequency;
+
 		public static ulong AppMemoryUsage
 		{
 			get
 			{
-				Debug.MemoryInfo mi = new Debug.MemoryInfo();
-				Debug.GetMemoryInfo(mi);
-				var totalMemory = mi.TotalPss * 1024;
-				return (ulong)totalMemory;
+				Update();
+
+				return _appMemoryUsage;
 			}
 		}
 
 		public static ulong AppMemoryUsageLimit
 		{
 			get
 			{
-				ActivityManager.MemoryInfo memoryInfo = new ActivityManager.MemoryInfo();
-				ActivityManager.FromContext(ContextHelper.Current)?.GetMemoryInfo(memoryInfo);
+				Update();
+
+				return _appMemoryUsageLimit;
+			}
+		}
+
+		private static void Update()
+		{
+			var now = _updateWatch.ElapsedTicks;
+			if (now - _lastUpdate > _updateResolution)
+			{
+				_lastUpdate = now;
+
+				_mi ??= new Debug.MemoryInfo();
+				Debug.GetMemoryInfo(_mi);
+				var totalMemory = _mi.TotalPss * 1024;
+				_appMemoryUsage = (ulong)totalMemory;
+
+				_memoryInfo ??= new ActivityManager.MemoryInfo();
+				ActivityManager.FromContext(ContextHelper.Current)?.GetMemoryInfo(_memoryInfo);
 
-				return AppMemoryUsage + (ulong)memoryInfo.AvailMem - (ulong)memoryInfo.Threshold;
+				_appMemoryUsageLimit = _appMemoryUsage + (ulong)_memoryInfo.AvailMem - (ulong)_memoryInfo.Threshold;
 			}
 		}
 	}