Cache skin filename to path mapping to reduce realm lookups during gameplay skin changes

osu.Game/Skinning/LegacyDatabasedSkinResourceStore.cs

@@ -3,10 +3,8 @@
 
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using osu.Framework.Extensions;
 using osu.Framework.IO.Stores;
-using osu.Game.Database;
 using osu.Game.Extensions;
 using Realms;
 
@@ -14,12 +12,36 @@ namespace osu.Game.Skinning
 {
     public class LegacyDatabasedSkinResourceStore : ResourceStore<byte[]>
     {
-        private readonly ILive<SkinInfo> source;
+        private readonly Dictionary<string, string> fileToStoragePathMapping = new Dictionary<string, string>();
+
+        private readonly IDisposable subscription;
 
         public LegacyDatabasedSkinResourceStore(SkinInfo source, IResourceStore<byte[]> underlyingStore)
             : base(underlyingStore)
         {
-            this.source = source.ToLive();
+            subscription = source.Files.SubscribeForNotifications((sender, changes, error) =>
+            {
+                if (changes == null)
+                    return;
+
+                // If a large number of changes are made on skin files, this may be better suited to being cleared here
+                // and reinitialised on next usage.
+                initialiseFileCache(source);
+            });
+
+            initialiseFileCache(source);
+        }
+
+        ~LegacyDatabasedSkinResourceStore()
+        {
+            Dispose(false);
+        }
+
+        private void initialiseFileCache(SkinInfo source)
+        {
+            fileToStoragePathMapping.Clear();
+            foreach (var f in source.Files)
+                fileToStoragePathMapping[f.Filename.ToLowerInvariant()] = f.File.GetStoragePath();
         }
 
         protected override IEnumerable<string> GetFilenames(string name)
@@ -32,18 +54,16 @@ protected override IEnumerable<string> GetFilenames(string name)
             }
         }
 
+        protected override void Dispose(bool disposing)
+        {
+            base.Dispose(disposing);
+
+            subscription?.Dispose();
+        }
+
         private string getPathForFile(string filename) =>
-            source.PerformRead(s =>
-            {
-                if (s.IsManaged)
-                {
-                    // avoid enumerating all files if this is a managed realm instance.
-                    return s.Files.Filter(@"Filename ==[c] $0", filename).FirstOrDefault()?.File.GetStoragePath();
-                }
+            fileToStoragePathMapping.TryGetValue(filename.ToLower(), out string path) ? path : null;
 
-                return s.Files.FirstOrDefault(f => string.Equals(f.Filename, filename, StringComparison.OrdinalIgnoreCase))?.File.GetStoragePath();
-            });
-
-        public override IEnumerable<string> GetAvailableResources() => source.PerformRead(s => s.Files.Select(f => f.Filename));
+        public override IEnumerable<string> GetAvailableResources() => fileToStoragePathMapping.Keys;
     }
 }