Fix unsafe list manipulation in BeatmapDifficultyCache

osu.Game/Beatmaps/BeatmapDifficultyCache.cs

@@ -31,7 +31,7 @@ public class BeatmapDifficultyCache : MemoryCachingComponent<BeatmapDifficultyCa
         private readonly ThreadedTaskScheduler updateScheduler = new ThreadedTaskScheduler(1, nameof(BeatmapDifficultyCache));
 
         // All bindables that should be updated along with the current ruleset + mods.
-        private readonly LockedWeakList<BindableStarDifficulty> trackedBindables = new LockedWeakList<BindableStarDifficulty>();
+        private readonly WeakList<BindableStarDifficulty> trackedBindables = new WeakList<BindableStarDifficulty>();
 
         [Resolved]
         private BeatmapManager beatmapManager { get; set; }
@@ -59,7 +59,10 @@ protected override void LoadComplete()
         public IBindable<StarDifficulty> GetBindableDifficulty([NotNull] BeatmapInfo beatmapInfo, CancellationToken cancellationToken = default)
         {
             var bindable = createBindable(beatmapInfo, currentRuleset.Value, currentMods.Value, cancellationToken);
+
+            lock (trackedBindables)
                 trackedBindables.Add(bindable);
+
             return bindable;
         }
 
@@ -86,7 +89,8 @@ public IBindable<StarDifficulty> GetBindableDifficulty([NotNull] BeatmapInfo bea
         /// <param name="mods">The <see cref="Mod"/>s to get the difficulty with.</param>
         /// <param name="cancellationToken">An optional <see cref="CancellationToken"/> which stops computing the star difficulty.</param>
         /// <returns>The <see cref="StarDifficulty"/>.</returns>
-        public Task<StarDifficulty> GetDifficultyAsync([NotNull] BeatmapInfo beatmapInfo, [CanBeNull] RulesetInfo rulesetInfo = null, [CanBeNull] IEnumerable<Mod> mods = null, CancellationToken cancellationToken = default)
+        public Task<StarDifficulty> GetDifficultyAsync([NotNull] BeatmapInfo beatmapInfo, [CanBeNull] RulesetInfo rulesetInfo = null, [CanBeNull] IEnumerable<Mod> mods = null,
+                                                       CancellationToken cancellationToken = default)
         {
             // In the case that the user hasn't given us a ruleset, use the beatmap's default ruleset.
             rulesetInfo ??= beatmapInfo.Ruleset;
@@ -147,6 +151,8 @@ public static DifficultyRating GetDifficultyRating(double starRating)
         /// Updates all tracked <see cref="BindableStarDifficulty"/> using the current ruleset and mods.
         /// </summary>
         private void updateTrackedBindables()
+        {
+            lock (trackedBindables)
             {
                 cancelTrackedBindableUpdate();
                 trackedUpdateCancellationSource = new CancellationTokenSource();
@@ -159,11 +165,14 @@ private void updateTrackedBindables()
                     updateBindable(b, currentRuleset.Value, currentMods.Value, linkedSource.Token);
                 }
             }
+        }
 
         /// <summary>
         /// Cancels the existing update of all tracked <see cref="BindableStarDifficulty"/> via <see cref="updateTrackedBindables"/>.
         /// </summary>
         private void cancelTrackedBindableUpdate()
+        {
+            lock (trackedBindables)
             {
                 trackedUpdateCancellationSource?.Cancel();
                 trackedUpdateCancellationSource = null;
@@ -176,6 +185,7 @@ private void cancelTrackedBindableUpdate()
                     linkedCancellationSources.Clear();
                 }
             }
+        }
 
         /// <summary>
         /// Creates a new <see cref="BindableStarDifficulty"/> and triggers an initial value update.