Merge pull request #10751 from smoogipoo/fix-bdc-threadsafety

osu.Game/Beatmaps/BeatmapDifficultyCache.cs

@@ -30,8 +30,22 @@ namespace osu.Game.Beatmaps
         // Too many simultaneous updates can lead to stutters. One thread seems to work fine for song select display purposes.
         private readonly ThreadedTaskScheduler updateScheduler = new ThreadedTaskScheduler(1, nameof(BeatmapDifficultyCache));
 
-        // All bindables that should be updated along with the current ruleset + mods.
+        /// <summary>
-        private readonly LockedWeakList<BindableStarDifficulty> trackedBindables = new LockedWeakList<BindableStarDifficulty>();
+        /// All bindables that should be updated along with the current ruleset + mods.
+        /// </summary>
+        private readonly WeakList<BindableStarDifficulty> trackedBindables = new WeakList<BindableStarDifficulty>();
+
+        /// <summary>
+        /// Cancellation sources used by tracked bindables.
+        /// </summary>
+        private readonly List<CancellationTokenSource> linkedCancellationSources = new List<CancellationTokenSource>();
+
+        /// <summary>
+        /// Lock to be held when operating on <see cref="trackedBindables"/> or <see cref="linkedCancellationSources"/>.
+        /// </summary>
+        private readonly object bindableUpdateLock = new object();
+
+        private CancellationTokenSource trackedUpdateCancellationSource;
 
         [Resolved]
         private BeatmapManager beatmapManager { get; set; }
@@ -59,7 +73,10 @@ namespace osu.Game.Beatmaps
         public IBindable<StarDifficulty> GetBindableDifficulty([NotNull] BeatmapInfo beatmapInfo, CancellationToken cancellationToken = default)
         {
             var bindable = createBindable(beatmapInfo, currentRuleset.Value, currentMods.Value, cancellationToken);
-            trackedBindables.Add(bindable);
+
+            lock (bindableUpdateLock)
+                trackedBindables.Add(bindable);
+
             return bindable;
         }
 
@@ -86,7 +103,8 @@ namespace osu.Game.Beatmaps
         /// <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;
@@ -140,23 +158,23 @@ namespace osu.Game.Beatmaps
             return DifficultyRating.Easy;
         }
 
-        private CancellationTokenSource trackedUpdateCancellationSource;
-        private readonly List<CancellationTokenSource> linkedCancellationSources = new List<CancellationTokenSource>();
-
         /// <summary>
         /// Updates all tracked <see cref="BindableStarDifficulty"/> using the current ruleset and mods.
         /// </summary>
         private void updateTrackedBindables()
         {
-            cancelTrackedBindableUpdate();
+            lock (bindableUpdateLock)
-            trackedUpdateCancellationSource = new CancellationTokenSource();
-
-            foreach (var b in trackedBindables)
             {
-                var linkedSource = CancellationTokenSource.CreateLinkedTokenSource(trackedUpdateCancellationSource.Token, b.CancellationToken);
+                cancelTrackedBindableUpdate();
-                linkedCancellationSources.Add(linkedSource);
+                trackedUpdateCancellationSource = new CancellationTokenSource();
 
-                updateBindable(b, currentRuleset.Value, currentMods.Value, linkedSource.Token);
+                foreach (var b in trackedBindables)
+                {
+                    var linkedSource = CancellationTokenSource.CreateLinkedTokenSource(trackedUpdateCancellationSource.Token, b.CancellationToken);
+                    linkedCancellationSources.Add(linkedSource);
+
+                    updateBindable(b, currentRuleset.Value, currentMods.Value, linkedSource.Token);
+                }
             }
         }
 
@@ -165,15 +183,18 @@ namespace osu.Game.Beatmaps
         /// </summary>
         private void cancelTrackedBindableUpdate()
         {
-            trackedUpdateCancellationSource?.Cancel();
+            lock (bindableUpdateLock)
-            trackedUpdateCancellationSource = null;
-
-            if (linkedCancellationSources != null)
             {
-                foreach (var c in linkedCancellationSources)
+                trackedUpdateCancellationSource?.Cancel();
-                    c.Dispose();
+                trackedUpdateCancellationSource = null;
 
-                linkedCancellationSources.Clear();
+                if (linkedCancellationSources != null)
+                {
+                    foreach (var c in linkedCancellationSources)
+                        c.Dispose();
+
+                    linkedCancellationSources.Clear();
+                }
             }
         }