Allow unsubscribing from solo statistics updates

This is more of a safety item. To avoid potential duplicate key in
dictionary errors (and also avoid being slightly memory-leaky), allow
`SoloStatisticsWatcher` consumers to dispose of the subscriptions they
take out.

osu.Game.Tests/Visual/Online/TestSceneSoloStatisticsWatcher.cs

@@ -35,6 +35,8 @@ public partial class TestSceneSoloStatisticsWatcher : OsuTestScene
         private Action<GetUsersRequest>? handleGetUsersRequest;
         private Action<GetUserRequest>? handleGetUserRequest;
 
+        private IDisposable? subscription;
+
         private readonly Dictionary<(int userId, string rulesetName), UserStatistics> serverSideStatistics = new Dictionary<(int userId, string rulesetName), UserStatistics>();
 
         [SetUpSteps]
@@ -246,6 +248,26 @@ public void TestIgnoredScoreUpdateIsMergedIntoNextOne()
             AddAssert("values after are correct", () => update!.After.TotalScore, () => Is.EqualTo(6_000_000));
         }
 
+        [Test]
+        public void TestStatisticsUpdateNotFiredAfterSubscriptionDisposal()
+        {
+            int userId = getUserId();
+            setUpUser(userId);
+
+            long scoreId = getScoreId();
+            var ruleset = new OsuRuleset().RulesetInfo;
+
+            SoloStatisticsUpdate? update = null;
+            registerForUpdates(scoreId, ruleset, receivedUpdate => update = receivedUpdate);
+            AddStep("unsubscribe", () => subscription!.Dispose());
+
+            feignScoreProcessing(userId, ruleset, 5_000_000);
+
+            AddStep("signal score processed", () => ((ISpectatorClient)spectatorClient).UserScoreProcessed(userId, scoreId));
+            AddWaitStep("wait a bit", 5);
+            AddAssert("update not received", () => update == null);
+        }
+
         private int nextUserId = 2000;
         private long nextScoreId = 50000;
 
@@ -266,7 +288,7 @@ private void setUpUser(int userId)
         }
 
         private void registerForUpdates(long scoreId, RulesetInfo rulesetInfo, Action<SoloStatisticsUpdate> onUpdateReady) =>
-            AddStep("register for updates", () => watcher.RegisterForStatisticsUpdateAfter(
+            AddStep("register for updates", () => subscription = watcher.RegisterForStatisticsUpdateAfter(
                 new ScoreInfo(Beatmap.Value.BeatmapInfo, new OsuRuleset().RulesetInfo, new RealmUser())
                 {
                     Ruleset = rulesetInfo,

osu.Game/Online/Solo/SoloStatisticsWatcher.cs

@@ -46,24 +46,30 @@ protected override void LoadComplete()
         /// </summary>
         /// <param name="score">The score to listen for the statistics update for.</param>
         /// <param name="onUpdateReady">The callback to be invoked once the statistics update has been prepared.</param>
-        public void RegisterForStatisticsUpdateAfter(ScoreInfo score, Action<SoloStatisticsUpdate> onUpdateReady) => Schedule(() =>
+        /// <returns>An <see cref="IDisposable"/> representing the subscription. Disposing it is equivalent to unsubscribing from future notifications.</returns>
+        public IDisposable RegisterForStatisticsUpdateAfter(ScoreInfo score, Action<SoloStatisticsUpdate> onUpdateReady)
         {
-            if (!api.IsLoggedIn)
-                return;
+            Schedule(() =>
+            {
+                if (!api.IsLoggedIn)
+                    return;
 
-            if (!score.Ruleset.IsLegacyRuleset() || score.OnlineID <= 0)
-                return;
+                if (!score.Ruleset.IsLegacyRuleset() || score.OnlineID <= 0)
+                    return;
 
-            var callback = new StatisticsUpdateCallback(score, onUpdateReady);
+                var callback = new StatisticsUpdateCallback(score, onUpdateReady);
 
-            if (lastProcessedScoreId == score.OnlineID)
-            {
-                requestStatisticsUpdate(api.LocalUser.Value.Id, callback);
-                return;
-            }
+                if (lastProcessedScoreId == score.OnlineID)
+                {
+                    requestStatisticsUpdate(api.LocalUser.Value.Id, callback);
+                    return;
+                }
 
-            callbacks.Add(score.OnlineID, callback);
-        });
+                callbacks.Add(score.OnlineID, callback);
+            });
+
+            return new InvokeOnDisposal(() => Schedule(() => callbacks.Remove(score.OnlineID)));
+        }
 
         private void onUserChanged(APIUser? localUser) => Schedule(() =>
         {

osu.Game/Screens/Ranking/SoloResultsScreen.cs

@@ -32,6 +32,7 @@ public partial class SoloResultsScreen : ResultsScreen
         [Resolved]
         private SoloStatisticsWatcher soloStatisticsWatcher { get; set; } = null!;
 
+        private IDisposable? statisticsSubscription;
         private readonly Bindable<SoloStatisticsUpdate?> statisticsUpdate = new Bindable<SoloStatisticsUpdate?>();
 
         public SoloResultsScreen(ScoreInfo score, bool allowRetry)
@@ -44,7 +45,7 @@ protected override void LoadComplete()
             base.LoadComplete();
 
             if (ShowUserStatistics)
-                soloStatisticsWatcher.RegisterForStatisticsUpdateAfter(Score, update => statisticsUpdate.Value = update);
+                statisticsSubscription = soloStatisticsWatcher.RegisterForStatisticsUpdateAfter(Score, update => statisticsUpdate.Value = update);
         }
 
         protected override StatisticsPanel CreateStatisticsPanel()
@@ -75,6 +76,7 @@ protected override void Dispose(bool isDisposing)
             base.Dispose(isDisposing);
 
             getScoreRequest?.Cancel();
+            statisticsSubscription?.Dispose();
         }
     }
 }