Simplify flow of cancellation token

osu.Game/Online/Leaderboards/Leaderboard.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using JetBrains.Annotations;
@@ -13,7 +14,6 @@ using osu.Framework.Graphics;
 using osu.Framework.Graphics.Colour;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Sprites;
-using osu.Framework.Threading;
 using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.Cursor;
 using osu.Game.Graphics.UserInterface;
@@ -44,10 +44,9 @@ namespace osu.Game.Online.Leaderboards
 
         private readonly LoadingSpinner loading;
 
-        private CancellationTokenSource showScoresCancellationSource;
+        private CancellationTokenSource currentFetchCancellationSource;
 
-        private APIRequest getScoresRequest;
+        private APIRequest fetchScoresRequest;
-        private ScheduledDelegate getScoresRequestCallback;
 
         [Resolved(CanBeNull = true)]
         private IAPIProvider api { get; set; }
@@ -62,7 +61,6 @@ namespace osu.Game.Online.Leaderboards
             protected set
             {
                 scores = value;
-
                 updateScoresDrawables();
             }
         }
@@ -177,9 +175,10 @@ namespace osu.Game.Online.Leaderboards
         /// <summary>
         /// Performs a fetch/refresh of scores to be displayed.
         /// </summary>
+        /// <param name="cancellationToken"></param>
         /// <returns>An <see cref="APIRequest"/> responsible for the fetch operation. This will be queued and performed automatically.</returns>
         [CanBeNull]
-        protected abstract APIRequest FetchScores();
+        protected abstract APIRequest FetchScores(CancellationToken cancellationToken);
 
         protected abstract LeaderboardScore CreateDrawableScore(TScoreInfo model, int index);
 
@@ -187,37 +186,36 @@ namespace osu.Game.Online.Leaderboards
 
         private void refetchScores()
         {
-            cancelPendingWork();
+            Reset();
 
             PlaceholderState = PlaceholderState.Retrieving;
             loading.Show();
 
-            getScoresRequest = FetchScores();
+            currentFetchCancellationSource = new CancellationTokenSource();
 
-            if (getScoresRequest == null)
+            fetchScoresRequest = FetchScores(currentFetchCancellationSource.Token);
+
+            if (fetchScoresRequest == null)
                 return;
 
-            getScoresRequest.Failure += e => getScoresRequestCallback = Schedule(() =>
+            fetchScoresRequest.Failure += e => Schedule(() =>
             {
-                if (e is OperationCanceledException)
+                if (e is OperationCanceledException || currentFetchCancellationSource.IsCancellationRequested)
                     return;
 
                 PlaceholderState = PlaceholderState.NetworkFailure;
             });
 
-            api?.Queue(getScoresRequest);
+            api?.Queue(fetchScoresRequest);
         }
 
         private void cancelPendingWork()
         {
-            showScoresCancellationSource?.Cancel();
+            currentFetchCancellationSource?.Cancel();
-            showScoresCancellationSource = null;
+            currentFetchCancellationSource = null;
 
-            getScoresRequest?.Cancel();
+            fetchScoresRequest?.Cancel();
-            getScoresRequest = null;
+            fetchScoresRequest = null;
-
-            getScoresRequestCallback?.Cancel();
-            getScoresRequestCallback = null;
         }
 
         #region Placeholder handling
@@ -279,8 +277,6 @@ namespace osu.Game.Online.Leaderboards
             scrollFlow?.FadeOut(fade_duration, Easing.OutQuint).Expire();
             scrollFlow = null;
 
-            showScoresCancellationSource?.Cancel();
-
             if (scores?.Any() != true)
             {
                 loading.Hide();
@@ -288,6 +284,8 @@ namespace osu.Game.Online.Leaderboards
                 return;
             }
 
+            Debug.Assert(!currentFetchCancellationSource.IsCancellationRequested);
+
             // ensure placeholder is hidden when displaying scores
             PlaceholderState = PlaceholderState.Successful;
 
@@ -315,7 +313,7 @@ namespace osu.Game.Online.Leaderboards
 
                 scrollContainer.ScrollToStart(false);
                 loading.Hide();
-            }, (showScoresCancellationSource = new CancellationTokenSource()).Token);
+            }, currentFetchCancellationSource.Token);
         }, false);
 
         private void replacePlaceholder(Placeholder placeholder)

osu.Game/Screens/OnlinePlay/Match/Components/MatchLeaderboard.cs

@@ -1,6 +1,7 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Threading;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Game.Online.API;
@@ -30,7 +31,7 @@ namespace osu.Game.Screens.OnlinePlay.Match.Components
 
         protected override bool IsOnlineScope => true;
 
-        protected override APIRequest FetchScores()
+        protected override APIRequest FetchScores(CancellationToken cancellationToken)
         {
             if (roomId.Value == null)
                 return null;
@@ -39,6 +40,9 @@ namespace osu.Game.Screens.OnlinePlay.Match.Components
 
             req.Success += r =>
             {
+                if (cancellationToken.IsCancellationRequested)
+                    return;
+
                 Scores = r.Leaderboard;
                 TopScore = r.UserScore;
             };

osu.Game/Screens/Select/Leaderboards/BeatmapLeaderboard.cs

@@ -108,13 +108,8 @@ namespace osu.Game.Screens.Select.Leaderboards
 
         protected override bool IsOnlineScope => Scope != BeatmapLeaderboardScope.Local;
 
-        private CancellationTokenSource loadCancellationSource;
+        protected override APIRequest FetchScores(CancellationToken cancellationToken)
-
-        protected override APIRequest FetchScores()
         {
-            loadCancellationSource?.Cancel();
-            loadCancellationSource = new CancellationTokenSource();
-
             var fetchBeatmapInfo = BeatmapInfo;
 
             if (fetchBeatmapInfo == null)
@@ -125,7 +120,7 @@ namespace osu.Game.Screens.Select.Leaderboards
 
             if (Scope == BeatmapLeaderboardScope.Local)
             {
-                subscribeToLocalScores();
+                subscribeToLocalScores(cancellationToken);
 
                 return null;
             }
@@ -160,10 +155,10 @@ namespace osu.Game.Screens.Select.Leaderboards
 
             req.Success += r =>
             {
-                scoreManager.OrderByTotalScoreAsync(r.Scores.Select(s => s.CreateScoreInfo(rulesets, fetchBeatmapInfo)).ToArray(), loadCancellationSource.Token)
+                scoreManager.OrderByTotalScoreAsync(r.Scores.Select(s => s.CreateScoreInfo(rulesets, fetchBeatmapInfo)).ToArray(), cancellationToken)
                             .ContinueWith(task => Schedule(() =>
                             {
-                                if (loadCancellationSource.IsCancellationRequested)
+                                if (cancellationToken.IsCancellationRequested)
                                     return;
 
                                 Scores = task.GetResultSafely();
@@ -184,7 +179,7 @@ namespace osu.Game.Screens.Select.Leaderboards
             Action = () => ScoreSelected?.Invoke(model)
         };
 
-        private void subscribeToLocalScores()
+        private void subscribeToLocalScores(CancellationToken cancellationToken)
         {
             scoreSubscription?.Dispose();
             scoreSubscription = null;
@@ -197,35 +192,35 @@ namespace osu.Game.Screens.Select.Leaderboards
                                           + $" AND {nameof(ScoreInfo.Ruleset)}.{nameof(RulesetInfo.ShortName)} == $1"
                                           + $" AND {nameof(ScoreInfo.DeletePending)} == false"
                     , beatmapInfo.ID, ruleset.Value.ShortName), localScoresChanged);
-        }
 
-        private void localScoresChanged(IRealmCollection<ScoreInfo> sender, ChangeSet changes, Exception exception)
+            void localScoresChanged(IRealmCollection<ScoreInfo> sender, ChangeSet changes, Exception exception)
-        {
-            if (IsOnlineScope)
-                return;
-
-            var scores = sender.AsEnumerable();
-
-            if (filterMods && !mods.Value.Any())
             {
-                // we need to filter out all scores that have any mods to get all local nomod scores
+                if (IsOnlineScope || cancellationToken.IsCancellationRequested)
-                scores = scores.Where(s => !s.Mods.Any());
+                    return;
-            }
-            else if (filterMods)
-            {
-                // otherwise find all the scores that have *any* of the currently selected mods (similar to how web applies mod filters)
-                // we're creating and using a string list representation of selected mods so that it can be translated into the DB query itself
-                var selectedMods = mods.Value.Select(m => m.Acronym);
-                scores = scores.Where(s => s.Mods.Any(m => selectedMods.Contains(m.Acronym)));
-            }
 
-            scores = scores.Detach();
+                var scores = sender.AsEnumerable();
 
-            scoreManager.OrderByTotalScoreAsync(scores.ToArray(), loadCancellationSource.Token)
+                if (filterMods && !mods.Value.Any())
-                        .ContinueWith(ordered =>
+                {
-                        {
+                    // we need to filter out all scores that have any mods to get all local nomod scores
-                            Scores = ordered.GetResultSafely();
+                    scores = scores.Where(s => !s.Mods.Any());
-                        }, TaskContinuationOptions.OnlyOnRanToCompletion);
+                }
+                else if (filterMods)
+                {
+                    // otherwise find all the scores that have *any* of the currently selected mods (similar to how web applies mod filters)
+                    // we're creating and using a string list representation of selected mods so that it can be translated into the DB query itself
+                    var selectedMods = mods.Value.Select(m => m.Acronym);
+                    scores = scores.Where(s => s.Mods.Any(m => selectedMods.Contains(m.Acronym)));
+                }
+
+                scores = scores.Detach();
+
+                scoreManager.OrderByTotalScoreAsync(scores.ToArray(), cancellationToken)
+                            .ContinueWith(ordered =>
+                            {
+                                Scores = ordered.GetResultSafely();
+                            }, TaskContinuationOptions.OnlyOnRanToCompletion);
+            }
         }
 
         protected override void Dispose(bool isDisposing)