From fb2f1224b315a77adce9b2270f33a636601965e9 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 21 Jul 2017 05:58:58 +0900
Subject: [PATCH] Fix carousel filter debounce causing a race condition

Clicking a ruleset button on toolbar would schedule a delayed filter of carousel, which could in turn trigger a beatmap change after pushing a Player. This resolves that by forcing any pending operations to complete.
---
 osu.Game/Screens/Select/BeatmapCarousel.cs |  4 ++++
 osu.Game/Screens/Select/SongSelect.cs      | 13 ++++++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/osu.Game/Screens/Select/BeatmapCarousel.cs b/osu.Game/Screens/Select/BeatmapCarousel.cs
index 0dc5d8074d..96069d8d18 100644
--- a/osu.Game/Screens/Select/BeatmapCarousel.cs
+++ b/osu.Game/Screens/Select/BeatmapCarousel.cs
@@ -232,6 +232,8 @@ namespace osu.Game.Screens.Select
 
         public bool AllowSelection = true;
 
+        public bool PendingFilter => filterTask?.Completed == false;
+
         public void Filter(FilterCriteria newCriteria = null, bool debounce = true)
         {
             if (newCriteria != null)
@@ -263,6 +265,8 @@ namespace osu.Game.Screens.Select
             };
 
             filterTask?.Cancel();
+            filterTask = null;
+
             if (debounce)
                 filterTask = Scheduler.AddDelayed(perform, 250);
             else
diff --git a/osu.Game/Screens/Select/SongSelect.cs b/osu.Game/Screens/Select/SongSelect.cs
index 9e1d230124..59bbb3b3e9 100644
--- a/osu.Game/Screens/Select/SongSelect.cs
+++ b/osu.Game/Screens/Select/SongSelect.cs
@@ -198,13 +198,16 @@ namespace osu.Game.Screens.Select
 
         private void carouselRaisedStart()
         {
-            var pendingSelection = selectionChangedDebounce;
-            selectionChangedDebounce = null;
+            if (carousel.PendingFilter)
+                // if we have a pending filter operation, we want to run it now.
+                // it could change selection (ie. if the ruleset has been changed).
+                carousel.Filter(null, false);
 
-            if (pendingSelection?.Completed == false)
+            if (selectionChangedDebounce?.Completed == false)
             {
-                pendingSelection.RunTask();
-                pendingSelection.Cancel(); // cancel the already scheduled task.
+                selectionChangedDebounce.RunTask();
+                selectionChangedDebounce.Cancel(); // cancel the already scheduled task.
+                selectionChangedDebounce = null;
             }
 
             OnSelected();