Improve safety of ongoing operation tracker

Finishing an operation started via
`OngoingOperationTracker.BeginOperation()` was risky in cases where the
operation ended at a callback on another thread (which, in the case of
multiplayer, is *most* cases). In particular, if any consumer registered
a callback that mutates transforms when the operation ends, it would
result in crashes after the framework-side safety checks.

Rework `OngoingOperationTracker` into an always-present component
residing in the drawable hierarchy, and ensure that the
`operationInProgress` bindable is always updated on the update thread.
This way consumers don't have to add local schedules in multiple places.

osu.Game.Tests/Visual/Multiplayer/TestSceneCreateMultiplayerMatchButton.cs

@@ -3,18 +3,13 @@
 
 using System;
 using NUnit.Framework;
-using osu.Framework.Allocation;
 using osu.Framework.Graphics;
-using osu.Game.Screens.OnlinePlay;
 using osu.Game.Screens.OnlinePlay.Multiplayer;
 
 namespace osu.Game.Tests.Visual.Multiplayer
 {
     public class TestSceneCreateMultiplayerMatchButton : MultiplayerTestScene
     {
-        [Cached]
-        private OngoingOperationTracker ongoingOperationTracker = new OngoingOperationTracker();
-
         private CreateMultiplayerMatchButton button;
 
         public override void SetUpSteps()
@@ -36,7 +31,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
 
             assertButtonEnableState(true);
 
-            AddStep("begin joining room", () => joiningRoomOperation = ongoingOperationTracker.BeginOperation());
+            AddStep("begin joining room", () => joiningRoomOperation = OngoingOperationTracker.BeginOperation());
             assertButtonEnableState(false);
 
             AddStep("end joining room", () => joiningRoomOperation.Dispose());

osu.Game/Screens/OnlinePlay/OngoingOperationTracker.cs

@@ -4,6 +4,7 @@
 using System;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Graphics;
 
 namespace osu.Game.Screens.OnlinePlay
 {
@@ -11,7 +12,7 @@ namespace osu.Game.Screens.OnlinePlay
     /// Utility class to track ongoing online operations' progress.
     /// Can be used to disable interactivity while waiting for a response from online sources.
     /// </summary>
-    public class OngoingOperationTracker
+    public class OngoingOperationTracker : Component
     {
         /// <summary>
         /// Whether there is an online operation in progress.
@@ -22,6 +23,11 @@ namespace osu.Game.Screens.OnlinePlay
 
         private LeasedBindable<bool> leasedInProgress;
 
+        public OngoingOperationTracker()
+        {
+            AlwaysPresent = true;
+        }
+
         /// <summary>
         /// Begins tracking a new online operation.
         /// </summary>
@@ -37,7 +43,8 @@ namespace osu.Game.Screens.OnlinePlay
             leasedInProgress = inProgress.BeginLease(true);
             leasedInProgress.Value = true;
 
-            return new InvokeOnDisposal(endOperation);
+            // for extra safety, marshal the end of operation back to the update thread if necessary.
+            return new InvokeOnDisposal(() => Scheduler.Add(endOperation, false));
         }
 
         private void endOperation()

osu.Game/Screens/OnlinePlay/OnlinePlayScreen.cs

@@ -54,7 +54,7 @@ namespace osu.Game.Screens.OnlinePlay
         private readonly Bindable<FilterCriteria> currentFilter = new Bindable<FilterCriteria>(new FilterCriteria());
 
         [Cached]
-        private readonly OngoingOperationTracker ongoingOperationTracker = new OngoingOperationTracker();
+        private OngoingOperationTracker ongoingOperationTracker { get; set; }
 
         [Resolved(CanBeNull = true)]
         private MusicController music { get; set; }
@@ -144,7 +144,8 @@ namespace osu.Game.Screens.OnlinePlay
                         };
                         button.Action = () => OpenNewRoom();
                     }),
-                    RoomManager = CreateRoomManager()
+                    RoomManager = CreateRoomManager(),
+                    ongoingOperationTracker = new OngoingOperationTracker()
                 }
             };
 

osu.Game/Tests/Visual/Multiplayer/MultiplayerTestScene.cs

@@ -24,7 +24,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
         public Bindable<FilterCriteria> Filter { get; }
 
         [Cached]
-        public OngoingOperationTracker OngoingOperationTracker { get; } = new OngoingOperationTracker();
+        public OngoingOperationTracker OngoingOperationTracker { get; }
 
         protected override Container<Drawable> Content => content;
         private readonly TestMultiplayerRoomContainer content;
@@ -39,6 +39,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
             Client = content.Client;
             RoomManager = content.RoomManager;
             Filter = content.Filter;
+            OngoingOperationTracker = content.OngoingOperationTracker;
         }
 
         [SetUp]

osu.Game/Tests/Visual/Multiplayer/TestMultiplayerRoomContainer.cs

@@ -25,6 +25,9 @@ namespace osu.Game.Tests.Visual.Multiplayer
         [Cached]
         public readonly Bindable<FilterCriteria> Filter = new Bindable<FilterCriteria>(new FilterCriteria());
 
+        [Cached]
+        public readonly OngoingOperationTracker OngoingOperationTracker;
+
         public TestMultiplayerRoomContainer()
         {
             RelativeSizeAxes = Axes.Both;
@@ -33,6 +36,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
             {
                 Client = new TestMultiplayerClient(),
                 RoomManager = new TestMultiplayerRoomManager(),
+                OngoingOperationTracker = new OngoingOperationTracker(),
                 content = new Container { RelativeSizeAxes = Axes.Both }
             });
         }