Gameplay deadlocks at map start after retry

Describe the bug: Was playing maps, decided to retry the map and ended up stuck at the start without any indication of it trying to start. Pause menu didn’t function, etc. however alt+f4 brought me back to the start with an unhandled exception in the code block below

2020-12-09 21:05:14 [verbose]: working beatmap updated to UNDEAD CORPORATION - Frozen (Daycore) [Everything Will Freeze]
2020-12-09 21:05:19 [verbose]: Screen changed → PlayerLoader
2020-12-09 21:05:24 [verbose]: Screen changed → Player
2020-12-09 21:05:41 [verbose]: Screen changed ← PlayerLoader
2020-12-09 21:05:41 [verbose]: Screen changed → Player
2020-12-09 21:05:41 [verbose]: Unhandled exception has been allowed with 0 more allowable exceptions .
2020-12-09 21:05:41 [error]: An unhandled error has occurred.
2020-12-09 21:05:41 [error]: System.InvalidOperationException: A screen should not be loaded before being pushed.
2020-12-09 21:05:41 [error]: at osu.Framework.Screens.ScreenStack.Push(IScreen source, IScreen newScreen)
2020-12-09 21:05:41 [error]: at osu.Framework.Screens.ScreenExtensions.Push(IScreen screen, IScreen newScreen)
2020-12-09 21:05:41 [error]: at osu.Game.Screens.Play.PlayerLoader.<pushWhenLoaded>b__61_1() in /repos/osu/osu.Game/Screens/Play/PlayerLoader.cs:line 369
2020-12-09 21:05:41 [error]: at osu.Framework.Threading.ScheduledDelegate.RunTaskInternal()
2020-12-09 21:05:41 [error]: at osu.Framework.Threading.Scheduler.Update()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Drawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
2020-12-09 21:05:41 [error]: at osu.Framework.Platform.GameHost.UpdateFrame()
2020-12-09 21:05:41 [error]: at osu.Framework.Threading.GameThread.ProcessFrame()

Screenshots or videos showing encountered issue: https://streamable.com/dgnds9 https://streamable.com/r2i34c

osu!lazer version: Local release build @ 231c3414d7c7fc623f41810b4269fe3f6dea06d0

Logs:

database.log network.log performance.log runtime.log

[Joehuu]

I can reproduce 100% of the time (if you are patient enough of getting second step right):

• load same map ^, or any epilepsy map
• when map is done loading, hover visual settings until it goes to gameplay
• when in player, press quick retry

[peppy]

@bdach seems your suspicion is almost on the mark (although figuring out what was actually going on was made a bit more difficult due to https://github.com/ppy/osu-framework/pull/4084 - meaning the logs show that Player is pushed a final time, but this never actually occurs).

We don’t want to schedule an extra pushWhenLoaded when the operation succeeds. Currently due to it being in finally, it is doing this, running one extra time, which can result in two scenarios:

• The second run happens on returning to the screen, at which point it’s fine (will early return at readyForPush because the player instance is in a Loaded state, not Ready).
• The second run happens on the next frame, before the current player has been displayed. One would think “but this is fine - there’s a null check on scheduledPushPlayer!”, but unfortunately if the OnSuspending is run after the first schedule but before the second, it will trigger a cancelLoad which resets this to null. This allows a second scheduledPushPlayer to occur, to be eventually run after returning to the screen.

A simple solution would be adding a call to cancelLoad() in OnResuming, but not 100% sure we want this level of flaky logic in the first place. Will look at refactoring the whole process, I think.