PVE Game Freeze Which May Caused By AI Attacking Stealth Units Or Structures

[HansNilhall]

Issue Summary

When AI tries to detect or attack some stealth units or structures, the game then might freeze and can only be closed by task manager. I have received several these kinds of reports from Chinese community and then try to test them out. Now as I myself have reproduced one of that circumstances which might cause bug, I believe it should be an issue.

In RA mod, there are two reports.

1. At the moment when the reporter's Missile Sub was attacked by some AI infantries while the sub was trying submerging after firing missiles, the game froze.
2. In Allies Mission 08b, after laying some mines by using Minelayers on the field, the game might freeze. (This is the circumstances I reproduced)

In SP mod, there are also two reports.

1. The game froze when AI tried to attack the Nod stealth tank which is trying to stealth again after hit-and-run or the buildings which are protected by Nod stealth generator.
2. When AI tried to attack CABAL's deployed Abductor or mines layed by CABAL's Artisan.

The second circumstance is the only one I can reproduce by myself because the others are reported by different Chinese players and I only experience others in multiplayer PVE while we were testing those two problems from SP. And we are using different OS.

System Information

I will use some special marks to show or explain clearly in the section of System Information
bolded texts - means my situation while reproducing the bug;
italic text - means other testers and me while experience the bug in SP;
'...' - means the reporter's OS of the first circumstance of RA.

• Operating System: Win10, 'Win7 64x', Win10 Win7
• .NET / Mono Version: .NET 4.8, 'Unknown', .NET 4.8 .NET 4.7
• OpenRA Version: playtest-20190825, 'release-20190314, SP release-20190623
• Mod: Red Alert, 'Red Alert', Shattered Paradise

Additional Information:

- Steps to reproduce
1. Allies Mission 08b
2. Clear the road to the base
3. Use the minelayers to set mines on the way which enemies must come from
4. Wait or play normally until the game freeze
PS: FiveAces had reported the same thing on discord channel on 26th, Aug 2019.

- Logs
There is no useful log

- OpenRA Replays
Allies 08b - playtest-20190825.zip

- Screenshots & Videos

The sceenshot below was given by the reporters who reports the submarine freeze.
The cursor shows the game was freeze at that moment and in the red circle, an AI rifle man was trying to attack player's missile sub.

The screenshot below was the moment when the game freeze while playing Allies Mission 08b.
The white fog-like thing is the special effect of the app having no respond in Win10.
This one was captured by myself.

[pchote]

Reproduced the freeze in allies-08b and used the debugger to break out and see that this is caused by the lua script calling Actor.QueueActivity which then gets in an endless loop of queuing CallLuaFunc and ReturnToBase within the same tick (with the list continuing to grow without bound when resuming / rebreaking)

[pchote]

Possibly related to:

IMO this is getting pretty hacky. The real issue is that ReturnToBase cancels the whole queue, which is against our own guidelines for how activities should behave.

The proper solution is to remove the activity cancelling from ReturnToBase entirely and let FlyAttack be solely responsible for breaking out of a potential infinite loop. This can be done by checking whether the branch of FlyAttack.Tick that calls ReturnToBase is entered two ticks in a row and going to NextActivity if that is the case.

Originally posted by @tovl in #17030 (comment)

[tovl]

The relevant part of the Lua script:

OpenRA/mods/ra/maps/allies-08b/allies08b-AI.lua

Lines 131 to 150 in acea193

	TargetAndAttack = function(mig, target)
	if not target or target.IsDead or (not target.IsInWorld) then
	local enemies = Utils.Where(greece.GetActors(), function(actor)
	return actor.HasProperty("Health") and actor.Type ~= "brik"
	end)
	if #enemies > 0 then
	target = Utils.Random(enemies)
	end
	end
	if target and mig.AmmoCount() > 0 and mig.CanTarget(target) then
	mig.Attack(target)
	else
	mig.ReturnToBase()
	end
	mig.CallFunc(function()
	TargetAndAttack(mig, target)
	end)
	end

[pchote]

That will certainly do it...

There is a good chance that the issue with submarines / SP units has already been fixed by the activity rework, so the best approach here will be to fix the script issue then consider this solved.

[abcdefg30]

Yes, I couldn't reproduce a freeze in any AI games outside of the missions. So I consider this fixed with #17205 unless we get another reproduction case.