0002499: (master) LUS: WaitForTurn in a loop without sleeps causes stack overflow

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Date Submitted

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0002499

Spring engine

Lua

public

2011-06-27 08:18

2011-07-08 17:22

Reporter

KingRaptor

Assigned To

zerver

Priority

normal

Severity

major

Reproducibility

always

Status

resolved

Resolution

fixed

Product Version

0.82.7+git

Target Version

Fixed in Version

0.82.7+git

Summary

0002499: (master) LUS: WaitForTurn in a loop without sleeps causes stack overflow

Description

Spawning a chickenflyerqueen in ZK and giving it a move order results in:

[f=0000663] [string "LuaGadgets/Gadgets/unit_script.lua"]:312: stack overflow
[f=0000663] stack traceback:
    [string "LuaGadgets/Gadgets/unit_script.lua"]:312: in function 'WaitForTurn'
    [string "scripts/chickenflyerqueen.lua"]:63: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    ...
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function 'Fly'
    [string "scripts/chickenflyerqueen.lua"]:72: in function <[string "scripts/chickenflyerqueen.lua"]:55>

Adding Sleep(0) before or after each WaitForTurn cures the problem.
Adding Sleep(0) at the start of the loop results in a broken animation, but no stack overflow.

Additional Information

Tested with engine version 0.82.3-2330-gab1fc5d

https://code.google.com/p/zero-k/source/browse/trunk/mods/zk/scripts/chickenflyerqueen.lua

A possibly related problem occurs in 0.82.7.1 where using WaitForTurn without any sleeps causes the animation to rapidly speed up until stack overflow. To see this, comment the sleeps out from the Dig() function of https://code.google.com/p/zero-k/source/browse/trunk/mods/zk/scripts/chickenwurm.lua

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Notes
~0006821 jK (developer) 2011-06-28 01:42	local function Fly() if (isMoving) then ... Fly() end end This might not be tail call recursion optimized. Please write KISS code, a loop is a loop and not recursion ...

~0006822 KingRaptor (reporter) 2011-06-28 05:36 Last edited: 2011-06-28 05:42	Using a real loop (while true do) instead of recursion merely causes it to hang instead of stack overflow. Also fixed by Sleep(0). (In fact, the loop "while true do Sleep(0) end" works fine, which comes across as rather illogical.)

~0006823 Kloot (developer) 2011-06-28 12:02	"Using a real loop (while true do) instead of recursion merely causes it to hang instead of stack overflow." Erhm, duh? Lua threads are not system threads! There is always only one executing code at any point in time and it MUST yield to others or return by itself ==> an infinite loop without any Sleep or WaitFor* call WILL monopolize the CPU. We cannot fix stack overflows in bad recursive Lua code either.

~0006824 Kloot (developer) 2011-06-28 12:08	Also, Sleep(0) by design is equal to Sleep(1), Sleep(2), ..., and Sleep(33), the argument is assumed to be in MILLIseconds (because there are 33ms per frame).

~0006832 jK (developer) 2011-06-30 15:25	WaitFor... still had a bug which got fixed in afc991eac3

~0006961 zerver (reporter) 2011-07-08 03:05	FYI, the good old CUnitScript::Tick crashbug came back after this commit, imma fix it

~0006973 zerver (reporter) 2011-07-08 17:22	https://github.com/spring/spring/commit/0d59eb60854e843d24404ed33789ab25a61eb368

Notes

Date Modified	Username	Field	Change
Issue History
2011-06-27 08:18	KingRaptor	New Issue
2011-06-27 08:18	KingRaptor	Graphics Card	=> unknown
2011-06-28 01:42	jK	Note Added: 0006821
2011-06-28 01:46	jK	Status	new => resolved
2011-06-28 01:46	jK	Resolution	open => no change required
2011-06-28 01:46	jK	Assigned To	=> jK
2011-06-28 05:36	KingRaptor	Note Added: 0006822
2011-06-28 05:36	KingRaptor	Status	resolved => assigned
2011-06-28 05:36	KingRaptor	Resolution	no change required => reopened
2011-06-28 05:42	KingRaptor	Note Edited: 0006822
2011-06-28 12:02	Kloot	Note Added: 0006823
2011-06-28 12:08	Kloot	Note Added: 0006824
2011-06-28 12:08	Kloot	Status	assigned => closed
2011-06-28 12:08	Kloot	Resolution	reopened => won't fix
2011-06-30 15:24	jK	Status	closed => assigned
2011-06-30 15:24	jK	Resolution	won't fix => reopened
2011-06-30 15:25	jK	Note Added: 0006832
2011-06-30 15:25	jK	Status	assigned => resolved
2011-06-30 15:25	jK	Resolution	reopened => fixed
2011-07-08 03:05	zerver	Assigned To	jK => zerver
2011-07-08 03:05	zerver	Note Added: 0006961
2011-07-08 03:05	zerver	Status	resolved => feedback
2011-07-08 03:05	zerver	Resolution	fixed => reopened
2011-07-08 17:22	zerver	Note Added: 0006973
2011-07-08 17:22	zerver	Status	feedback => resolved
2011-07-08 17:22	zerver	Fixed in Version	=> 0.82.7+git
2011-07-08 17:22	zerver	Resolution	reopened => fixed

Issue History