Re: Preventing Lua scripts that never return from freezing the host application

[Peter Cawley <lua@...>]

On Tue, Nov 3, 2009 at 3:46 PM, Christian Tellefsen
<christian.tellefsen@funcom.com> wrote:
> I'm investigating using Lua as a scripting language for content designers.
> If I want to make sure that none of the designer-supplied scripts can loop
> forever and freeze the host application, how would I do that?
>
> Sample problem code:
>
> f = coroutine.create(function() while true do print('x') end end) -- No
> yield()
> coroutine.resume(f) -- Oh no
>
> Some possible solutions I'm looking at:
> - Change the interpreter, so that it returns an error if we've spent too
> much time / done too many operations.
>
> - Run Lua in a separate thread and somehow stop it if it takes too long.
>
> - Wrap f in code that calls yield(), and disallow bytecode in f that
> contains loops or backwards jumps. This would of course greatly limit what
> can be in a script. Something like this:
>
> mycode.create = function(f)
> assert(mycode.checknoloops(f))
> return coroutine.create(function() f() coroutine.yield() end)
> end
>
> - Alternatively, don't fix it in code, just spend some time on teaching the
> content designers to write their scripts right.
>
> If you have any suggestions or experience on how to best attack this
> problem, I'd be grateful.
>
> Cheers,
> Christian.
>

I would use lua_sethook, with LUA_MASKCOUNT and some value between 50
and 500. This will call your hook function at a regular interval, and
then you can abort if things are taking too long. You'll have to do
this for each thread though, so you'll have to export slightly tweaked
versions of the coroutine.xyz functions to your scripts to add
automatic hooking.