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

[Christian Tellefsen <christian.tellefsen@...>]

Jim Whitehead II wrote:
> On Tue, Nov 3, 2009 at 3:53 PM, Peter Cawley <lua@corsix.org> wrote:
>   
> > 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
> > >       
> > 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.
> >     
Thanks, this worked great!

void CoroutineTimeoutHook(lua_State * L, lua_Debug * ar)
{
 luaL_error(L, "Script took too long to execute.");
}

int CoroutineCreate(lua_State * L)
{
 lua_State * L1 = lua_newthread(L);  // L: f, thread
 lua_pushvalue(L, 1);                // L: f, thread, f
 lua_xmove(L, L1, 1);                // L: f, thread    L1: f
 lua_sethook(L1, &CoroutineTimeoutHook, LUA_MASKCOUNT, 10000);

 return 1;
}
> Keep in mind that for certain C functions (like string.find) won't
> call your debug hook in them, so a user script can still tie up the
> system in what appears to be an infinite loop, but really is just code
> that takes a long time to run (all without your hook being called).
>
> - Jim
>
>   
OK, thanks, I'll keep that in mind, or maybe I'll just remove access to 
that function.

Cheers,
Christian.