RE: Lua gc in games

["Josh Jensen" <joshj@...>]

Except in Amped's case, running a garbage collection costs 60+
milliseconds.  That's EVERY garbage collection.  There isn't THAT much
data to warrant that kind of time, but it does make sense when each data
hit will likely be a memory cache miss, due to locality.

const data would be an interesting solution to the problem.  I wonder
what it would take to implement it...

Thanks,
Joshua Jensen
Amped: Freestyle Snowboarding
http://www.xbox.com/Games/sports/amped.htm

> -----Original Message-----
> From: Jonathan Branam [mailto:sspeare@sspeare.com] 
> Sent: Sunday, August 05, 2001 4:13 PM
> To: Multiple recipients of list
> Subject: Re: Lua gc in games
> 
> 
> > Re: the Amped gc issue... what happens if you force a gc 
> every frame?
> 
> This can help some problems. As you state, it definitely 
> reduces the unpredictability of the system.
> 
> The main problem with this ends up being the "Lua heap size" 
> (Not sure if there is another term for that...). Lua has to 
> search its entire heap to determine if the one or two (or 
> 300) values you have created this frame are referenced by 
> anything. Or indeed, if one of your 1000 values has now 
> become un-referenced.
> 
> I've been pondering this for a while, and one solution that 
> would probably not be too hard, is to introduce the concept 
> of "const data" to the Lua GC. All of this (somehow specially 
> marked) const data would be placed in a separate set of 
> structures in Lua. When GC fired, it would simply not check 
> this set at all. Also, if a non-const piece of data were to 
> reference this set, the GC would not need to continue 
> collecting in the const data.
> 
> With my limited knowledge of Lua, this seems easier to me 
> than writing a full incremental GC.
> 
> -Jonathan
> 
> ----- Original Message -----
> From: "Thatcher Ulrich" <tu@tulrich.com>
> To: "Multiple recipients of list" <lua-l@tecgraf.puc-rio.br>
> Sent: Sunday, August 05, 2001 2:53 PM
> Subject: Lua gc in games
> 
> 
> >
> > Re: the Amped gc issue... what happens if you force a gc 
> every frame? 
> > That should collect all garbage generated during that frame.  It's 
> > probably high total overhead, compared to doing gc periodically 
> > because I'm guessing the collector visits all objects on 
> the Lua heap 
> > during gc, just to collect a frame's worth of garbage, but then it 
> > should probably keep the worst-case gc time within reason.  
> That is, 
> > if your Lua heap size is within reason...
> >
> > -Thatcher
> >
> >
> 
>