Re: Garbage collection

["Thatcher Ulrich" <tu@...>]

On Nov 01, 2002 at 02:10 -0800, James McCartney wrote:
> 
> On Friday, November 1, 2002, at 12:32  PM, Steve Dekorte wrote:
> 
> >On Friday, November 1, 2002, at 12:21 PM, James McCartney wrote:
> >>On Thursday, October 31, 2002, at 03:59  PM, Steve Dekorte wrote:
> >>>so only the freed objects are touched on a sweep.
> >>
> >>Just to press the point, with Baker's treadmill you don't even have 
> >>to do that.
> >
> >I just made a small change to make the definitions of black and white 
> >dynamic that avoids it. Maybe this is equivalent to "Baker's 
> >treadmill"? The descriptions I've read of it weren't very clear to me.
> 
> With the treadmill you've got linked lists of grey, black, white and
> free. To scan an object you remove it from the grey list to black
> and put all of the objects it points to onto the grey list. Once the
> grey list is exhausted then everything on the white list is not live
> and so the entire white list can be linked onto the free list. This
> requires changing 6 list pointers. Then you change the meaning of
> the color bits so that black now means white and start over.

This is cool, but one problem I have with this is that unless you
sweep, the "free" objects don't get returned to the C allocator (you
don't call C's free() on them).  Then, when you go to allocate new
objects, the "free list" is essentially an unsorted bag of
different-sized chunks.  For most Lua purposes, I imagine that an
explicit sweep, to finalize and call free(), would be more desirable.

-- 
Thatcher Ulrich
http://tulrich.com