Questions about the gc

Questions about the gc

[Thiago F.G. Albuquerque]

Hi,

I am new to guile; I am trying to understand how it works. Does it use a 
separate stack, or it uses the C stack? If the latter is the case, how 
does the gc know which elements of the stack are pointers? And, among the 
pointers, how does is know which ones point to guile objects?

TIA,
Thiago

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Re: Questions about the gc

[Stephen Compall]

"Thiago F.G. Albuquerque" <tfga@terra.com.br> writes:

> Does [Guile] use a separate stack, or it uses the C stack?

C stack.

> If the latter is the case, how does the gc know which elements of
> the stack are pointers?

It assumes all elements are pointers.

> And, among the pointers, how does is know which ones point to guile
> objects?

Guile knows the pointer ranges it cares about.  These are organized
into areas of memory called "cards".  If a pointer (anything on the
stack between the bottom and current sp, again) points to a cell
location in one of the cards, and the cell is allocated, the cell gets
marked.  Depending on the type of the cell, you may enter recursive
marking.

OT: Other possibilities for GC include reference counting (a pain, as
in Python) and explicit gcproing (as in Emacs).  Neither of these does
nearly as good a job of separating out the GC code from the "normal"
code; in fact, they don't even try.  With mark/sweep, you only need
occasionally scm_remember_upto_here_* in certain special cases.

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