Re: Guile, C, and Garbage Collection

[Mikael Djurfeldt <mdj@nada.kth.se>]

Jim Blandy <jimb@red-bean.com> writes:

> I really think there ought to be graceful solutions to both of these
> situations.  Given the nature of garbage collection, Guile gives you a
> powerful hooks into that.

I don't know if this qualifies as graceful, but there is a simple
minded alternative to the suggestion I gave in the previous letter if
you want the C objects to point directly to other C objects, but still
want to be able to use the garbage collector to keep track of
references:

Include a "handle" pointing back to the Scheme level object in every C
struct.  This way, C level objects can refer to each other directly by
C pointers, but the garbage collector can still find the corresponding
Scheme level wrapper objects (the smobs):

struct foo {
  SCM handle;
  ...
  struct bar *bar;
  ...
};

struct bar {
  SCM handle;
  ...
};

The markfoo function then contains:

  scm_gc_mark (((struct foo *) SCM_CDR (obj))->bar->handle);

   (or

  return ((struct foo *) SCM_CDR (obj))->bar->handle;)

/mdj