Re: Buffer-/frame-local variables [Was: Re: Make buffer- and frame-locals a misc object]

[Dmitry Antipov]

On 08/17/2012 05:20 PM, Stefan Monnier wrote:

> Another reason is that until they're initialized, the fields contain
> invalid values, so if the GC sees them we're in trouble, right?

Not quite.  In our terms, the core thing for simple generational GC is:

struct Lisp_Foo
{
  Lisp_Object bar;
  Lisp_Object baz;
};

void
foo_set_bar (Lisp_Object foo, Lisp_Object bar)
{
  if (object_generation (foo) == OLD && object_generation (bar) == NEW)
    /* This function should record all pointer-type Lisp_Objects
       from new generation which are accessible from old generation.
       Such objects will be considered as a part of the root set at
       the next generational collection.  */
    record_intergenerational_object (bar);
  XFOO (foo)->bar = bar;
}

/* Likewise for foo_set_baz.  */

Lisp_Object
make_foo (Lisp_Object bar, Lisp_Object baz)
{
  Lisp_Object foo = allocate_foo ();    /* At this point, object_generation 
(foo) is always NEW.  */
  foo_set_bar (foo, bar);               /* Since foo is NEW, barrier action 
isn't raised whatever bar is;
                                           don't care about old (uninitialized) 
XFOO (foo)->bar here.  */
  foo_set_baz (foo, baz);               /* Likewise.  */
  return foo;
}

> -           valcontents = BLV_VALUE (blv);
> +           valcontents = XCDR (blv->valcell);
>
> Please don't: BLV_VALUE is more clear and abstract (same applies to
> other places where you replace BLV_VALUE with XCDR (blv->valcell)).
>
> -#define BLV_FOUND(blv) \
> +get_blv_found (struct Lisp_Buffer_Local_Value *blv)
>
> Why add a "get_" prefix?
> Elisp and Emacs generally uses "<type>-<field>" for accessors and
> "set-<type>-<field>" for setters.

Fixed and installed as 109660.

Dmitry