[Squeak-VMdev] Re: Squat VM changes for v4 (was "version 4 changes")

[Andreas R. <and...@gm...>]

Hi Craig,

> > What kind of method-lookup change? What is needed here...
>
> The current Squat implementation checks if the receiver's class is a
> special "proxy" class (currently called "Other"), which is in the
> special objects array. If it is, it kicks the send back to image, using
> the same mechanism as for >>doesNotUnderstand:, so that the message may
> be forwarded by the proxy.

I'm missing something here - if it uses the same mechanism why would we need
to change the lookup? Put differently, wouldn't it have the same effect if
you just make Other a ProtoObject?

Incidentally, talking about message forwarding. We might want to keep in
mind the stuff that Stephen Pair did for the Chango VM - is he on this list?
If not, we should invite him. He had some fairly interesting stuff going
with delegation and that might be of some interest here.

> > I'm slightly hesitent to reserve an object format for something like
> > method dictionary marking. Can you elaborate on why this would be
> > needed?
>
> The VM is the thing that does the activation marking. I'm using that
> mark to tell when any method from a method dictionary has been run; it's
> useful for, e.g., calculating which classes can be swapped out of an
> image at some point in time. (There are also primitives for reading and
> clearing the marks.)

I'm missing something here too (guess I'll have to check the code). This
sounds as if a method dictionary with an extra iVar or so would achieve the
same effect at the same cost.

> > ...we only have so many object format types.
>
> Well, the one I want to use (5) has gone unused for Squeak's entire
> history, as far as I can tell. :)  And it's not the only one (format 7
> is also unused). And in eight years I've yet to hear of anyone else
> wanting one of them. :)  And this is a very good cause. :)  And I'm not
> asking for any additional header bits. ;)  (oops, smilie overload...)

Oh, I'm not saying we shouldn't do this. I'm trying to understand if there
is a "generalized benefit" from it, e.g., what else could one potentially do
with these changes.

> > Hm... something a little more specific would be nice ;-)
>
> 'Sorry, I was pressed for time (still am :). See
> http://www.netjam.org/squat/releases/current/vmChanges.zip . Pick a VM
> and snapshot from http://www.netjam.org/squat/releases/current/#theBits
> to see the image side of things.

Thanks, I'll check it out - guess that'll help with the above.

Cheers,
  - Andreas