[Squeak-e] Programming the VM

[cg at cdegroot.com]

Andreas Raab <squeak-e at lists.squeakfoundation.org> said:
>I don't know where you heard that the object format is going to be changed
>in 3.5 but adding a pointer to every object is unlikely to be done unless
>you have a Very Good Reason(tm). It will instantly break all plugins and the
>added space and GC overhead is not to be taken lightly.
>
Last thing I heard was that there were some changes necessary for
various things, and that 3.5 would be the version where this would, as
far as possible, would all be collected so that we'd have a break in
image file format only once. But that was last October, before I went
into a long dive involving directory services and other ugly business
matters :-)

I've already been thinking about the implications GC-wise and space
wise. Probably some compression is possible and necessary. 90% of all
objects, certainly in the beginning, will point to a default
environment. A bit indicating whether there's additional environment
info could save a lot of space and time. A second bit might indicate
whether a short or long environment pointer is used (6-8 bit index in a
table vs. 32 bit pointer). Immutables probably wouldn't need to have it
at all. 

Anyway, the discussion *might* be premature; however, before diving into
options it would be nice to know how feasible they are. So I fear that
we need to discuss ways *how* to make this happen more-or-less in parallel
with the discussion *what* exactly we want to make happen (e.g., what do
we want to point to). 

In other words, even though it's premature from a technical viewpoint,
as none of use here wants to fork Squeak (I hope) it is probably prudent
to inventory the options for doing things like this as early as possible
and see how/whether support can be raised. Politics, again...



-- 
Cees de Groot               http://www.cdegroot.com     <cg at cdegroot.com>
GnuPG 1024D/E0989E8B 0016 F679 F38D 5946 4ECD  1986 F303 937F E098 9E8B
Cogito ergo evigilo