Re: Dumper problems and a possible solutions

[Rich Felker <dalias@libc.org>]

On Wed, Jun 25, 2014 at 10:03:36PM +0400, Dmitry Antipov wrote:
> On 06/24/2014 09:19 PM, Rich Felker wrote:
> 
> >To solve ALL of the problems with the dumper (which seems to be a
> >recurring theme), I have a proposed design to make it fully portable
> >-- even moreso than xemacs "portable dumper" which is still an ugly
> >hack. The idea is simple: after loading all of the lisp objects that
> >need dumping, walk the lisp heap and output a representation for each
> >object as a giant static array in C source format, then compile and
> >link this new translation unit with the rest of the emacs .o files to
> >produce a final emacs binary.
> 
> What about non-Lisp objects?
> 
> It's not too hard to walk through live (reachable) Lisp objects - this
> is exactly what GC mark phase does. It's not too hard to walk through
> all allocated Lisp objects - this is exactly what GC sweep phase does.
> But what about lower-level stuff allocated with malloc at invisible
> from Lisp? Of course, you can do your own serialization for these objects
> as well - but only if you know about their internal structure. What about
> stuff allocated by some external library? In general, you can't parse heap
> (i.e. looking at object, you can't say where the next object is, what is the
> type of next object, etc.). IIUC, "totally portable" heap dumper is impossible
> without having a description of each possible heap object and ability to
> distinguish between different types of objects.

Are there such objects that need to be preserved across dumping? This
is a real question. I'm not familiar enough with emacs' internals to
know whether there are or not, but my impression is that emacs does
not need a fully general process-freeze-and-thaw dumper (in fact it
doesn't even try to be one), and my hope is that only the lisp state,
and perhaps some reasonably-trivial amount of non-lisp data with known
structure, actually needs to be preserved.

Can you or anyone else provide some answers to this question?

Rich