Re: Building the igc branch on MS-Windows

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Sat, 27 Apr 2024 09:58:00 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: eller.helmut@gmail.com, emacs-devel@gnu.org
>> 
>>   (gdb) p font
>>   $1 = (struct font *) 0xad2fce0
>>   (gdb) p *$
>>   Cannot access memory at address 0xad2fce0
>
> How do we protect the font objects we create in xfaces.c from being
> GC'ed?  AFAICT, the face's 'font' member is the 'struct font' part of
> a Lisp font object, which comes from Lisp.  But when the Lisp object
> is copied, does MPS update the 'font' pointer of a face?

I'm creating the MPS pools with support for interior pointers, i.e. a
pointer to somehwere inside of an object keeps the object alive. It's
not necessary that there exists a pointer to the object start.

Is that's what happening here?

(Not directly related, just to spread the info: This is necessary anyway
because I'm not using MPS in-band headers. With in-band headers, MPS
would itself do the calculations that I put into client_to_base, and
base_to_client. Base meaning the object start from the perspective of
MPS, and client meaning the object start from Emacs' POV. So, any
reference that Emacs holds is an interior pointer for MPS.

Also handy: a char * into string data keeps the data alive, and makes it
immovable if referenced ambigpusly (control stack). There is no need for
the pinning that is used for the old GC, which prevents string
compaction, or what I called it.)