Re: scratch/igc fe90d556834: Make glyphs ambiguous roots

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

Helmut Eller <eller.helmut@gmail.com> writes:

> On Sun, Jul 28 2024, Gerd Moellmann wrote:
>
>>     We cannot trace glyphs in fix_window because we don't have exclusive
>>     access to glyph_rows and glyphs. (An optimal solution would allocate
>>     glyphs from MPS, and change data structures in a way that everything
>>     needed (row->used, row->enabled_p) is available for the scanner.)
>
> I don't understand this.  Glyph_rows aren't allocated in MPS-managed
> memory so there are no memory barriers to worry about.

True.

> While fix_frame runs, all other threads are suspended.

I don't think that is guranteed. but please check.

Frames are not roots, so fix_frame can only assume exclusive access to
the frame struct itself. Other threads can work on glyph_rows, glyphs
and so on while fix_frame runs.

> So why don't we have exclusive access? And why is it not a problem for
> FRAME_FONT, FRAME_DISPLAY_INFO, etc?

FRAME_X_DISPLAY_INFO has the same problem. It's just that I had the
glyphs on my todo list. With frame->font I don't see a problem. Fonts
are pvecs so we only have to fix the pointer to it, and fix_font should
do the rest.

BTW, unrelated. Do you observe problems in clear_face_cache? I'm getting
EXC_BAD_ACCESS from accessing face->font->driver, sometimes, as if the
face hadn't been scanned. But the face looks okay, as far as the
face_cache is concerned. Happens since I change the default font to
JetBrains Mono. (And happened before that change above.)