Re: [RFC] Moving to Guile 2.2 and away from GUB

[David Kastrup]

David Kastrup <dak@gnu.org> writes:

> Jonas Hahnfeld via Discussions on LilyPond development
> <lilypond-devel@gnu.org> writes:
>
>> Am Donnerstag, dem 25.11.2021 um 08:40 +0100 schrieb Jonas Hahnfeld via
>> Discussions on LilyPond development:
>>> Am Mittwoch, dem 24.11.2021 um 23:01 +0100 schrieb Han-Wen Nienhuys:
>>> > On Wed, Nov 24, 2021 at 8:13 PM Jonas Hahnfeld via Discussions on
>>> > LilyPond development <lilypond-devel@gnu.org> wrote:
>>> > > Assuming no major problems are found, we could then move completely to
>>> > > Guile 2.2 and do releases without GUB. Both steps still require a bit
>>> > > of work; I'm relatively sure there is still a GC related issue causing
>>> > > (very rare) crashes with Guile 2.2
>>> > 
>>> > can you say more about this?
>>> 
>>> Not really: I remember weird crashes with dumps that were not
>>> immediately obvious.
>>
>> It's relatively reproducible, I get it every 2nd-3rd time for full
>> 'make doc's. Looking at the core dump, it's crashing in
>> System::derived_mark when marking all_elements_ because the std::vector
>> has garbage in its size field (it was probably freed). What I don't
>> understand is how that can happen since the only way of setting
>> all_elements_ is in System::init_elements where the originating SCM is
>> also protected...
>
> My guess is that std::vector is not freed but rather not initialised.
> That kind of thing is what the Preinit class is supposed to prevent, but
> System does not use it.
>
> Note also that all_elements_ is initialised to nullptr only _after_
> garbage collection has already been activated: the in-class
> initialisation syntax makes it easier to gloss over initialisation order
> (which is not changed).
>
> I'll try GC-proofing System.  Only time will tell whether this makes a
> difference and/or whether other problems remain.

Somewhat embarrassingly, it would not appear that anything protects
*all_elements_ as such (only its elements are protected in
System::derived_mark).  That would be kind of a WTF even with Guile-1.8
.

-- 
David Kastrup