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Re: GC and simple smobs??

From: David Kastrup
Subject: Re: GC and simple smobs??
Date: Sat, 18 Jun 2022 00:11:30 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux)

Jean Abou Samra <> writes:

> Le 17/06/2022 à 23:46, David Kastrup a écrit :
>> Nope.  They are on the stack.  They may either be immediate SCM values
>> with nothing on the heap (like SCM_EOL or small integers), or they may
>> point to a heap cell.  In that case, scanning the stack during GC will
>> pick up the SCM values and mark the associated cells in the heap.
> Well, OK, they are small stack values each storing a pointer to
> a heap object. Right?

Yup.  Not a pointer in the C meaning but a pointer in the SCM-encoded

>> Why?  There is no allocation happening anywhere, so there is no
>> reason to do garbage collection.  At least I think that is the
>> rationale also covering a lot of Guile-internal code.
> If I understand you correctly, this code doesn't need it, but it would
> if there were a call to scm_something () between LY_ASSERT_SMOBbing
> and the call to Duration::compare?

Yes.  In this case it might make more sense not to store pointers but
actual durations, like

Duration d1 = *LY_ASSERT_SMOB (...);

> I thought you said it was unclear whether BDWGC could run outside of
> Guile allocations, but if it doesn't, I am happy.

I have no idea.  It is somewhat troubling that Guile2 is a lot more
prone to trigger GC problems than Guile1.

David Kastrup

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