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Re: Rational

From: Hans Åberg
Subject: Re: Rational
Date: Tue, 22 May 2018 23:34:23 +0200

> On 22 May 2018, at 23:28, David Kastrup <address@hidden> wrote:
> Hans Åberg <address@hidden> writes:
>>> On 22 May 2018, at 22:53, David Kastrup <address@hidden> wrote:
>>>>> This was somewhat complicated by some Midi classes being heap-allocated
>>>>> and containing Rational/Moment members: those Midi classes would have to
>>>>> become SCM-connected.  I did some work on that, don't remember how
>>>>> complete it was.
>>>> Guile uses the Boehm GC.
>>> Not Guile 1, and LilyPond will have large amounts of heap space outside
>>> of Boehm's fully automated sweep areas even in Guile 2 for efficiency
>>> and compatibility reasons.
>> Something for the future then.
>>>> I wrote a C++ wrap for that latter, too. As it turns out to be
>>>> difficult to keep of pointers into the GC heap, I had to use only
>>>> those that it supplies. Do you do that?
>>> I don't know what "I had to use only those that it supplies" is supposed
>>> to mean, so I cannot answer the question.
>> In addition to the collected GC_malloc, there are
>> GC_malloc_uncollectable and GC_free that correspond to malloc and
>> free. If one uses the latter pair and have pointers into the GC heap,
>> they may suddenly disappear, causing strange memory errors.
> That's why we don't do that.
>> In addition, beware that on some platforms, the GC must be initialized
>> before the first use (like on MacOS), and if one is using global C++
>> objects with heap allocations, that must occur before those being
>> initialized, which is before 'main' starts.
> Uhm, you _are_ aware that LilyPond has been used for large scores with
> Guile data structures for 20+ years?  Don't you think people might have
> noticed a problem in the mean time?  If you want to contribute useful
> advice, it might be a good idea to actually look into the LilyPond code
> base.  The vast majority of LilyPond's memory management in connection
> with Guile is in lily/include/smobs.hh and lily/include/smobs.tcc .

So you don't know anything about the Boehm GC?

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