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Re: when GC is permitted

This page is part of the web mail archives of SRFI 50 from before July 7th, 2015. The new archives for SRFI 50 contain all messages, not just those from before July 7th, 2015.

Tom Lord <lord@xxxxxxx> writes:

>    This hypothesis, that you're making a mistake, is reinforced by an
>    experiment that jivera (Matthew Dempsky) carried out.  He thought:
>    "Suppose I have a Scheme implementation that uses a
>    Sperber/Kelsey-style FFI.  And further suppose that I now want that
>    implementation to have a Pika-style FFI.  How hard is that?"  About
>    2-3 pages of trivial code later, and disregarding for the moment
>    the issues we haven't taken up yet about error handling and
>    non-local exits, he had 95% of an implementation.  The only
>    sticking point was on the exact syntax of GCPROtect-family macros:
>    it would take some tweaks to reconcile those in Pika with those in
>    the draft.  We would need to make a trivial addition to the Pika
>    macros to complete the job.

For those interested: http://www.flame.org/~jivera/pika/srfi-50.h

Regarding the current SCM_PROTECT_FRAME macro, even gcc without any
compiler optimization flags is able to use constant folding to reduce
the switch case to just a single function call for common cases of
having a fixed number of local variables.

(I haven't actually worked with S48 or SCSH's FFI so I don't know that
it works -- I wrote it entirely based on what I could understand from
the draft SRFI.)