I'm not sure, but I think I can be content with passing Racket bytes across the foreign interface boundary for the C runtime to use given the u8vector equivalence. Only thing I'm not clear on: Is it a good idea for me to designate the byte string as a _gcpointer on the "*" marked line, or does it not matter?
(define-ffi-definer define-ff (ffi-lib doesnt-matter)) (define-ff fill_up (_fun _pointer _int -> _void)) ; * (define size 2) (define buffer (make-bytes size)) (fill_up buffer size) On 5/23/21 8:45 PM, Philip McGrath wrote: > On Sun, May 23, 2021 at 7:57 PM Matthew Flatt <mfl...@cs.utah.edu> wrote: > >> At Sun, 23 May 2021 14:57:42 +0000, Sage Gerard wrote: >>> Is there a cross-VM way to pass an arbitrary input port to the C >>> runtime (e.g. via open-input-bytes), such that the C runtime can read >>> bytes on its own? >> >> No, not unless you know that the port's implementation is sufficiently >> constrained. In general, reading from a port can involve thread >> switches and synchronization, and those are not allowed in callbacks >> from foreign libraries. > > Off hand, I think some some version of "sanitizing" an arbitrary port for use > from C is used by: > > - `racket/system` > ([here](https://github.com/racket/racket/blob/448b77a6629c68659e1360fbe9f9e1ecea078f9c/racket/collects/racket/system.rkt#L98-L114) > and > [here](https://github.com/racket/racket/blob/448b77a6629c68659e1360fbe9f9e1ecea078f9c/racket/collects/racket/system.rkt#L173-L193)), > where the implementation comes from `racket/private/streams`; > - `racket/draw`, for the various parts of Cairo that can read from or write > to ports, in `racket/draw/unsafe/callback` (and maybe something similar in > `racket/draw/private/write-bytes`?); and > - `readline`, which uses callbacks rather than creating file-stream ports. > > Would it make sense to expose some part of this functionality as a new > primitive? > > (I'm not familiar with all of the constraints in these use-cases: maybe > they're different enough that the answer is "no".) > > -Philip > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > To view this discussion on the web visit > [https://groups.google.com/d/msgid/racket-users/010001799bd5ab46-d39f83a5-bb2d-49e5-8ce2-3315307742ac-000000%40email.amazonses.com](https://groups.google.com/d/msgid/racket-users/010001799bd5ab46-d39f83a5-bb2d-49e5-8ce2-3315307742ac-000000%40email.amazonses.com?utm_medium=email&utm_source=footer). -- ~slg -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/31b6053a-e1ed-3cd8-2e2b-d9ebb5a086d5%40sagegerard.com.
