Re: [Caml-list] Documentation request: allocation of bigarrays in C

[Dmitry Bely <dbely@mail.ru>]

Li-Thiao-Té Sébastien <sayan@crans.org> writes:

>>>If you want to be GC-friendly, use the bigarray
>>>allocation macros with a NULL pointer to allocate memory then get a
>>>pointer to the data array.
>> If you need GC-controlled bigarray, why simply not to use
>> Bigarray.Genarray.create?
>>
> Why is there a C bigarray allocation function at all then ? :)

alloc_bigarray_xxx()? Their primary purpose is to allocate a proxy
structure for an external C-allocated data (that cannot be finalized).
data==NULL behaviour IMHO is not for the final user but only for
Bigarray.Genarray.create internal use.

> In my case, I want to read a relatively big file (50MB) containing
> arrays of floats . I use C functions for the raw speed then pass the
> bigarrays to OCaml to do some reordering of the data, and higher-level
> processing.

You should use Bigarray.Genarray.create then pass the created bigarray to C
side using Data_bigarray_val(). Note that the bigarray is allocated with
malloc() outside the Ocaml heap.

> I do not open the file in Ocaml then send a string to C for parsing,
> but rather open the file in C and return the bigarray list to
> Ocaml. (cf my previous mistake on creating Ocaml lists in C on this
> mailing-list)
>
> I have hundreds of such files that I may want to load and compare
> interactively, so reclaiming unused memory is a big bonus.

Sure - Ocaml-allocated bigarrays will be finalized as usual.

- Dmitry Bely