Re: [Caml-list] Storing ocaml values outside ocaml's heap

["Gerd Stolpmann" <info@gerd-stolpmann.de>]

Hi William,

this can be made working, and there is already a lot of support in
Ocamlnet (module Netsys_mem, espeically init_value). I'm now using this
all the time for populating shared memory blocks (which need to be outside
the ocaml heap) with normal ocaml values.

In Ocamlnet I'm using simply a bigarray for keeping the reference to the
off-heap memory area (remember, bigarrays are just pointers to C arrays).
This allows it to program the whole algorithm accessing such values in
Ocaml.

A warning though: Experience shows also that this type of programming is
very error-prone, as you always have to take the memory representation of
ocaml values into account.

Gerd


> Dear list,
>
> We are building a cache in ocaml and we're wondering if it would make
> sense
> to store ocaml values outside the reach of the gc. (gc on a 20GB cache
> hangs the process for a second or so).
>
> To run some experiments, we wrote a small library (
> https://github.com/besport/ocaml-everlasting) that exposes two functions,
> get and set.
>
> When inserting a value, we copy recursively the blocs outside of the reach
> of the gc (and put the resulting value in some C array). When getting the
> value, we simply pass the pointer to the copied value to the ocaml code
> (the structure is still coherent and the value is directly usable). We
> also
> wrote an "update" function that compare a new value with the existing
> value
> in cache, to avoid unnecessary memory allocation/deallocation.
>
> It does not seems very stable though, but I don't know if it is a bug in
> the update function or simply because this approach is not reasonable. Do
> you have any thoughts? Is there any clever way to build a large cache in
> an
> ocaml app ?
>
> Thanks in advance for any tips!
>
> Best
>
> William
>
>
> --
> William Le Ferrand
>
> Mobile : (+1) (415) 683-1484
> Web : http://williamleferrand.github.com/
> <http://www.linkedin.com/in/williamleferrand>
>
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-- 
Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
Creator of GODI and camlcity.org.
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