Re: [Caml-list] Concurrent/parallel programming

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

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Am Mittwoch, den 08.01.2014, 11:55 +0000 schrieb Mark Shinwell:
> On 8 January 2014 11:36, Gerd Stolpmann <info@gerd-stolpmann.de> wrote:
> > There is a workaround in place - so far the OS supports it: thanks to
> > Xavier the symbols caml_modify and caml_initialize are declared as weak
> > in 4.01, allowing them to be redefined in executables. Netmulticore
> > redefines these symbols with their pre-4.01 functions.
> >
> > This isn't optimal yet, because the old write barriers are a bit slower,
> > and because this introduces a very low-level dependency on the current
> > version of Ocaml. Nevertheless, it works for now. (Ideas for a better
> > solution are highly welcome.)
> 
> Jeremie Dimino and myself have a somewhat embryonic proposal
> that should permit most of the write barrier to be
> circumvented for out-of-heap access, and also avoid the page
> table test.  We'll send mail to the list in due course once
> we've had time to think about this further.

I'm very curious to hear about that.

So far I have only the idea to override the := operator selectively in
all modules that want to modify out-of-heap values:

let ( := ) = Netmcore_heap.assign h

where Netmcore_heap.assign is a C function that tests whether the
destination address is in the out-of-heap address space of h. If so, the
assignment can be done directly. If not, it just falls back to a normal
caml_modify.

This solution isn't nice, though, because it can be very problematic to
have the extra indirection of ref. So, what I'm searching for is a way
to turn any record mutation into an external C function call (or at
least to parametrize the write barrier somehow).

Gerd

> Mark
> 

-- 
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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
Creator of GODI and camlcity.org.
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
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