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Date: Fri, 1 Jun 2001 00:13:01 +0200
From: Daniel de Rauglaudre <daniel.de_rauglaudre@inria.fr>
To: Harry Chomsky <harry@chomsky.net>
Cc: Caml list <caml-list@inria.fr>
Subject: Re: [Caml-list] Win32 API
Message-ID: <20010601001301.A11836@verdot.inria.fr>
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In-Reply-To: <00c301c0ea11$17a38570$22f65140@w2kpro>; from harry@chomsky.net on Thu, May 31, 2001 at 01:34:29PM -0700
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Hi,

On Thu, May 31, 2001 at 01:34:29PM -0700, Harry Chomsky wrote:

> I've embarked on a project to enable writing full-fledged Win32 applications
> using OCaml.  I'm doing this mostly for fun as I take a break between jobs.
> [...]
> http://www.speakeasy.org/~hchomsky/ocaml-win32.html
> [...]
> The main area I'm uncomfortable with is memory management and the section of
> [...]

As far as I read your C code, you are likely to have problems with the
OCaml GC: you risk unexpected Memory Faults or Bus Errors. When you
call an OCaml alloc function, all your variables of type "value" may
point to wrong places. E.g. if you write:

some_function (value x)
{
   value y;
   y = alloc_tuple(2);
   ...
}

The "alloc_tuple" may call the GC: and the GC may move the other OCaml
allocated values. If the parameter x corresponds to a pointer (i.e. not
an integer), its value may become false after the allocation of y (may
or may not). The correct way is to previously inform the GC that it
has to change the value of the variable x if it changes the location
of the values it refers to.

This can (must) be done by the macros defined in the module memory.h.
The correct way (if I am not wrong) to write this function like this:

some_function (value x)
{
   CAMLparam1(x);
   value y;
   y = alloc_tuple(2);
   ...
}

-- 
Daniel de RAUGLAUDRE
daniel.de_rauglaudre@inria.fr
http://cristal.inria.fr/~ddr/
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