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Date: Thu, 22 Sep 2005 20:33:14 +0200
From: Lukasz Stafiniak <lukstafi@gmail.com>
Reply-To: Lukasz Stafiniak <lukstafi@gmail.com>
To: Dominik Brugger <dominikbrugger@gmx.de>
Subject: Re: [Caml-list] Re: Ocaml C interface - Usage of custom blocks
Cc: caml-list@yquem.inria.fr,
	Dominik Brugger <dominikbrugger@fastmail.fm>
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2005/9/22, Dominik Brugger <dominikbrugger@gmx.de>:
> Is there a "best practice" for returning C data to OCaml
> which was allocated by malloc?
>

My bet is on custom blocks.

> But section 18.2.3 of the manual points out, that it is potentially
> dangerous to free C data, as it might be reclaimed by the OCaml GC.

No. It is dangerous to free C data, because you might still use them
on the OCaml side. GC will not reclaim "malloc pointers".

> So what happens if the data is never explicitly freed? Does the OCaml hea=
p
> space grow until there is no more memory available to the C part of the
> OCaml program?

The data (allocated by malloc) is not on OCaml heap. You have memory
leak on the C side.
>
> In my opinion the only way to avoid these problems is the usage of
> OCaml custom blocks.

My too. The difficulty comes, when the data is also refered by other C
data structures. I've solved it by reference counters, decremented
explicitly on C side and by finalisation on OCaml side.

Lukasz