From: Xavier Leroy <Xavier.Leroy@inria.fr>
To: Chris Hecker <checker@d6.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] register_global_root, malloc, etc.
Date: Tue, 14 Aug 2001 10:25:37 +0200 [thread overview]
Message-ID: <20010814102537.A4081@pauillac.inria.fr> (raw)
In-Reply-To: <4.3.2.7.2.20010726013540.027fa990@shell16.ba.best.com>; from checker@d6.com on Thu, Jul 26, 2001 at 01:48:24AM -0700
[I see that your message was left unanswered. Hope the following late
answer will help.]
> If I'm writing a module in C and want to have an abstract type that
> corresponds to that struct (allocated with new/malloc/etc. from C),
> is the following code correct?
>
> CAMLlocal1(result);
> foo *p = new foo;
> p->callback = Val_unit;
> register_global_root(&(p->callback));
> result = alloc_small(1,Abstract_tag);
> Field(result,0) = (value)p;
> CAMLreturn(result);
>
> Then, later, I can just assign another closure passed to a C function (and CAMLparam'ed) to p->callback without worrying about it, like this:
>
> value set_callback( value fooval, value callback )
> {
> CAMLparam2(fooval,callback);
> foo *p = (foo *)Field(fooval,0);
> p->callback = callback;
> CAMLreturn(Val_unit);
> }
>
> Is that correct?
Yes.
> Should I use Custom_tag and register all the finalization functions
> and whatnot for my abstract type, or is Abstract_tag good enough
> assuming I've got a free_foo function that users of the module are
> supposed to call to deallocate the abstract type? free_foo should
> call remove_global_root before deleting the memory, right? But I
> don't need to do anything to explicitly delete the callback or the
> Abstract_tag block that was passed in since the GC will handle it?
You're 100% correct. The only advantage of Custom_tag over
Abstract_tag is that finalization can be handled by the GC instead of
by the user (via free_foo). GC-based finalization is safer in the
sense that you're certain that the object cannot be reached again by
Caml code. With user-managed finalization, there is always the risk
that the program will call free_foo, then still use the "foo" value
afterwards.
- Xavier Leroy
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next prev parent reply other threads:[~2001-08-14 8:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-26 8:48 Chris Hecker
2001-08-14 8:25 ` Xavier Leroy [this message]
2001-08-15 2:26 ` Alexander V. Voinov
2001-08-16 0:59 ` Chris Hecker
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