From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id EAA14765; Wed, 15 Aug 2001 04:28:47 +0200 (MET DST) X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id EAA14770 for ; Wed, 15 Aug 2001 04:28:46 +0200 (MET DST) Received: from str12.sobor.org (adsl-63-198-183-99.dsl.snfc21.pacbell.net [63.198.183.99]) by concorde.inria.fr (8.11.1/8.10.0) with ESMTP id f7F2SiP14163; Wed, 15 Aug 2001 04:28:45 +0200 (MET DST) Received: from quasar.ipa.nw.ru (anza.sobor.org [192.168.123.51]) by str12.sobor.org (Postfix) with ESMTP id 0AFADAEFB7; Tue, 14 Aug 2001 19:19:45 -0700 (PDT) Message-ID: <3B79DDC7.36D40AC3@quasar.ipa.nw.ru> Date: Tue, 14 Aug 2001 19:26:15 -0700 From: "Alexander V. Voinov" Organization: Fear of the Lord is the beginning of wisdom X-Mailer: Mozilla 4.75 [en] (Windows NT 5.0; U) X-Accept-Language: en MIME-Version: 1.0 To: Xavier Leroy Cc: Chris Hecker , caml-list@inria.fr Subject: Re: [Caml-list] register_global_root, malloc, etc. References: <4.3.2.7.2.20010726013540.027fa990@shell16.ba.best.com> <20010814102537.A4081@pauillac.inria.fr> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-caml-list@pauillac.inria.fr Precedence: bulk Hi All, Xavier Leroy wrote: > > [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. I can't understand who will delete `foo *', allocated via `foo *p = new foo'? As I understood from the manual, Custom_tag is the only way to assign free_foo with the resulting Caml object. And I'm surprised by your statement that after calling free_foo the program can still use this reference. This sounds as if I bought a train ticket but the railway station clerk warned me that despite of the fact that I paid there still is a risk that my seat will be sold to somebody else :-). Alexander ------------------- Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr