From: John Carr <jfc@mit.edu>
To: caml-list@inria.fr
Subject: Re: [Caml-list] Interfacing with C: bad practice
Date: Tue, 16 Aug 2011 10:27:33 -0400 [thread overview]
Message-ID: <201108161427.p7GERXUo011092@outgoing.mit.edu> (raw)
In-Reply-To: <20110816103929.GB3772@NANA.localdomain>
Mauricio Fernandez <mfp@acm.org> wrote:
> This has been in my mind for a while: why don't CAMLparamX declare the local
> variables as volatile?
That would not help.
Passing the address of a local variable to an external function
warns the compiler that the variable may change when another
external function is called. That is necessary and sufficient
to accomodate OCaml's garbage collector.
The problem here is, order of evaluation of function call arguments
is unspecified.
In principle the same bug is present in
Field(camlvar, 1) = allocating_function(...);
camlvar may be evaluated before the allocating function is called,
and the allocating function may move the object it points to.
I don't know whether the new C sequencing rules change this, but I
wouldn't intentionally write code that depends on the ordering of
this statement.
--John Carr (jfc@mit.edu)
next prev parent reply other threads:[~2011-08-16 14:27 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-16 7:37 Dmitry Bely
2011-08-16 8:04 ` Török Edwin
2011-08-16 8:25 ` Dmitry Bely
2011-08-16 8:43 ` Török Edwin
2011-08-16 9:46 ` rixed
2011-08-16 9:53 ` Dmitry Bely
2011-08-16 10:17 ` Török Edwin
2011-08-16 11:04 ` rixed
[not found] ` <20110816.105738.246515733851238101.Christophe.Troestler@umons.ac.be>
2011-08-16 9:21 ` Dmitry Bely
2011-08-16 10:39 ` Mauricio Fernandez
2011-08-16 14:27 ` John Carr [this message]
2011-08-16 12:28 ` [Caml-list] " Dmitry Bely
2011-08-16 15:25 ` [Caml-list] " Richard W.M. Jones
2011-08-16 15:51 ` rixed
2011-08-16 16:00 ` Will M. Farr
2011-08-16 16:10 ` Richard W.M. Jones
2011-08-16 16:17 ` Richard W.M. Jones
2011-08-16 16:18 ` Dmitry Bely
2011-08-16 16:22 ` Richard W.M. Jones
2011-08-16 16:27 ` Richard W.M. Jones
2011-08-16 16:30 ` malc
2011-08-16 16:34 ` Török Edwin
2011-08-16 16:47 ` Richard W.M. Jones
2011-08-16 16:55 ` [Caml-list] " Jeffrey Scofield
2011-08-16 17:08 ` Will M. Farr
2011-08-16 19:46 ` Gerd Stolpmann
2011-08-16 20:18 ` Jeffrey Scofield
2011-08-16 17:08 ` [Caml-list] " rixed
2011-08-16 16:06 ` John Carr
2011-08-16 16:14 ` Wojciech Meyer
2011-08-16 16:13 ` Dmitry Bely
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