From: Jess Balint <jbalint@gmail.com>
To: Daniel Colascione <dancol@dancol.org>
Cc: John Wiegley <johnw@gnu.org>, 22737@debbugs.gnu.org
Subject: bug#22737: 25.1; Finalizer should be optional in dynamic modules
Date: Mon, 29 Feb 2016 14:28:14 -0600 [thread overview]
Message-ID: <CA+fD2U2_S+g=DHc_2SMVz+wew+e8sk9ygUE2cu67yyFg88GTEw@mail.gmail.com> (raw)
In-Reply-To: <56D0C9B4.8070105@dancol.org>
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On Fri, Feb 26, 2016 at 3:55 PM, Daniel Colascione <dancol@dancol.org>
wrote:
> On 02/26/2016 01:51 PM, Jess Balint wrote:
> > On Fri, Feb 26, 2016 at 3:33 PM, Eli Zaretskii <eliz@gnu.org
> > <mailto:eliz@gnu.org>> wrote:
> >
> > > Date: Fri, 26 Feb 2016 12:53:20 -0600
> > > From: Jess Balint <jbalint@gmail.com <mailto:jbalint@gmail.com>>
> > > Cc: 22737@debbugs.gnu.org <mailto:22737@debbugs.gnu.org>
> > >
> > > What will happen if such objects are exposed to Lisp, copied or
> > > assigned to other Lisp variables, etc.? Won't this cause all
> kinds of
> > > trouble, like modifying one such object will magically modify
> several
> > > others, which share its storage?
> > >
> > > This is how C code works. If you return a pointer from a function,
> you may have to free that pointer yourself or
> > > you may not. You may get the same pointer back from multiple calls
> to the same function. If you use the
> > > pointer after it's been freed, it's your problem. You need to
> agree with the owner of the pointer how the
> > > memory is to be managed. With pointers, modifications to the
> underlying data are visible by all who have a
> > > pointer to the data. I wouldn't call this "magically modifying
> others".
> >
> > In C, yes. But we are talking about Lisp objects here.
> >
> > Am I the only one who is uneasy with supporting such Lisp objects?
> If
> > so, I will shut up and install the changes. Daniel, John, what's
> your
> > opinion on this?
> >
> > Thanks.
> >
> >
> > All I'm asking for is to allow the code to accept a NULL finalizer. This
> > means no finalizer will be called. It's a clear and simple semantic.
> > Upside is that I (and others who do not want Emacs to free their
> > pointers) will not have to create a no-op function unnecessarily to
> > supply a finalizer to Emacs.
>
> A no-op function is trivial though; creating it forces you to think
> about whether you actually need to free the resulting memory. I think
> it's more important to discourage memory leaks and simplify the
> semantics of the finalizer parameter than to make this rare (I think)
> use case slightly easier for module implementors.
Ok, I can respect that. I don't really agree, but... so be it. If this is
the way you want it to work, maybe make_user_ptr() should return nil.
Otherwise this will lead to segfaults.
Jess
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prev parent reply other threads:[~2016-02-29 20:28 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-18 21:52 bug#22737: 25.1; Finalizer should be optional in dynamic modules Jess Balint
2016-02-19 9:33 ` Eli Zaretskii
2016-02-23 22:47 ` Jess Balint
2016-02-24 3:40 ` Eli Zaretskii
2016-02-26 16:17 ` Jess Balint
2016-02-26 18:36 ` Eli Zaretskii
2016-02-26 18:53 ` Jess Balint
2016-02-26 21:33 ` Eli Zaretskii
2016-02-26 21:51 ` Jess Balint
2016-02-26 21:55 ` Daniel Colascione
2016-02-29 20:28 ` Jess Balint [this message]
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