|Subject:||bug#22737: 25.1; Finalizer should be optional in dynamic modules|
|Date:||Mon, 29 Feb 2016 14:28:14 -0600|
On 02/26/2016 01:51 PM, Jess Balint wrote:
> On Fri, Feb 26, 2016 at 3:33 PM, Eli Zaretskii <address@hidden
> <mailto:address@hidden>> wrote:
> > Date: Fri, 26 Feb 2016 12:53:20 -0600
> > From: Jess Balint <address@hidden <mailto:address@hidden>>
> > Cc: address@hidden <mailto:address@hidden>
> > 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?
> 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.
|[Prev in Thread]||Current Thread||[Next in Thread]|