[libvirt] [GSoC] Design ideas for implementing cleanup attribute

[Andrea Bolognani]

On Fri, 2018-05-25 at 10:04 +0200, Pavel Hrdina wrote:
> On Fri, May 25, 2018 at 09:13:51AM +0200, Andrea Bolognani wrote:
> > However, I realize it might not be possible to register free
> > functions for a native type without having to introduce something
> > like
> > 
> >   typedef char * virString;
> > 
> > thus causing massive churn. How does GLib deal with that?
> 
> If you would look into GLib documentation you would see that this
> design basically copies the one in GLib:

Sorry, I should have looked up the documentation and implementation
before asking silly questions. Guess the morning coffee hadn't quite
kicked in yet :/

>     GLib                libvirt
> 
>     g_autofree          VIR_AUTOFREE
>     g_autoptr           VIR_AUTOPTR
>     g_auto              VIR_AUTOCLEAR

For what it's worth, I think VIR_AUTOCLEAR is a much better name
than g_auto :)

> In GLib you are using them like this:
> 
> g_autofree char *string = NULL;
> g_autoptr(virDomain) dom = NULL;
> g_auto(virDomain) dom = { 0 };
> 
> So yes it would require to introduce a lot of typedefs for basic types
> and that is not worth it.

I'm not sure we would need so many typedefs, but there would
certainly be a lot of churn involved.

Personally, I'm not so sure it wouldn't be worth the effort,
but it's definitely something that we can experiment with it at
a later time instead of holding up what's already a pretty
significant improvement.

> In libvirt we would have:
> 
> VIR_AUTOFREE char *string = NULL;
> VIR_AUTOPTR(virDomainPtr) dom = NULL;
> VIR_AUTOCLEAR(virDomain) dom = { 0 };
> 
> If you notice the difference, in libvirt we can use virDomainPtr
> directly because we have these typedefs, in GLib macro
> G_DEFINE_AUTOPTR_CLEANUP_FUNC creates similar typedef.

While I'm not a fan of our *Ptr typedefs in general, I guess this
time I'm glad we have them because VIR_AUTOPTR() doesn't hide the
fact that what you're declaring is a pointer; that is, the macro
argument is also exactly the type of the variable.

-- 
Andrea Bolognani / Red Hat / Virtualization