On Fri, May 25, 2018 at 09:13:51AM +0200, Andrea Bolognani wrote:
> On Wed, 2018-05-23 at 18:05 +0200, Pavel Hrdina wrote:
> > I liked the way how GLib is solving the issue so we can simply use the
> > same approach since it looks reasonable.
> >
> > There would be three different macros that would be used to annotate
> > variable with attribute cleanup:
> >
> > VIR_AUTOFREE char *str = NULL;
> >
> > - this would call virFree on that variable
> >
> > VIR_AUTOPTR(virDomain) domain = NULL;
> >
> > - this would call registered free function on that variable
> > - to register the free function you would use:
> >
> > VIR_DEFINE_AUTOPTR_FUNC(virDomain, virDomainFree);
> >
> > VIR_AUTOCLEAR(virDomain) domain = { 0 };
> >
> > - this would call registered clear function to free the content of
> > that structure
> > - to register that clear function you would use:
> >
> > VIR_DEFINE_AUTOCLEAR_FUNC(virDomain, virDomainClear);
>
> I assume you would get a compilation error when trying to eg. use
> VIR_AUTOCLEAR() with a type that doesn't have a clear function
> registered?
Yes, because the macro would call non existing function.
> As for VIR_AUTOFREE() and VIR_AUTOPTR(), I'd very much prefer if we
> could have a single macro, since from the high-level point of view
> they're both doing the same thing, that is, freeing memory that was
> allocated on the heap.
It would be nice but I don't think it's worth it.
> 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:
GLib libvirt
g_autofree VIR_AUTOFREE
g_autoptr VIR_AUTOPTR
g_auto VIR_AUTOCLEAR
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.
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.
Pavel
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