Re: [Libguestfs] GObject bindings overview

On Fri, Jan 20, 2012 at 12:07:47PM +0000, Matthew Booth wrote: > There are a couple of points in here I'm still not 100% happy with. > Specifically the handling of FBuffer and the Cancellable flag. Both > are explained below. I'm interested in suggestions. > A parallel struct is created for each libguestfs struct type. A > boxed type is created for each parallel struct. It's field types are > all mapped trivially to gobject basic types (e.g. gchar *, gint32) > except FBuffer. FBuffer is mapped as: > > guint8 *<field> > guint32 <field>_size > > Unfortunately I can see no way to attach annotation to these fields, > so the bindings do not appreciate that these fields are related. I'm > not happy with this at all, so I may try manual tweaking of the .gir > to see if we can turn these into a single returned array where > possible. Those two fields look just like GByteArray struct GByteArray { guint8 *data; guint len; }; Can you just outpout that - I expect bindings will already know how to deal with that. > Cancellation: > ************* > > Certain apis are cancellable. These all take a GCancellable as the > final argument before GError **. This can be passed NULL if > cancellation is not required. While I have written cancellation, I > have not yet tested it *at all* other than it compiles and works > correctly when NULL is passed in. > > We recently made Cancellable an explicit flag whereas before it was > implicit if the api had a FileIn or FileOut argument. This means it > is now possible to break the GObject api without breaking the C api > with the addition of a Cancellable flag. What potential solutions > are there to this problem? I can see: > > • Live with breaking the GObject api if it ever comes up. > • Never add Cancellable to an existing api. > • Automatically add a GCancellable argument to all GObject apis, > just in case. I think option 2 is the only long term viable approach. If any existing APIs needs to be made cancellable, then define a new API that is the same, but with the cancellable flag set.