Re: DBus GLib API

["James Henstridge" <james jamesh id au>]

On 14/02/07, Rob Taylor <rob taylor codethink co uk> wrote:
> Rob Taylor wrote:
> > (Changing subject appropriately, should have done this earlier..)
> >
> > Havoc Pennington wrote:
> >> Parallel install will be of limited value most likely if any *libraries*
> >> in the typical GNOME/GTK stack use dbus-glib, because you'll probably
> >> still use some of the same symbol names. That is, as soon as a lib in
> >> the stack uses a dbus-glib ABI, that ABI is locked in.
> >>
> >> You might address this by strongly discouraging such a dependency in
> >> several places online and in the docs, or something, if changing ABI
> >> looks necessary.
> >
> > Hmm, there's a *lot* of libraries using dbus-glib-1 right now (13 on
> > Ubuntu Edgy, according to apt-cache rdepends). The aim would be to allow
> > us to break ABI at will without disturbing these current users. I guess
> > the right thing is to go to dbus-glib-2.
>
> To be clear - the solution I'm suggesting is to have the API version in
> the library name, like gtk+ or gstreamer. We could just as well go to
> dbus-glib-1.1 or dbus-glib-2. Personally I rather like the way Gstreamer
> does it: major.minor, with minor being odd signifying that its an
> unstable API.

The problem here isn't the naming of the library.  The problem is if
something like the following occurs:
* Some application links to both libfoo and libbar
* libfoo adds a dependency on dbus-glib-X
* libbar adds a dependency on dbus-glib-Y

Now the application is linked to both dbus-glib-X and dbus-glib-Y.  If
the two versions of dbus-glib share any symbols, then you will get
undefined results (since with ELF, libfoo and libbar will be linking
to the dbus-glib symbols by name, rather than binding to the
particular version they link with).  For platforms where the ELF
linking is not a problem, you'd still get into trouble if the two
versions of dbus-glib tried to register GTypes with the same name.

So while having parallel installable dbus-glib versions is okay for
applications to use, it'll be a nightmare if libraries that are part
of the Gnome platform depend on different versions.

James.