[ANNOUNCE] GtkUnique 0.1.0 - Single Instance Application library

[Emmanuele Bassi <ebassi gmail com>]

Hi all;

For the Google Summer of Code, Vytas Liuolia[1] wrote the (very much
needed) guniqueapp library[2]; just a small recap: libguniqueapp allows
the creation of single instance applications[3], that is applications
that gets instanced once and each subsequent instance just quits - or
send a command to the currently running instance.

Libguniqueapp has two available backends: D-Bus, as default, and bacon
(a Un*x socket living in /tmp and used to send and receive commands).
After reading about guniqueapp on desktop-devel-list, I began hacking on
it in order to add a new backend, using X itself as an IPC mechanism.

Single instance applications are used on the desktop (Gedit, Mozilla,
Epiphany, Evince - the list goes on), but are very interesting for an
embedded device because of the the memory and/or screen real estate
limitations.  On the Maemo platform, for instance, this issue has been
solved by having each application behave as a D-Bus service: each time
an application is launched a new object on the bus is created and
subsequent instances just abort.  Not every embedded platform uses (or
can use) D-Bus, though, hence the need for anothe IPC mechanism - like
the Xlibs-based backend.

Unfortunately, hacking on libguniqueapp required pretty much the rewrite
of the whole build environment; the current code base needed some
cleaning up and some new feature I intended to add required a revision
of the whole IPC protocol.  Thus, I preferred to create a whole new
library from scratch, called GtkUnique, but keeping the API pretty much
the same.

The differences from GtkUnique pretty much are:

  * the backend implementations have been more cleanly separated and
    hidden in helper libraries;
  * there's an Xlibs-based backend, which is preferred right after the
    D-Bus backend;
  * the IPC channel is bidirectional; that is: the message sent from a
    second instance to the first instance of the application has a
    return code, in case the operation that has been requested failed;
  * the D-Bus backend has been changed: the name of the application is
    used as the object on the bus, so you don't have awkward stuff like 
    org.gnome.GUniqueApp.YourApp but something a bit more friendly like
    org.gnome.YourApp (implementing the org.gtk.UniqueApp interface and
    the object path is /Factory);
  * also in the D-Bus backend, the SendMessage message has been changed:
    it now accepts a stringified command, which is the "nick" value of
    the GtkUniqueCommand enum object; this way you can send commands
    like 'activate' or 'new' instead of integers on the wire, in case
    you want to implement the D-Bus backend from scratch.
  * the GtkUniqueApp object keeps track of the top-level windows of the
    application (needed for the Xlibs backend, doesn't hurt on the
    other backends);
  * I've added API documentation using gtk-doc;
  * Perl and Python bindings are in the works;

You may think of GtkUnique as a fork of libguniqueapp; really, it's more
of an experiment I wrote to get more aquainted with Xlibs and D-Bus
programming.  I intend to use GtkUnique inside the next release of the
Dictionary and inside another couple projects of mine, so I'll keep on
working on it.

If you want to play with it, just pull the bazaar repository from here:

  * main trunk:    bzr branch http://o-hand.com/~ebassi/bzr/gtkunique
  * perl bindings: bzr branch http://o-hand.com/~ebassi/bzr/gtkunique-perl

and there's a tarball available here:

  http://o-hand.com/~ebassi/gtkunique-0.1.0.tar.gz

Note on the library: the libbacon-like backend is broken at the moment,
as I'm still playing with it.

Note on the bindings: I'll add the branch for the python bindings as
soon as I have them in a buildable state.  The Perl bindings are very
rough at the moment - the "make test" phase fails and while you can send
a message from a Perl application to a C application sharing the same
name, you can't do the opposite.

+++

[1] http://blogs.gnome.org/view/newren/2006/08/09/1
[2] http://guniqueapp.akl.lt
[3] http://live.gnome.org/SingleInstanceApps

Ciao,
 Emmanuele.

-- 
Emmanuele Bassi,  E: ebassi gmail com
W: http://www.emmanuelebassi.net
B: http://log.emmanuelebassi.net