java-gnome 4.0.2 released!

This blog post is the release note from the NEWS file which you can read online … or in the sources, of course!


java-gnome 4.0.2 (12 Feb 2007)

The End of the Beginning!

Major bugfixes and refactorings

Setting and getting properties on GObjects requires some tricky manoeuvring. We implemented the code to do this early on, and it looked like our general mechanism for getting Proxy instances for arbitrary pointers was working fine for properties. It turns out, however, that when you call g_type_name() on a GValue containing a GObject, it returns the name of the type that was listed when the property specification was registered, rather than saying it is a GValue (as you might expect) or what the object actually is (that you might also reasonably expect).

This led to all kinds of nastiness since the type name was what we were using in our instanceFor() mechanism to discriminate (on the Java side) what kind of Proxy subclass to create. The example we tripped over was asking for the parent property of a Button packed into a VBox. What g_type_name() told us was “GtkContainer”, not “GtkVBox”! And that was a big problem, because Container is abstract, and besides, we want to instantiate a concrete VBox Proxy, not a Container one!

The solution basically boiled down to having two separate code paths: one named objectFor() [a greatly simplified version of the previous instanceFor()] which returns normal Proxy objects for GObject subclasses (Buttons and Labels and whatnot), and a new code path available via valueFor() to specifically return our GValue Proxy for the cases where we know we’re getting a GValue back. Since that occurs in limited and known circumstances only (ie, when we’re getting properties) it’s no problem to know which to use when.

Thanks to Davyd Madeley for extensive debugging assistance, and credit to Manish Singh, James Henstridge, and Malcolm Tredinnick for having analyzed the root cause issue and having clarified that two code paths would indeed be necessary.

As often happens when you kick a stone loose, we were able to do a number of refactorings to clean things up. This eventually led to the realization (ok, epiphany) that our treatment of the GValue mechanism was needlessly complex. Toss. We no longer have individual Value subclasses for each different fundamental type, but rather just leave them as opaque references.

This allowed a further simplification of the valueFor() mechanism and even more smashing about in Plumbing with a chainsaw. Net result was a reduction by several hundred lines of code. Yeay!

All of these changes were confined to the internals of the binding machinery and are not user visible.

Loading .glade files

User interface designers are nothing new, but one of the really cool things about GTK has long been the existence of libglade. It’s a library which takes the output of a one of the GNOME user interface designers (such as such as Glade 3 or Gazpacho) and dynamically, at runtime, generates live Windows full of Widgets!

With the arbitrary Proxy retrieval sorted out, the beginnings of a binding of libglade was possible. None of the fancy stuff is there yet, but a .glade file can be loaded, and Widgets retrieved from the instantiated tree.

The JavaDoc for these classes clearly indicates that this is preliminary and subject to change. It may well all be blown away when GtkBuilder lands. We’ll see.

Testing framework

We’ve introduced the beginnings of a unit test framework. At the moment, this just evaluates various getters and setters without doing anything that requires the main loop. Despite this, the unit tests end up exercising the entire Proxy system discussed above; validating that the properties set and get and that the correct Proxy object is returned through a round trip is no mean feat.

You can run the suite from Eclipse, by specifying a JUnit 3 launcher on class UnitTests in the default package in tests/java, or by running

$ make test

the command line.

Further coverage

This release also sees the addition of FileChooser, FileChooserButton, FileChooserDialog etc. This is significant because GtkFileChooser is an interface in GTK, and GtkFileChooserButton implements it. We’d been putting off the question of dealing with GInterface (would it work or be a major problem?) for a while now. We were delighted to find that the design implied by the re-engineered bindings handled it cleanly, elegantly, and without any fuss. Another nice validation of our new architecture.

Finally, a number of new signals were exposed on Widget though these were mostly the result of doing live demonstrations at conferences of how easy extending the coverage of the new bindings is.

Memory management

We have successfully implemented full GObject memory management in java-gnome 4.0 using GLib’s ToggleRef mechanism.

A strongly referenced Java Proxy will not allow its GObject to be destroyed out from underneath it; meanwhile, as long as the GObject is still referenced by something other than java-gnome, an otherwise only weakly reachable Java object that Proxies it will not be finalized. When the situation does occur whereby the GObject is only referenced from java-gnome, and the Java object is no longer strongly referenced by any other Java objects, then the Java object can be garbage collected and the GObject will be unref()’d and destroyed.

You can watch the reference system in action if you set Debug.MEMORY_MANAGEMENT to true.

Huge thanks go to Vreixo Formoso Lopes who collaborated on the design, reviewed the implementation, and contributed test case code.

Build system improvements

A better detection of jni.h is done on Ubuntu, thanks to Michael Kedzierski. This makes java-gnome more likely to build out of the box on Debian-derived systems.

On the eve of release, Srichand Pendyala noticed that if you are running such a system, a package named libglade-dev needs to be installed. Of course, on more modern systems all the necessary dependencies are present merely by having GNOME installed in the first place. We’ll add a check for this Debian specific behaviour in 4.0.3.

The VERSION and APIVERSION constants were moved to org.gnome.gtk.Version so that anyone working on the Gtk main class isn’t forced to do a re-configuration every time they save.

Installation and Packaging

java-gnome 4.0 now has the standard make install command, and the equally standard --prefix option to ./configure.

$ ./configure --prefix=/usr
$ make
$ sudo make install

The install target understands the DESTDIR variable used by packagers to install to a specified prefix within a temporary directory.

See the README file for details.


The feature additions described above were done to bring java-gnome up to speed for the GTK & GNOME tutorial given at linux.conf.au. With that past, we’re not going to do any more manual mockups of code in what will be the generated layers. Focus now turns to designing and implementing the tool that will parse .defs files and output the translation code.

And so my firm returns to focusing on securing the funding needed to develop the project. Once more into the breach! When we succeed, the code generator will be our top priority and shouldn’t take more than a couple months to complete.

You can download java-gnome from ftp.gnome.org or clone a branch from mainline in our DVCS.

AfC