Type Modules

This example shows you how to implement a GLib.TypeModule based plugin in Vala. It also shows the usage of static construct/destruct block.

// plugin.vala
public class MyClass : Object
{
        static construct
        {
                message("MyClass init");
        }

        static ~MyClass()
        {
                message("MyClass deinit");
        }
}

[ModuleInit]
Type plugin_init(GLib.TypeModule type_modul)
{
        return typeof(MyClass);
}

// loader.vala
class MyModule : TypeModule
{
      [CCode (has_target = false)]
      private delegate Type PluginInitFunc(TypeModule module);

      private GLib.Module module = null;

      private string name = null;

      public MyModule(string name)
      {
               this.name = name;
      }

      public override bool load()
      {
               string path = Module.build_path(null, name);
               module = Module.open(path, GLib.ModuleFlags.BIND_LAZY);
               if(null == module) {
                        error("Module not found");
               }

               void * plugin_init = null;
               if(! module.symbol("plugin_init", out plugin_init)) {
                        error("No such symbol");
               }

               ((PluginInitFunc) plugin_init)(this);

               return true;
      }

      public override void unload()
      {
               module = null;

               message("Library unloaded");
      }
}

// Never unref instance of GTypeModule
// http://www.lanedo.com/~mitch/module-system-talk-guadec-2006/Module-System-Talk-Guadec-2006.pdf
static TypeModule module = null;

int main()
{
      module = new MyModule("plugin");
      module.load();

      var o = GLib.Object.new(Type.from_name("MyClass"));

      // free last instance, plugin unload
      o = null;

      return 0;
}

Build:

$ valac -o loader loader.vala --pkg=gmodule-2.0
$ valac --ccode plugin.vala
$ gcc -fPIC -shared -o libplugin.so plugin.c $(pkg-config --libs --cflags gobject-2.0 gmodule-2.0)

Run:

$ LD_LIBRARY_PATH=$PWD ./loader

Which should output something like this:

** Message: plugin.vala:5: MyClass init
** Message: plugin.vala:10: MyClass deinit
** Message: loader.vala:37: Library unloaded