GLib.TypeModule based Plugin in Vala

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 itself: 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);
}

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


Vala/Examples

Projects/Vala/TypeModuleSample (last edited 2013-11-22 16:48:25 by WilliamJonMcCann)