The GObject type system supports dynamic loading of types. The TypePlugin interface is used to handle the lifecycle of dynamically loaded types. It goes as follows:

1. The type is initially introduced (usually upon loading the module the first time, or by your main application that knows what modules introduces what types), like this:

C code

  new_type_id = g_type_register_dynamic (parent_type_id,
                                         "TypeName",
                                         new_type_plugin,
                                         type_flags);
  

where newTypePlugin is an implementation of the TypePlugin interface.

1. The type's implementation is referenced, e.g. through typeClassRef or through g_type_create_instance() (this is being called by g_object_new()) or through one of the above done on a type derived from newTypeId.
2. This causes the type system to load the type's implementation by calling typePluginUse and typePluginCompleteTypeInfo on newTypePlugin.
3. At some point the type's implementation isn't required anymore, e.g. after typeClassUnref or typeFreeInstance (called when the reference count of an instance drops to zero).
4. This causes the type system to throw away the information retrieved from typePluginCompleteTypeInfo and then it calls typePluginUnuse on newTypePlugin.
5. Things may repeat from the second step.

So basically, you need to implement a TypePlugin type that carries a use_count, once use_count goes from zero to one, you need to load the implementation to successfully handle the upcoming typePluginCompleteTypeInfo call. Later, maybe after succeeding use/unuse calls, once use_count drops to zero, you can unload the implementation again. The type system makes sure to call typePluginUse and typePluginCompleteTypeInfo again when the type is needed again.

TypeModule is an implementation of TypePlugin that already implements most of this except for the actual module loading and unloading. It even handles multiple registered types per module.