GObjectTypePlugin

An interface that handles the lifecycle of dynamically loaded types.

The GObject type system supports dynamic loading of 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 new_type_id = g_type_register_dynamic (parent_type_id, "TypeName", new_type_plugin, type_flags); where new_type_plugin is an implementation of the GTypePlugin interface.

2. The type’s implementation is referenced, e.g. through g_type_class_ref() 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 new_type_id.

3. This causes the type system to load the type’s implementation by calling g_type_plugin_use() and g_type_plugin_complete_type_info() on new_type_plugin.

4. At some point the type’s implementation isn’t required anymore, e.g. after g_type_class_unref() or g_type_free_instance() (called when the reference count of an instance drops to zero).

5. This causes the type system to throw away the information retrieved from g_type_plugin_complete_type_info() and then it calls g_type_plugin_unuse() on new_type_plugin.

6. Things may repeat from the second step.

So basically, you need to implement a GTypePlugin 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 g_type_plugin_complete_type_info() 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 g_type_plugin_use() and g_type_plugin_complete_type_info() again when the type is needed again.

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