Name

GTypePlugin — An interface for dynamically loadable types.

Library

gobject.lib

Synopsis

#include <glib-object.h>

             GTypePlugin;
             GTypePluginClass;
void        (*GTypePluginUse)                       (GTypePlugin *plugin);
void        (*GTypePluginUnuse)                     (GTypePlugin *plugin);
void        (*GTypePluginCompleteTypeInfo)          (GTypePlugin *plugin, GType g_type, GTypeInfo *info, 
                                                     GTypeValueTable *value_table);
void        (*GTypePluginCompleteInterfaceInfo)     (GTypePlugin *plugin, GType instance_type, GType interface_type, 
                                                     GInterfaceInfo *info);
void        g_type_plugin_use                       (GTypePlugin *plugin);
void        g_type_plugin_unuse                     (GTypePlugin *plugin);
void        g_type_plugin_complete_type_info        (GTypePlugin *plugin, GType g_type, GTypeInfo *info, 
                                                     GTypeValueTable *value_table);
void        g_type_plugin_complete_interface_info   (GTypePlugin *plugin, GType instance_type, GType interface_type, 
                                                     GInterfaceInfo *info);

Detailed Description

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

The type is initially introduced (usually upon loading the module the first time, or by the main application that knows what modules introduces what types), like this: 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.
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.
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.
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).
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.
Things may repeat from the second step.

To implement a GTypePlugin type that carries a use_count, once use_count goes from zero to one, 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, 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.

Object Hierarchy

  GInterface
   +----GTypePlugin

Known Implementations

GTypePlugin is implemented by GTypeModule.

Details

GTypePlugin

typedef struct _GTypePlugin GTypePlugin;

The GTypePlugin typedef is used as a placeholder for objects that implement the GTypePlugin interface.

GTypePluginClass

typedef struct {
  GTypePluginUse		   use_plugin;
  GTypePluginUnuse		   unuse_plugin;
  GTypePluginCompleteTypeInfo	   complete_type_info;
  GTypePluginCompleteInterfaceInfo complete_interface_info;
} GTypePluginClass;

The GTypePlugin interface is used by the type system in order to handle the lifecycle of dynamically loaded types.

GTypePluginUse `use_plugin`;	Increases the use count of the plugin.
GTypePluginUnuse `unuse_plugin`;	Decreases the use count of the plugin.
GTypePluginCompleteTypeInfo `complete_type_info`;	Fills in the GTypeInfo and GTypeValueTable structs for the type. The structs are initialized with `memset(s, 0, sizeof (s))` before calling this function.
GTypePluginCompleteInterfaceInfo `complete_interface_info`;	Fills in missing parts of the GInterfaceInfo for the interface. The structs is initialized with `memset(s, 0, sizeof (s))` before calling this function.

GTypePluginUse ()

void     (*GTypePluginUse)          (GTypePlugin *plugin);

The type of the use_plugin function of GTypePluginClass, which gets called to increase the use count of plugin.

plugin : the GTypePlugin whose use count should be increased

GTypePluginUnuse ()

void     (*GTypePluginUnuse)       (GTypePlugin *plugin);

The type of the unuse_plugin function of GTypePluginClass.

plugin : the GTypePlugin whose use count should be decreased

GTypePluginCompleteTypeInfo ()

void    (*GTypePluginCompleteTypeInfo)      (GTypePlugin *plugin, GType g_type, GTypeInfo *info, GTypeValueTable *value_table);

The type of the complete_type_info function of GTypePluginClass.

`plugin` :	the GTypePlugin
`g_type` :	the GType whose info is completed
`info` :	the GTypeInfo struct to fill in
`value_table` :	the GTypeValueTable to fill in

GTypePluginCompleteInterfaceInfo ()

void   (*GTypePluginCompleteInterfaceInfo)   (GTypePlugin *plugin, GType instance_type, GType interface_type, 
                                              GInterfaceInfo *info);

The type of the complete_interface_info function of GTypePluginClass.

`plugin` :	the GTypePlugin
`instance_type` :	the GType of an instantiable type to which the interface is added
`interface_type` :	the GType of the interface whose info is completed
`info` :	the GInterfaceInfo to fill in

g_type_plugin_use ()

void     g_type_plugin_use    (GTypePlugin *plugin);

Calls the use_plugin function from the GTypePluginClass of plugin. There should be no need to use this function outside of the GObject type system itself.

plugin : a GTypePlugin

g_type_plugin_unuse ()

void    g_type_plugin_unuse    (GTypePlugin *plugin);

Calls the unuse_plugin function from the GTypePluginClass of plugin. There should be no need to use this function outside of the GObject type system itself.