gobject/gtypeplugin.c

   1 /* GObject - GLib Type, Object, Parameter and Signal Library
   2  * Copyright (C) 2000 Red Hat, Inc.
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General
  15  * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include "config.h"
  19
  20 #include "gtypeplugin.h"
  21
  22
  23 /**
  24  * SECTION:gtypeplugin
  25  * @short_description: An interface for dynamically loadable types
  26  * @see_also: #GTypeModule and g_type_register_dynamic().
  27  * @title: GTypePlugin
  28  *
  29  * The GObject type system supports dynamic loading of types.
  30  * The #GTypePlugin interface is used to handle the lifecycle
  31  * of dynamically loaded types. It goes as follows:
  32  *
  33  * 1. The type is initially introduced (usually upon loading the module
  34  *    the first time, or by your main application that knows what modules
  35  *    introduces what types), like this:
  36  *    |[<!-- language="C" -->
  37  *    new_type_id = g_type_register_dynamic (parent_type_id,
  38  *                                           "TypeName",
  39  *                                           new_type_plugin,
  40  *                                           type_flags);
  41  *    ]|
  42  *    where @new_type_plugin is an implementation of the
  43  *    #GTypePlugin interface.
  44  *
  45  * 2. The type's implementation is referenced, e.g. through
  46  *    g_type_class_ref() or through g_type_create_instance() (this is
  47  *    being called by g_object_new()) or through one of the above done on
  48  *    a type derived from @new_type_id.
  49  *
  50  * 3. This causes the type system to load the type's implementation by
  51  *    calling g_type_plugin_use() and g_type_plugin_complete_type_info()
  52  *    on @new_type_plugin.
  53  *
  54  * 4. At some point the type's implementation isn't required anymore,
  55  *    e.g. after g_type_class_unref() or g_type_free_instance() (called
  56  *    when the reference count of an instance drops to zero).
  57  *
  58  * 5. This causes the type system to throw away the information retrieved
  59  *    from g_type_plugin_complete_type_info() and then it calls
  60  *    g_type_plugin_unuse() on @new_type_plugin.
  61  *
  62  * 6. Things may repeat from the second step.
  63  *
  64  * So basically, you need to implement a #GTypePlugin type that
  65  * carries a use_count, once use_count goes from zero to one, you need
  66  * to load the implementation to successfully handle the upcoming
  67  * g_type_plugin_complete_type_info() call. Later, maybe after
  68  * succeeding use/unuse calls, once use_count drops to zero, you can
  69  * unload the implementation again. The type system makes sure to call
  70  * g_type_plugin_use() and g_type_plugin_complete_type_info() again
  71  * when the type is needed again.
  72  *
  73  * #GTypeModule is an implementation of #GTypePlugin that already
  74  * implements most of this except for the actual module loading and
  75  * unloading. It even handles multiple registered types per module.
  76  */
  77
  78
  79 /* --- functions --- */
  80 GType
  81 g_type_plugin_get_type (void)
  82 {
  83   static GType type_plugin_type = 0;
  84
  85   if (!type_plugin_type)
  86     {
  87       const GTypeInfo type_plugin_info = {
  88         sizeof (GTypePluginClass),
  89         NULL,           /* base_init */
  90         NULL,           /* base_finalize */
  91       };
  92
  93       type_plugin_type = g_type_register_static (G_TYPE_INTERFACE, g_intern_static_string ("GTypePlugin"), &type_plugin_info, 0);
  94     }
  95
  96   return type_plugin_type;
  97 }
  98
  99 /**
 100  * g_type_plugin_use:
 101  * @plugin: a #GTypePlugin
 102  *
 103  * Calls the @use_plugin function from the #GTypePluginClass of
 104  * @plugin.  There should be no need to use this function outside of
 105  * the GObject type system itself.
 106  */
 107 void
 108 g_type_plugin_use (GTypePlugin *plugin)
 109 {
 110   GTypePluginClass *iface;
 111
 112   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 113
 114   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 115   iface->use_plugin (plugin);
 116 }
 117
 118 /**
 119  * g_type_plugin_unuse:
 120  * @plugin: a #GTypePlugin
 121  *
 122  * Calls the @unuse_plugin function from the #GTypePluginClass of
 123  * @plugin.  There should be no need to use this function outside of
 124  * the GObject type system itself.
 125  */
 126 void
 127 g_type_plugin_unuse (GTypePlugin *plugin)
 128 {
 129   GTypePluginClass *iface;
 130
 131   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 132
 133   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 134   iface->unuse_plugin (plugin);
 135 }
 136
 137 /**
 138  * g_type_plugin_complete_type_info:
 139  * @plugin: a #GTypePlugin
 140  * @g_type: the #GType whose info is completed
 141  * @info: the #GTypeInfo struct to fill in
 142  * @value_table: the #GTypeValueTable to fill in
 143  *
 144  * Calls the @complete_type_info function from the #GTypePluginClass of @plugin.
 145  * There should be no need to use this function outside of the GObject
 146  * type system itself.
 147  */
 148 void
 149 g_type_plugin_complete_type_info (GTypePlugin     *plugin,
 150                                   GType            g_type,
 151                                   GTypeInfo       *info,
 152                                   GTypeValueTable *value_table)
 153 {
 154   GTypePluginClass *iface;
 155
 156   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 157   g_return_if_fail (info != NULL);
 158   g_return_if_fail (value_table != NULL);
 159
 160   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 161   iface->complete_type_info (plugin,
 162                              g_type,
 163                              info,
 164                              value_table);
 165 }
 166
 167 /**
 168  * g_type_plugin_complete_interface_info:
 169  * @plugin: the #GTypePlugin
 170  * @instance_type: the #GType of an instantiable type to which the interface
 171  *  is added
 172  * @interface_type: the #GType of the interface whose info is completed
 173  * @info: the #GInterfaceInfo to fill in
 174  *
 175  * Calls the @complete_interface_info function from the
 176  * #GTypePluginClass of @plugin. There should be no need to use this
 177  * function outside of the GObject type system itself.
 178  */
 179 void
 180 g_type_plugin_complete_interface_info (GTypePlugin    *plugin,
 181                                        GType           instance_type,
 182                                        GType           interface_type,
 183                                        GInterfaceInfo *info)
 184 {
 185   GTypePluginClass *iface;
 186
 187   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 188   g_return_if_fail (info != NULL);
 189
 190   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 191   iface->complete_interface_info (plugin,
 192                                   instance_type,
 193                                   interface_type,
 194                                   info);
 195 }