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, write to the
  16  * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  17  * Boston, MA 02111-1307, USA.
  18  */
  19
  20 #include "config.h"
  21
  22 #include "gtypeplugin.h"
  23
  24
  25 /**
  26  * SECTION:gtypeplugin
  27  * @short_description: An interface for dynamically loadable types
  28  * @see_also: #GTypeModule and g_type_register_dynamic().
  29  * @title: GTypePlugin
  30  *
  31  * The GObject type system supports dynamic loading of types. The
  32  * #GTypePlugin interface is used to handle the lifecycle of
  33  * dynamically loaded types.  It goes as follows:
  34  *
  35  * <orderedlist>
  36  * <listitem><para>
  37  *   The type is initially introduced (usually upon loading the module
  38  *   the first time, or by your main application that knows what modules
  39  *   introduces what types), like this:
  40  *   |[
  41  *   new_type_id = g_type_register_dynamic (parent_type_id,
  42  *                                                 "TypeName",
  43  *                                                 new_type_plugin,
  44  *                                                 type_flags);
  45  *   ]|
  46  *   where <literal>new_type_plugin</literal> is an implementation of the
  47  *   #GTypePlugin interface.
  48  * </para></listitem>
  49  * <listitem><para>
  50  *    The type's implementation is referenced, e.g. through
  51  *    g_type_class_ref() or through g_type_create_instance() (this is
  52  *    being called by g_object_new()) or through one of the above done on
  53  *    a type derived from <literal>new_type_id</literal>.
  54  * </para></listitem>
  55  * <listitem><para>
  56  *    This causes the type system to load the type's implementation by calling
  57  *    g_type_plugin_use() and g_type_plugin_complete_type_info() on
  58  *    <literal>new_type_plugin</literal>.
  59  * </para></listitem>
  60  * <listitem><para>
  61  *    At some point the type's implementation isn't required anymore, e.g. after
  62  *    g_type_class_unref() or g_type_free_instance() (called when the reference
  63  *    count of an instance drops to zero).
  64  * </para></listitem>
  65  * <listitem><para>
  66  *    This causes the type system to throw away the information retrieved from
  67  *    g_type_plugin_complete_type_info() and then it calls
  68  *    g_type_plugin_unuse() on <literal>new_type_plugin</literal>.
  69  * </para></listitem>
  70  * <listitem><para>
  71  *    Things may repeat from the second step.
  72  * </para></listitem>
  73  * </orderedlist>
  74  *
  75  * So basically, you need to implement a #GTypePlugin type that
  76  * carries a use_count, once use_count goes from zero to one, you need
  77  * to load the implementation to successfully handle the upcoming
  78  * g_type_plugin_complete_type_info() call. Later, maybe after
  79  * succeeding use/unuse calls, once use_count drops to zero, you can
  80  * unload the implementation again. The type system makes sure to call
  81  * g_type_plugin_use() and g_type_plugin_complete_type_info() again
  82  * when the type is needed again.
  83  *
  84  * #GTypeModule is an implementation of #GTypePlugin that already
  85  * implements most of this except for the actual module loading and
  86  * unloading. It even handles multiple registered types per module.
  87  */
  88
  89
  90 /* --- functions --- */
  91 GType
  92 g_type_plugin_get_type (void)
  93 {
  94   static GType type_plugin_type = 0;
  95
  96   if (!type_plugin_type)
  97     {
  98       const GTypeInfo type_plugin_info = {
  99         sizeof (GTypePluginClass),
 100         NULL,           /* base_init */
 101         NULL,           /* base_finalize */
 102       };
 103
 104       type_plugin_type = g_type_register_static (G_TYPE_INTERFACE, g_intern_static_string ("GTypePlugin"), &type_plugin_info, 0);
 105     }
 106
 107   return type_plugin_type;
 108 }
 109
 110 /**
 111  * g_type_plugin_use:
 112  * @plugin: a #GTypePlugin
 113  *
 114  * Calls the @use_plugin function from the #GTypePluginClass of
 115  * @plugin.  There should be no need to use this function outside of
 116  * the GObject type system itself.
 117  */
 118 void
 119 g_type_plugin_use (GTypePlugin *plugin)
 120 {
 121   GTypePluginClass *iface;
 122
 123   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 124
 125   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 126   iface->use_plugin (plugin);
 127 }
 128
 129 /**
 130  * g_type_plugin_unuse:
 131  * @plugin: a #GTypePlugin
 132  *
 133  * Calls the @unuse_plugin function from the #GTypePluginClass of
 134  * @plugin.  There should be no need to use this function outside of
 135  * the GObject type system itself.
 136  */
 137 void
 138 g_type_plugin_unuse (GTypePlugin *plugin)
 139 {
 140   GTypePluginClass *iface;
 141
 142   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 143
 144   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 145   iface->unuse_plugin (plugin);
 146 }
 147
 148 /**
 149  * g_type_plugin_complete_type_info:
 150  * @plugin: a #GTypePlugin
 151  * @g_type: the #GType whose info is completed
 152  * @info: the #GTypeInfo struct to fill in
 153  * @value_table: the #GTypeValueTable to fill in
 154  *
 155  * Calls the @complete_type_info function from the #GTypePluginClass of @plugin.
 156  * There should be no need to use this function outside of the GObject
 157  * type system itself.
 158  */
 159 void
 160 g_type_plugin_complete_type_info (GTypePlugin     *plugin,
 161                                   GType            g_type,
 162                                   GTypeInfo       *info,
 163                                   GTypeValueTable *value_table)
 164 {
 165   GTypePluginClass *iface;
 166
 167   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 168   g_return_if_fail (info != NULL);
 169   g_return_if_fail (value_table != NULL);
 170
 171   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 172   iface->complete_type_info (plugin,
 173                              g_type,
 174                              info,
 175                              value_table);
 176 }
 177
 178 /**
 179  * g_type_plugin_complete_interface_info:
 180  * @plugin: the #GTypePlugin
 181  * @instance_type: the #GType of an instantiable type to which the interface
 182  *  is added
 183  * @interface_type: the #GType of the interface whose info is completed
 184  * @info: the #GInterfaceInfo to fill in
 185  *
 186  * Calls the @complete_interface_info function from the
 187  * #GTypePluginClass of @plugin. There should be no need to use this
 188  * function outside of the GObject type system itself.
 189  */
 190 void
 191 g_type_plugin_complete_interface_info (GTypePlugin    *plugin,
 192                                        GType           instance_type,
 193                                        GType           interface_type,
 194                                        GInterfaceInfo *info)
 195 {
 196   GTypePluginClass *iface;
 197
 198   g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
 199   g_return_if_fail (info != NULL);
 200
 201   iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
 202   iface->complete_interface_info (plugin,
 203                                   instance_type,
 204                                   interface_type,
 205                                   info);
 206 }