1 /* GObject - GLib Type, Object, Parameter and Signal Library
2 * Copyright (C) 2000 Red Hat, Inc.
3 *
4 * SPDX-License-Identifier: LGPL-2.1-or-later
5 *
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General
17 * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
18 */
19
20 #include "config.h"
21
22 #include "gtypeplugin.h"
23
24
25 /**
26 * GTypePlugin:
27 *
28 * An interface that handles the lifecycle of dynamically loaded types.
29 *
30 * The GObject type system supports dynamic loading of types.
31 * 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 * ```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 * [func@GObject.TypeClass.ref] or through [func@GObject.type_create_instance]
47 * (this is being called by [ctor@GObject.Object.new]) or through one of the above
48 * done on a type derived from `new_type_id`.
49 *
50 * 3. This causes the type system to load the type's implementation by calling
51 * [method@GObject.TypePlugin.use] and [method@GObject.TypePlugin.complete_type_info]
52 * on `new_type_plugin`.
53 *
54 * 4. At some point the type's implementation isn't required anymore, e.g. after
55 * [method@GObject.TypeClass.unref] or [func@GObject.type_free_instance]
56 * (called 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 [method@GObject.TypePlugin.complete_type_info] and then it calls
60 * [method@GObject.TypePlugin.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 * [method@GObject.TypePlugin.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 * [method@GObject.TypePlugin.use] and [method@GObject.TypePlugin.complete_type_info]
71 * again when the type is needed again.
72 *
73 * [class@GObject.TypeModule] is an implementation of `GTypePlugin` that
74 * already 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 0, /* class_init */
92 NULL, /* class_destroy */
93 NULL, /* class_data */
94 0, /* instance_size */
95 0, /* n_preallocs */
96 NULL, /* instance_init */
97 NULL, /* value_table */
98 };
99
100 type_plugin_type = g_type_register_static (G_TYPE_INTERFACE, g_intern_static_string ("GTypePlugin"), &type_plugin_info, 0);
101 }
102
103 return type_plugin_type;
104 }
105
106 /**
107 * g_type_plugin_use:
108 * @plugin: a #GTypePlugin
109 *
110 * Calls the @use_plugin function from the #GTypePluginClass of
111 * @plugin. There should be no need to use this function outside of
112 * the GObject type system itself.
113 */
114 void
115 g_type_plugin_use (GTypePlugin *plugin)
116 {
117 GTypePluginClass *iface;
118
119 g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
120
121 iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
122 iface->use_plugin (plugin);
123 }
124
125 /**
126 * g_type_plugin_unuse:
127 * @plugin: a #GTypePlugin
128 *
129 * Calls the @unuse_plugin function from the #GTypePluginClass of
130 * @plugin. There should be no need to use this function outside of
131 * the GObject type system itself.
132 */
133 void
134 g_type_plugin_unuse (GTypePlugin *plugin)
135 {
136 GTypePluginClass *iface;
137
138 g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
139
140 iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
141 iface->unuse_plugin (plugin);
142 }
143
144 /**
145 * g_type_plugin_complete_type_info:
146 * @plugin: a #GTypePlugin
147 * @g_type: the #GType whose info is completed
148 * @info: the #GTypeInfo struct to fill in
149 * @value_table: the #GTypeValueTable to fill in
150 *
151 * Calls the @complete_type_info function from the #GTypePluginClass of @plugin.
152 * There should be no need to use this function outside of the GObject
153 * type system itself.
154 */
155 void
156 g_type_plugin_complete_type_info (GTypePlugin *plugin,
157 GType g_type,
158 GTypeInfo *info,
159 GTypeValueTable *value_table)
160 {
161 GTypePluginClass *iface;
162
163 g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
164 g_return_if_fail (info != NULL);
165 g_return_if_fail (value_table != NULL);
166
167 iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
168 iface->complete_type_info (plugin,
169 g_type,
170 info,
171 value_table);
172 }
173
174 /**
175 * g_type_plugin_complete_interface_info:
176 * @plugin: the #GTypePlugin
177 * @instance_type: the #GType of an instantiatable type to which the interface
178 * is added
179 * @interface_type: the #GType of the interface whose info is completed
180 * @info: the #GInterfaceInfo to fill in
181 *
182 * Calls the @complete_interface_info function from the
183 * #GTypePluginClass of @plugin. There should be no need to use this
184 * function outside of the GObject type system itself.
185 */
186 void
187 g_type_plugin_complete_interface_info (GTypePlugin *plugin,
188 GType instance_type,
189 GType interface_type,
190 GInterfaceInfo *info)
191 {
192 GTypePluginClass *iface;
193
194 g_return_if_fail (G_IS_TYPE_PLUGIN (plugin));
195 g_return_if_fail (info != NULL);
196
197 iface = G_TYPE_PLUGIN_GET_CLASS (plugin);
198 iface->complete_interface_info (plugin,
199 instance_type,
200 interface_type,
201 info);
202 }