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      1 /* GObject - GLib Type, Object, Parameter and Signal Library
      2  * Copyright (C) 2006 Imendio AB
      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 #undef  G_LOG_DOMAIN
     20 #define G_LOG_DOMAIN "TestSingleton"
     21 #include <glib-object.h>
     22 #include <string.h>
     23 
     24 /* --- MySingleton class --- */
     25 typedef struct {
     26   GObject parent_instance;
     27 } MySingleton;
     28 typedef struct {
     29   GObjectClass parent_class;
     30 } MySingletonClass;
     31 
     32 #define MY_TYPE_SINGLETON         (my_singleton_get_type ())
     33 #define MY_SINGLETON(o)           (G_TYPE_CHECK_INSTANCE_CAST ((o), MY_TYPE_SINGLETON, MySingleton))
     34 #define MY_IS_SINGLETON(o)        (G_TYPE_CHECK_INSTANCE_TYPE ((o), MY_TYPE_SINGLETON))
     35 #define MY_SINGLETON_CLASS(c)     (G_TYPE_CHECK_CLASS_CAST ((c), MY_TYPE_SINGLETON, MySingletonClass))
     36 #define MY_IS_SINGLETON_CLASS(c)  (G_TYPE_CHECK_CLASS_TYPE ((c), MY_TYPE_SINGLETON))
     37 #define MY_SINGLETON_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), MY_TYPE_SINGLETON, MySingletonClass))
     38 
     39 G_DEFINE_TYPE (MySingleton, my_singleton, G_TYPE_OBJECT);
     40 
     41 static MySingleton *the_one_and_only = NULL;
     42 
     43 /* --- methods --- */
     44 static GObject*
     45 my_singleton_constructor (GType                  type,
     46                           guint                  n_construct_properties,
     47                           GObjectConstructParam *construct_properties)
     48 {
     49   if (the_one_and_only)
     50     return g_object_ref (the_one_and_only);
     51   else
     52     return G_OBJECT_CLASS (my_singleton_parent_class)->constructor (type, n_construct_properties, construct_properties);
     53 }
     54 
     55 static void
     56 my_singleton_init (MySingleton *self)
     57 {
     58   g_assert (the_one_and_only == NULL);
     59   the_one_and_only = self;
     60 }
     61 
     62 static void
     63 my_singleton_class_init (MySingletonClass *klass)
     64 {
     65   G_OBJECT_CLASS (klass)->constructor = my_singleton_constructor;
     66 }
     67 
     68 /* --- test program --- */
     69 int
     70 main (int   argc,
     71       char *argv[])
     72 {
     73   MySingleton *singleton, *obj;
     74   g_type_init_with_debug_flags (G_TYPE_DEBUG_OBJECTS | G_TYPE_DEBUG_SIGNALS);
     75   /* create the singleton */
     76   singleton = g_object_new (MY_TYPE_SINGLETON, NULL);
     77   g_assert (singleton != NULL);
     78   /* assert _singleton_ creation */
     79   obj = g_object_new (MY_TYPE_SINGLETON, NULL);
     80   g_assert (singleton == obj);
     81   g_object_unref (obj);
     82   /* shutdown */
     83   g_object_unref (singleton);
     84   return 0;
     85 }
     86