[libpeas] Make PeasEngine a proper singleton

[Garrett Regier <gregier src gnome org>]

commit 8a9a4795aedb10399cd865e66ba565bc3f7f69c6
Author: Garrett Regier <alias301 gmail com>
Date:   Sun Feb 6 03:03:48 2011 -0800

    Make PeasEngine a proper singleton
    
    Before it would assert if you used g_object_new()
    after the default instance was created.

 libpeas/peas-engine.c  |   27 +++++++++++++++++++++------
 tests/libpeas/engine.c |   21 ++++++++++++++++++++-
 2 files changed, 41 insertions(+), 7 deletions(-)
---
diff --git a/libpeas/peas-engine.c b/libpeas/peas-engine.c
index 9aecbe7..1c6257d 100644
--- a/libpeas/peas-engine.c
+++ b/libpeas/peas-engine.c
@@ -295,12 +295,6 @@ add_loader (PeasEngine       *engine,
 static void
 peas_engine_init (PeasEngine *engine)
 {
-  /* Set the default engine pointer, for peas_engine_get_default().
-   * We only allow one single instance of a PeasEngine subclass. */
-  g_assert (default_engine == NULL);
-  default_engine = engine;
-  g_object_add_weak_pointer (G_OBJECT (engine), (gpointer *) &default_engine);
-
   if (!g_module_supported ())
     {
       g_warning ("libpeas is not able to initialize the plugins engine.");
@@ -345,6 +339,26 @@ peas_engine_garbage_collect (PeasEngine *engine)
                         NULL);
 }
 
+static GObject *
+peas_engine_constructor (GType                  type,
+                         guint                  n_construct_params,
+                         GObjectConstructParam *construct_params)
+{
+  GObject *object;
+
+  if (default_engine != NULL)
+    return g_object_ref (G_OBJECT (default_engine));
+
+  object = G_OBJECT_CLASS (peas_engine_parent_class)->constructor (type,
+                                                                   n_construct_params,
+                                                                   construct_params);
+
+  default_engine = PEAS_ENGINE (object);
+  g_object_add_weak_pointer (object, (gpointer *) &default_engine);
+
+  return object;
+}
+
 static void
 peas_engine_set_property (GObject      *object,
                           guint         prop_id,
@@ -448,6 +462,7 @@ peas_engine_class_init (PeasEngineClass *klass)
   GType the_type = G_TYPE_FROM_CLASS (klass);
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
 
+  object_class->constructor = peas_engine_constructor;
   object_class->set_property = peas_engine_set_property;
   object_class->get_property = peas_engine_get_property;
   object_class->dispose = peas_engine_dispose;
diff --git a/tests/libpeas/engine.c b/tests/libpeas/engine.c
index 3cfc0e7..f53e749 100644
--- a/tests/libpeas/engine.c
+++ b/tests/libpeas/engine.c
@@ -57,9 +57,27 @@ test_runner (TestFixture   *fixture,
 }
 
 static void
-test_engine_get_default (PeasEngine *engine)
+test_engine_new (PeasEngine *engine)
 {
+  PeasEngine *new_engine;
+
+  /* Some bindings may allow creating a PeasEngine with
+   * g_object_new(). So make sure that we get the default
+   * engine and not a new engine or an assert.
+   */
+
+  new_engine = g_object_new (PEAS_TYPE_ENGINE, NULL);
+
   g_assert (engine != NULL);
+  g_assert (engine == new_engine);
+
+  /* g_object_new() will give us a new ref */
+  g_object_unref (new_engine);
+}
+
+static void
+test_engine_get_default (PeasEngine *engine)
+{
   g_assert (engine == peas_engine_get_default ());
 }
 
@@ -304,6 +322,7 @@ main (int    argc,
               (gpointer) test_engine_##ftest, \
               test_setup, test_runner, test_teardown)
 
+  TEST ("new", new);
   TEST ("get-default", get_default);
 
   TEST ("load-plugin", load_plugin);