Implement change signals

Support receiving and properly exposing change notifications.

This required some changes to improve the thread-safety of destroying a
DConfEngine.

It is possible that a signal would be arriving (in the worker thread) at
the exact instant that a DConfEngine was being destroyed (from the
finalize of the DConfClient or DConfSettingsBackend).  This could lead
to the object being accessed after it was finalized.

We can avoid this by using weak references and by being more careful
about when the DConfEngine is freed (by taking a ref to it in the signal
handler and releasing it when done).

1 files changed, 22 insertions, 4 deletions

diff --git a/client/dconf-client.c b/client/dconf-client.c
index ffc179e..1e3efc0 100644
--- a/client/dconf-client.c
+++ b/client/dconf-client.c
@@ -47,7 +47,7 @@ dconf_client_finalize (GObject *object)
 {
   DConfClient *client = DCONF_CLIENT (object);
 
-  dconf_engine_free (client->engine);
+  dconf_engine_unref (client->engine);
   g_main_context_unref (client->context);
 
   G_OBJECT_CLASS (dconf_client_parent_class)
@@ -103,13 +103,19 @@ dconf_engine_change_notify (DConfEngine         *engine,
                             const gchar *        tag,
                             gpointer             user_data)
 {
-  DConfClient *client = user_data;
+  GWeakRef *weak_ref = user_data;
   DConfClientChange *change;
+  DConfClient *client;
+
+  client = g_weak_ref_get (weak_ref);
+
+  if (client == NULL)
+    return;
 
   g_return_if_fail (DCONF_IS_CLIENT (client));
 
   change = g_slice_new (DConfClientChange);
-  change->client = g_object_ref (client);
+  change->client = client;
   change->prefix = g_strdup (prefix);
   change->changes = g_strdupv ((gchar **) changes);
   change->tag = g_strdup (tag);
@@ -117,13 +123,25 @@ dconf_engine_change_notify (DConfEngine         *engine,
   g_main_context_invoke (client->context, dconf_client_dispatch_change_signal, change);
 }
 
+static void
+dconf_client_free_weak_ref (gpointer data)
+{
+  GWeakRef *weak_ref = data;
+
+  g_weak_ref_clear (weak_ref);
+  g_slice_free (GWeakRef, weak_ref);
+}
+
 DConfClient *
 dconf_client_new (void)
 {
   DConfClient *client;
+  GWeakRef *weak_ref;
 
   client = g_object_new (DCONF_TYPE_CLIENT, NULL);
-  client->engine = dconf_engine_new (client);
+  weak_ref = g_slice_new (GWeakRef);
+  g_weak_ref_init (weak_ref, client);
+  client->engine = dconf_engine_new (weak_ref, dconf_client_free_weak_ref);
   client->context = g_main_context_ref_thread_default ();
 
   return client;