Currently we actually start handling incoming D-Bus messages before code in ::new-connection runs which isn't exactly ideal.

To fix this I think we're going to need

 gboolean g_dbus_connection_is_frozen ();
 void     g_dbus_connection_freeze()
 void     g_dbus_connection_thaw()

and a :frozen object property (with GObject::notify support). We're also going to need this

 /* If set, the newly created GDBusConnection will be frozen */
 G_DBUS_CONNECTION_FLAGS_FROZEN

With this API, GDBusServer will simply pass G_DBUS_CONNECTION_FLAGS_FROZEN when creating the new connection (in on_run()), run the ::new-connection signal (in an idle) and then thaw the connection. Simple as pie!