GDBusConnection: Avoid callbacks on finalized connection

Turns out that GDBusWorker will issue callbacks (in its own thread)
even after g_dbus_worker_stop() has been called. This would rarely
happen (and unreffing a connection is even rarer) so only saw this bug
occasionally when running the gdbus-connection test case in a loop.

Fix up this issue by maintaining a set of GDBusConnection objects that
are currently "alive" and do nothing in the callbacks if the passed
user_data pointer is not in this set.

Also attempted to fix up a race condition with
_g_object_wait_for_single_ref_do() and its use of GObject toggle
references - for now, just resort to busy waiting, thereby
sidestepping the toggle reference mess altogether.

Signed-off-by: David Zeuthen <davidz@redhat.com>

gio/tests/gdbus-connection.c

@@ -116,13 +116,13 @@ test_connection_life_cycle (void)
   g_assert (!g_dbus_error_is_remote_error (error));
   g_assert (c == NULL);
   g_error_free (error);
-  error = NULL;
 
   /*
    *  Check for correct behavior when a bus is present
    */
   session_bus_up ();
   /* case 1 */
+  error = NULL;
   c = g_bus_get_sync (G_BUS_TYPE_SESSION, NULL, &error);
   g_assert_no_error (error);
   g_assert (c != NULL);
@@ -131,6 +131,7 @@ test_connection_life_cycle (void)
   /*
    * Check that singleton handling work
    */
+  error = NULL;
   c2 = g_bus_get_sync (G_BUS_TYPE_SESSION, NULL, &error);
   g_assert_no_error (error);
   g_assert (c2 != NULL);
@@ -1070,12 +1071,13 @@ test_connection_basic (void)
   g_assert (exit_on_close);
   g_assert (flags == G_DBUS_CAPABILITY_FLAGS_NONE ||
             flags == G_DBUS_CAPABILITY_FLAGS_UNIX_FD_PASSING);
-
   g_object_unref (stream);
-  g_object_unref (connection);
   g_free (name);
   g_free (guid);
 
+  _g_object_wait_for_single_ref (connection);
+  g_object_unref (connection);
+
   session_bus_down ();
 }