g_mutex_lock (priv->queue_lock);
g_queue_foreach (priv->op_queue, (GFunc) on_cancel_all_foreach, &operations_to_cancel);
g_mutex_unlock (priv->queue_lock);
g_mutex_lock (priv->queue_lock);
g_queue_foreach (priv->op_queue, (GFunc) on_cancel_all_foreach, &operations_to_cancel);
g_mutex_unlock (priv->queue_lock);