Creates a #GTask and then immediately calls g_task_return_error()
on it. Use this in the wrapper function of an asynchronous method
when you want to avoid even calling the virtual method. You can
then use g_async_result_is_tagged() in the finish method wrapper to
check if the result there is tagged as having been created by the
wrapper method, and deal with it appropriately if so.
Creates a #GTask and then immediately calls g_task_return_error() on it. Use this in the wrapper function of an asynchronous method when you want to avoid even calling the virtual method. You can then use g_async_result_is_tagged() in the finish method wrapper to check if the result there is tagged as having been created by the wrapper method, and deal with it appropriately if so.
See also g_task_report_new_error().