allow_async

Determines whether the print operation may run asynchronously or not.

Some systems don't support asynchronous printing, but those that do will return gtk_print_operation_result_in_progress as the status, and emit the done signal when the operation is actually done.

The Windows port does not support asynchronous operation at all (this is unlikely to change). On other platforms, all actions except for gtk_print_operation_action_export support asynchronous operation.