In System/38, a Control Program Facility program that writes spooled output files from an output queue to an external device, such as a printer.
input/output queue element
Although spool files exist within an output queue, they are usually selected using other criteria.
Meanwhile, a dispatcher detects the request and invokes the implementation, which runs the method and puts the result on the output queue.
So it's possible that many messages are processed off the input queue before the first message is placed onto the output queue.
input/output queue backward pointer
input/output queue length
That's easy to do: just specify multiple output queues and every message in goes to each output queue.
For example, an output queue has a text description associated with it - and also contains spool files with text in them.
Since the flow is started, the message that we just put in the input queue should be processed by the flow, transformed into XML, and put in the output queue .