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Handling IPDS Printer Nacks without Cross-Subcomponent Recursion

IP.com Disclosure Number: IPCOM000106368D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Condon, JB: AUTHOR [+4]

Abstract

An IPDS Printer Negative Acknowledgement is first detected by the Device Manager subcomponent of a PSF system. This subcomponent can be called to do printer I/O from many different subcomponents, so in most PSF implementations the Device Manager has called the Error Manager to handle the NACK. The problem is that this call from Device Manager to Error Manager introduces the possibility of complex cross-subcomponent recursive loops in the code, since the error recovery itself may require further calls back into Device Manager (to do printer I/O), which in turn can result in more printer NACKs! Such recursion is detectable and manageable, but adds significant complexity to the code and to some problem diagnosis.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Handling IPDS Printer Nacks without Cross-Subcomponent Recursion

      An IPDS Printer Negative Acknowledgement is first detected by
the Device Manager subcomponent of a PSF system.  This subcomponent
can be called to do printer I/O from many different subcomponents, so
in most PSF implementations the Device Manager has called the Error
Manager to handle the NACK.  The problem is that this call from
Device Manager to Error Manager introduces the possibility of complex
cross-subcomponent recursive loops in the code, since the error
recovery itself may require further calls back into Device Manager
(to do printer I/O), which in turn can result in more printer NACKs!
Such recursion is detectable and manageable, but adds significant
complexity to the code and to some problem diagnosis.

      A method is identified to organize the Printer Manager section
of a PSF implementation without cross-subcomponent recursion.  A
shell layer is added to the Printer Manager component to avoid the
need for recursion.

      Instead of allowing multiple subcomponents to call the Device
Manager to do I/O, a shell layer, called "Invocation Interface", is
added to the Printer Manager component.  This layer funnels all
requests for I/O operations from outside of Printer Manager through a
single point, so that in the event a printer NACK is detected, Device
Manager can simply return it to its caller (Invocation Interface).
Invocation Interface then calls Error Manager to handle the NACK.  If
I/O is needed to recover from the NACK from either...