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Control of DOS Task Switching Displaywrite Background Print Function

IP.com Disclosure Number: IPCOM000059762D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Heath, AW: AUTHOR [+5]

Abstract

Methods are described to provide a background convert and print capability using DOS as the operating system. DOS does not provide a task switch capability. In fact, DOS itself is not re-entrant. The first method provides a SUSPEND function which will switch tasks when the conditions are appropriate. In the "pure DOS" environment, most functions are intended to be single threaded. When a DOS application is requesting data from disk, for example, the application waits until the disk access is completed. In general, DOS is not re-entrant, and no other DOS function can be performed. If an application is waiting for a keystroke, instead of actually waiting, it may poll for a keystroke and if none is available, other useful work may be performed.

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Control of DOS Task Switching Displaywrite Background Print Function

Methods are described to provide a background convert and print capability using DOS as the operating system. DOS does not provide a task switch capability. In fact, DOS itself is not re-entrant. The first method provides a SUSPEND function which will switch tasks when the conditions are appropriate. In the "pure DOS" environment, most functions are intended to be single threaded. When a DOS application is requesting data from disk, for example, the application waits until the disk access is completed. In general, DOS is not re- entrant, and no other DOS function can be performed. If an application is waiting for a keystroke, instead of actually waiting, it may poll for a keystroke and if none is available, other useful work may be performed. Since most printers have an internal buffer from which the printer may get data, other useful work may take place during printing. This is referred to as background printing. The general approach for task switching is usually performed by the operating system at well- defined breakpoints between completely independent tasks/applications or within an application upon request. In order to support background processing of conversion and printing, a "switch task" or SUSPEND command is provided in the DisplayWrite 3 System Control Program (SCP). This SUSPEND command is basically a relinquish control request, i.e., it gives the other process a chance to run. The switch will occur if the other process is available and switching is not inhibited. The algorithm for task switching is as follows: (Save work registers on stack) If (non-running task is available) AND If (task switching is not inhibited) THEN (Save remaining registers on stack) (Toggle bit indicating which task is running) (Save current task's stack pointers) (Change sta...