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Simple State Count Maintenance for Complex State Change Processes

IP.com Disclosure Number: IPCOM000079156D
Original Publication Date: 1973-May-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Kearney, JJ: AUTHOR

Abstract

A simple technique can be used to maintain an accurate count of elements in a particular state, where the state-change process is relatively complex. By way of example, the technique is used in a STATUS service routine used in a virtual operating system to manipulate TCB (Task Control Block) nondispatchability bits, whereby the routine must maintain a count of dispatchable TCBs.

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Simple State Count Maintenance for Complex State Change Processes

A simple technique can be used to maintain an accurate count of elements in a particular state, where the state-change process is relatively complex. By way of example, the technique is used in a STATUS service routine used in a virtual operating system to manipulate TCB (Task Control Block) nondispatchability bits, whereby the routine must maintain a count of dispatchable TCBs.

The following discussion of complexities in determining the manipulation of the dispatchable count will be contrasted to the simplicity of disclosure techniques. The caller of STATUS specifies a mask of bits to be manipulated in the TCB. If, as a result of the STATUS process any of these bits are on, the TCB is (still) nondispatchable. The manipulation typically consists of 'OR' and 'AND' processing. The TCB may or may not change state depending on: 1) The original TCB state;

2) The mask bits specified (e.g., may not turn off all which

are on);

3) Mask may be 0;

4) RB wait count value;

5) Whether set or reset requested.

The technique used in STATUS is to ignore all the above complexities and do the following. A subroutine is called before and after the TCB bit manipulation. The subroutine is passed a delta of -1 on the "before" call and +1 on the "after" call. The flow o~ the subroutine is illustrated in the drawing. It can be seen that this technique can be applied to any similar problem, where a count of elements in a par...