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N Level Control of System Resources

IP.com Disclosure Number: IPCOM000083948D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

VanFleet, JW: AUTHOR

Abstract

INTRODUCTION: All system resources are managed at at least one level of control. Two familiar levels of control are Shared and Exclusive. The operating system VM/370 uses seven levels of control: Read, Write, Write Read, Read Read, Multiple, Multiple Read, and Multiple Write.

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N Level Control of System Resources

INTRODUCTION: All system resources are managed at at least one level of control. Two familiar levels of control are Shared and Exclusive. The operating system VM/370 uses seven levels of control: Read, Write, Write Read, Read Read, Multiple, Multiple Read, and Multiple Write.

Normally, as the number of levels of control increases, the complexity of the logic required to determine whether a resource is available also increases, hence efficiency decreases. Described is a process which efficiently determines whether a system resource with n-levels of control is available; that is, the complexity of the logic remains the same regardless of the number of levels of control.

The process presented is one example of a more general scheme of using,
1) a static matrix to contain relational information between states, 2) a vector to maintain dynamic, accumulated state information, and 3) an algorithm which draws the two together. In each application, the advantage is the same: the complexity of the logic to accomplish the algorithm is constant regardless of the number of states.

INPUTS TO THE PROCESS: To determine whether a resource is available at the level requested, the process uses three inputs: - The request for the resource at a level of control. - A dynamic state vector that indicates the levels at which the resource is currently available. There is a dynamic state

vector corresponding to each resource. The dynamic state

vector contains N indicators, one for each level of control. - An N-by-N static matrix that indicates mutually exclusive levels of control. For each level of control there

corresponds one row and one column in the matrix. The

values in the row corresponding to each level are set to 0

for all levels (columns) which are mutually exclusive with

this level; they are set to 1 for all levels (columns)

which may coexist with this level (row) when the resource is

held at this level.

Appendix A is an example of forming the 5x5 matrix for the seven VM/370 levels of control.

THE ALGORITHM: The algorithm has two steps: 1) Check the requested level entry in the dynamic state vector for the resource. If the entry is "off", the resource is not available; processing ceases. If the state vector indicates the resource is available (the entry is "on"), proceed to step 2. 2) Update the resource's state vector to reflect its new status as follows. Perform "AND" operation on the resource's existing state vector and the matrix row corresponding to the level requested. The result of the AND operation is the resource's current state vector.

OUTPUT FROM THE PROCESS: The output provided from the process is:

1

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- The determination of whether the resource is available, as

requested, or not. - The resultant state vector that indicates the levels at which the resource is currently available (after the

request).

BOUNDS OF THE PROCESS: As previously stated, the output of the process is limited to: 1) The...