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Control of Accessor Stalemate Contention

IP.com Disclosure Number: IPCOM000087291D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Carnes, ML: AUTHOR [+2]

Abstract

In an automatic article handling mechanism whereby an accessor is utilized to fetch and store articles, it is desirable to have at least two accessors for reliability reasons. If a failure develops in one accessor, the second accessor can provide full service and a total shutdown is not required. Both accessors must be able to operate over the entire range of the library, either of them having access to all available storage locations within the system. It is also desirable to use both accessors simultaneously wherever possible.

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Control of Accessor Stalemate Contention

In an automatic article handling mechanism whereby an accessor is utilized to fetch and store articles, it is desirable to have at least two accessors for reliability reasons. If a failure develops in one accessor, the second accessor can provide full service and a total shutdown is not required. Both accessors must be able to operate over the entire range of the library, either of them having access to all available storage locations within the system. It is also desirable to use both accessors simultaneously wherever possible.

In order to minimize contention between both accessors, a controller assigns each accessor to fetch and/or store articles. The controller can use the following technique to minimize contention between the controllers. When the controller is given a list of jobs to do, called moves, it sorts the list and allocates the moves in the list to the accessors, thus forming two lists, one for each accessor.

The moves are then assigned one at a time to the accessors. Before an accessor may be dispatched on its assigned move, the controller must consider the position of the other accessor to prevent contention between the accessors.

When it is discovered that an assigned move cannot be made due to contention, the controller considers the next move on the list and so on to the end of the list. It is possible that neither accessor may be dispatched because all the moves in their lists have contention. The contr...