Browse Prior Art Database

Wait/Post Without Locking in a Multiprocessing System

IP.com Disclosure Number: IPCOM000078857D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Duke, AH: AUTHOR [+2]

Abstract

Generally, shared data in a multiprocessing system must be locked before being modified. The algorithms described in Figs. A and B allow a system to implement a WAIT/POST function, without requiring the shared data to be locked.

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Wait/Post Without Locking in a Multiprocessing System

Generally, shared data in a multiprocessing system must be locked before being modified. The algorithms described in Figs. A and B allow a system to implement a WAIT/POST function, without requiring the shared data to be locked.

There are three data items, a wait flag, a post flag and a dispatchable flag, which are shared between the waiting task and the posting task. The wait flag indicates the wait routine has been entered. The post flag indicates the posting task is complete. The dispatchable flag indicates the wait routine is complete and the waiting task should not be dispatched.

Locking is not required, since the algorithms have built-in defenses against invalid conditions resulting from two simultaneous accesses to the shared data. If the dispatcher is implemented in software, these algorithms are implemented as sequences of software instructions. If the dispatcher is implemented in hardware, these algorithms are implemented as two hardware instructions.

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