Janice M Stone

US Patent:

57427852, Apr 21, 1998

Filed:

Nov 20, 1995

Appl. No.:

8/562539

Inventors:

Harold Stuart Stone - Chappaqua NY
Janice Murphy Stone - Chappaqua NY

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G06F 1516
G06F 938

US Classification:

395393

Abstract:

Using this invention, more than one variable that is shared in a multiprocessing environment can be updated atomically. Each computer processor operating in the multiprocessing environment contains more than one reservation register which, along with this novel method, are used to place reservations on each of more than one shared variable. During the execution of a program, a plurality of shared variables can be reserved, each by its respective reservation register. A reservation is placed on a shared variable by means of a special instruction. The reservation register keeps track of: the address of the shared variable that it is reserving, the value of the modified results that are to be updated in the shared variable address, whether the variable has been updated, whether the reservation is valid, and whether the processor containing the reservation register has a privilege to update the shared variable. A reservation can be invalidated if a second processor tries to read the address of the reserved shared variable. When an instruction is encountered that tries to update a shared variable, the set of reserved modified shared variables designated by that instruction that have unupdated modified results are updated atomically if and only if all the reservations in the designated set are valid.