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A Linkage Mechanism for Concurrent Update

IP.com Disclosure Number: IPCOM000040971D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Vig, GW: AUTHOR [+2]

Abstract

High availability is an essential requirement in modern computer systems. It must be possible to install new software or to replace existing defective software without suspending processing. This function is also called concurrent update.

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A Linkage Mechanism for Concurrent Update

High availability is an essential requirement in modern computer systems. It must be possible to install new software or to replace existing defective software without suspending processing. This function is also called concurrent update.

Using current linkage mechanisms, which tightly link calling and called modules, it is difficult to achieve this requirement. A new linkage mechanism is defined that can support on-line updating.

This new linkage mechanism does not link the called modules and their calling modules directly. Instead, a router routine is logically inserted between them. In addition, a linkage table is used to keep linkage information for all external symbols. Each entry in the linkage table is associated with one external symbol.

At execution time, the control flow, as illustrated above, is as follows: When B is called, control is passed to the router routine. The router routine gets the address of B and other linkage information from the linkage table entry which is assigned to B. Control is passed to B.

To implement this new linkage mechanism, two address constants are required for each external reference. One of them is used for referencing the router routine. The other one is used for referencing a linkage table entry.

Since all calling modules are linked to the router routine, it is not necessary to keep track of all address constants which reference an external symbol. When an external symbol is repl...