Browse Prior Art Database

Method to Provide a Convert Latch Function

IP.com Disclosure Number: IPCOM000036067D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 12K

Publishing Venue

IBM

Related People

Levine, FE: AUTHOR

Abstract

A method is described to provide an efficient latch conversion capability from X to S and S to X.

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This is the abbreviated version, containing approximately 69% of the total text.

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Method to Provide a Convert Latch Function

A method is described to provide an efficient latch conversion capability from X to S and S to X.

The convert latch function switches a latch owned from the currently owned request (X or S) to the other type of request. The caller must own the latch.

If the latch is also held by a different process (S latch only), the current latch is released and an error return of NOT_AVAILABLE is returned to the caller. In this case, the caller is free to issue an unconditional X-latch.

Coding note: In converting from X to S, the post bit is cleared and other S latches from other processes are allowed to run.

The purpose of providing the convert latch function is to provide an efficient technique to change a latch request from one type to another without relinquishing control of the latch. Without this capability the original latch must be released and the new latch requested. When the original latch is requested, other processes may change the original conditions, which may cause further rework.

A typical usage of a convert latch function is when a buffer is chosen for replacement, the buffer is x-latched. This x latch is required in order to read in a buffer ( from disk ) or to initialize a buffer with new data. Before returning control to the caller, if the caller requested an S-latch, the convert latch function is used.

Using the latch data area as described in *, the following design is used to implement the convert latch functio...