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PL/1 Technique for Handling Virtual Areas

IP.com Disclosure Number: IPCOM000079066D
Original Publication Date: 1973-Apr-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Barnett, MR: AUTHOR

Abstract

Large-data structures may be handled in PL/1 using relocatable pointers (i.e. AREA and OFFSET data types). When reference is made to an area not currently in storage a swapping activity must be initiated.

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PL/1 Technique for Handling Virtual Areas

Large-data structures may be handled in PL/1 using relocatable pointers (i.e. AREA and OFFSET data types). When reference is made to an area not currently in storage a swapping activity must be initiated.

For program clarity, the initiation and control of area swapping should be clearly distinguished from the area processing functions. This is a technique that makes area swapping transparent to the application program.

An array of areas is defined to which all application program references are made. This is termed an array of virtual areas. These virtual areas are mapped onto an array of areas existing in core, using the mechanism of iSUB defining. The iSUB mapping function is evaluated on every reference to a virtual area. By implementing the mapping function as a PL/1 function reference, page swapping may be initiated as a side effect. Consider the following declarations: DCL COREPAGE (M) AREA, PAGE (N) AREA DEFINED COREPAGE (PAGING(iSUB)). M areas are held in core and a program has reference to N virtual areas. A reference to PAGE (I) causes the invocation of procedure PAGING with I passed as argument. Within PAGING a test is made to determine whether PAGE(I) is physically in core and, if so, the approximate index to COREPAGE returned. If PAGE(I) is not in core, then page swapping is initiated prior to returning an index to COREPAGE.

As long as an area is a candidate for swapping, all references must be made using rel...