Borrow, copy or steal?: loans and larceny in the orthodox canonical form

  • Authors:

  • Anthony J. H. Simons

  • Affiliations:

  • Department of Computer Science, University of Sheffield, Regent Court, 211 Portobello Street, Sheffield, S1 4DP UK

  • Venue:
  • Proceedings of the 13th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications
  • Year:
  • 1998

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Abstract

Dynamic memory management in C++ is complex, especially across the boundaries of library abstract data types. C++ libraries designed in the orthodox canonical form (OCF) alleviate some of the problems by ensuring that classes which manage any kind of heap structures faithfully copy and delete these. However, in certain common circumstances, OCF heap structures are wastefully copied multiple times. General reference counting is not an option in OCF, since a shared body violates the intended value semantics; although a copy-on-write policy can be made to work with borrowed heap structures. A simpler ownership policy, based on larceny, allows low-level memory manager objects to steal heap structures from temporary variables, in properly isolated circumstances. Various strategies for regulating theft are presented, ranging from pilfer-constructors to locks on heap data. Larceny has similarities with other transfer of ownership patterns, but is more a core implementation technique designed to improve the efficiency and effectiveness of OCF-conformant libraries.