01/01/1992 09:00 AM
Computer Science
Our research is concerned with compiler- independent, tag-free garbage collection for the C++ programming language. This paper presents a mark-and-sweep collector, and explains how it ameliorates shortcomings of a previous copy collector. The new collector, like the old, uses C++\'s facilities for creating abstract data types to define a *tracked reference* type, called _roots_, at the level of the application program. A programmer wishing to utilize the garbage collection service uses these roots in place of normal, raw pointers. We present a detailed study of the cost of using roots, as compared to both normal pointers and reference counted pointers, in terms of instruction counts. We examine the efficiency of a small C++ application using roots, reference counting, manual reclamation, and conservative collection. Coding the application to use garbage collection, and analyzing the resulting efficiency, helped us identify a number of memory leaks and inefficiencies in the original, manually reclaimed version. We find that for this program, garbage collection using roots is much more efficient than reference counting, though less efficient than manual reclamation. It is hard to directly compare our collector to the conservative collector because of the differing efficiencies of their respective memory allocators.
