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Abstract:
We address memory management aspects of WAM-based logic programming
systems that support tabled evaluation through the use of a
suspension/resumption mechanism. We describe the memory
organization and usefulness logic of such systems, and issues that
have to be resolved for effective and efficient garbage collection.
Special attention is given to early reset in the context of
suspended computations and to what is involved in the implementation
of a segment order preserving copying collector for a tabled Prolog
system. We also report our experience from building two working
heap garbage collectors (one mark & slide and one mark & copy) for the
XSB system on top of a CHAT-based tabled abstract machine: we
discuss general implementation choices for heap garbage collection
in `plain' WAM and issues that are specific to WAM with tabling.
Finally, we compare the performance of our collectors with those of
other Prolog systems and extensively analyze their characteristics.
Thus, this article documents our own implementation and serves as
guidance to anyone interested in proper memory management of
tabled systems or systems that are similar in certain aspects.