Dynamic revision of choice points during garbage collection in prolog [II/III]

Abstract

We describe a technique allowing efficient reconsideration of all the current choice points whenever the garbage collector is activated. It turned out that this extra work usually saves time since the garbage collector will have less structures to consider. Moreover this extra work will be deducted from future work, if the search tree is not pruned. This technique also allows recovery of space in the local stack of the wam, thus making garbage collection of this stack worthwhile. There is no additional cost in space if a trail with (address, value) pairs is used. The Dynamic revision algorithm can however be implemented with a standard trail if space the same size as the trail contents is made available at garbage collection time.