Incremental copying garbage collection for WAM-based Prolog systems

We present an incremental copying garbage collector for the heap in WAM-based Prolog systems. We describe a heap layout in which the heap is divided in a number of equal-sized blocks. Other changes to the standard WAM allow to garbage collect these blocks independently from each other. Independent collection of heap blocks is the basis of our incremental algorithm. Compared to other copying collectors for Prolog, this collector has several advantages. First of all, it reduces pause times by only collecting one heap block at a time. Second, our algorithm has in many cases a lower memory usage than standard semi-space copying collectors. Our algorithm is based on copying without marking (contrary to the more frequently used markcopy algorithms in the context of Prolog); but while usually a copying collector needs a to space as big as the size of its from space, our collector needs a to space only the size of one heap block. Another benefit is that this algorithm also allows for a variety of garbage collection policies (including generational ones).