A Fully Parallel LISP2 Compactor with Preservation of the Sliding Properties

Compacting garbage collector (GC) is widely used due to its good properties of in-place collection and heap de-fragmentation. In addition, it supports fast bump-pointer allocation and provides good access locality. Most known commercial JVM or CLR implementations use compaction algorithm in certain garbage collection scenarios, such as in full heap or mature object space collections. LISP2 compactor is one of the best-known GC algorithms. As multi-core architecture prevails, several efficient parallel compactors have been proposed. Nevertheless, there is no parallel LISP2 compactor available that can preserve all the sliding properties of its sequential counterpart. That is, to compact live data in-place into a single contiguous region in one end of the heap while maintaining the original object order. In this paper, we propose a fully parallel LISP2 compactor that keeps all the sliding properties. We also prove the correctness of the design. This parallel LISP2 compactor is fully parallel because all of its four phases are parallelized and the workloads are well balanced among the collector threads. The compactor supports fall-back compaction and adjustable boundaries that help deliver the best performance. We have implemented the parallel LISP2 compactor in Apache Harmony, a product-quality open source Java SE implementation. We evaluate and discuss the design on an Intel 8-core platform with representative benchmark.