A Single-Trace Cycle Collection for Reference Counting Systems

Abstract

The lack of collecting cyclic garbage is generally considered the major weakness of reference counting. Reference counted systems handle this problem by incorporating either a global tracing collector or a partial tracing collector that considers only the cycle candidates. The latter has become a preferred one as it has better scalability and locality. Most of the partial tracing collectors are based on a classical tracing scheme, called trial deletion, which needs several traces over objects and thus may impose more overhead on tracing. Though lots of works have focused on reducing unnecessary candidates for tracing, few studies resort to the cycle collection procedure. This paper presents a novel cycle collection algorithm which can detect garbage cycles in a single trace over cycle candidates. The algorithm and the correctness proof are described in detail.