The ComBack Method Revisited: Caching Strategies and Extension with Delayed Duplicate Detection

Abstract

Abstract. The ComBack method is a memory reduction technique for explicit state space search algorithms. It enhances hash compaction with state reconstruction to resolve hash conflicts on-the-fly thereby ensuring full coverage of the state space. In this paper we provide two means to lower the run-time penalty induced by state reconstructions: a set of strategies to implement the caching method proposed in [18], and an extension through delayed duplicate detection that allows to group reconstructions together to save redundant work.

ASAP: An Extensible Platform for State Space Analysis

“…For these reasons we believe the tool to be suitable for students, researchers, and industrial users who would like to analyze CPN models or to experiment with different verification algorithms. ASAP has replaced CPN Tools in our group to perform verification tasks and has been used to analyze an edge router discovery protocol [14] and a dynamic mobile ad-hoc network routing protocol [9]; and to experiment with state space algorithms [18,10,11]. It is also intended to be used in a future advanced state space course at Aarhus University.…”

“…As the SSE engine of ASAP is currently single-threaded we consider extending it with parallel and distributed algorithms. In particular, we are working on a parallel version of the ComBack method of which we briefly mentioned the principle in [11].…”

“…The sweepline method [15] exploits a notion of progression exhibited by many protocols to garbage collect states during the search thereby lowering peak memory requirements. The recently developed ComBack method [18,11] is especially suited to models having complex states, e.g., with many tokens in places for CPNs. It makes it possible to represent states with 16-24 bytes independently from the model, hence achieving a memory reduction close to the one provided by hash compaction without the loss of precision associated with that method.…”