LNCS

Concurrent accesses to shared data structures must be synchronized to avoid data races. Coarse-grained synchronization, which locks the entire data structure, is easy to implement but does not scale. Fine-grained synchronization can scale well, but can be hard to reason about. Hand-over-hand locking, in which operations are pipelined as they traverse the data structure, combines fine-grained synchronization with ease of use. However, the traditional implementation suffers from inherent overheads. This paper introduces snapshot-based synchronization (SBS), a novel hand-over-hand locking mechanism. SBS decouples the synchronization state from the data, significantly improving cache utilization. Further, it relies on guarantees provided by pipelining to minimize synchronization that requires cross-thread communication. Snapshot-based synchronization thus scales much better than traditional hand-over-hand locking, while maintaining the same ease of use

Key Management for Secure Multicast in Hybrid Satellite Networks

This paper proposes a design for key management for secure multicast in hybrid satellite networks. Communication satellites offer an efficient way to extend IP multicast services for groups in wide-area networks. In order to be commercially viable, the multicast traffic should be accessible only to paying subscribers. Access control can be achieved by data encryption. This requires secure and efficient methods to generate, distribute and update the keys. Most current key management protocols do not scale well when applied to large dynamic groups in wide-area networks. This paper attempts to solve the above problem for groups in a hybrid network that is composed of terrestrial Ethernet LANs interconnected by ATM-based satellite channels. We investigate current group key management protocols, and design a framework for secure and scalable key management for the multicast routing architecture in the satellite network. The proposed framework is presented in detail, alongwith analysis and simulation results

A Proof System and a Decision Procedure for Equality Logic

Equality Logic with uninterpreted functions is used for proving the equivalense or refinement between systems (hardware verification, compiler translation, etc). Current approaches for deciding this type of formulas use a transformation of an equality formula to the propositional one of larger size, and then any standard SAT checker can be applied. We give an approach for deciding satisfiability of equality logic formulas (E-SAT) in conjunctive normal form. Central in our approach is a single proof rule called ER. For this single rule we prove soundness and completeness. Based on this rule we propose a complete procedure for E-SAT and prove its correctness. Applying our procedure on a variation of the pigeon hole formula yields a polynomial complexity contrary to earlier approaches to E-SA

Comparing sequences with segment rearrangements

Abstract. Computational genomics involves comparing sequences based on "similarity " for detecting evolutionary and functional relation-ships. Until very recently, available portions of the human genome sequence (and that of other species) were fairly short and sparse. Mostsequencing effort was focused on genes and other short units; similarity between such sequences was measured based on character level differ-ences. However with the advent of whole genome sequencing technology there is emerging consensus that the measure of similarity between long genome sequences must capture the rearrangements of large segmentsfound in abundance in the human genome. In this paper, we abstract the general problem of computing sequence similarity in the presence of segment rearrangements. This problem isclosely related to computing the smallest grammar for a string or the block edit distance between two strings. Our problem, like these otherproblems, is NP hard. Our main result here is a simple O(1) factor approximation algorithm for this problem. In contrast, best known approxi-mations for the related problems are factor \Omega (log n) off from the optimal. Our algorithm works in linear time, and in one pass. In proving our re-sult, we relate sequence similarity measures based on different segment rearrangements, to each other, tight up to constant factors. 1 Introduction Similarity comparison between biomolecular sequences play an important rolein computational genomics due to the premise that sequence similarity usuall