Proceedings of the ACM Symposium on Principles of Distributed Computing最新文献

{"title":"Transactional Lock Elision Meets Combining","authors":"Alex Kogan, Yossi Lev","doi":"10.1145/3087801.3087838","DOIUrl":"https://doi.org/10.1145/3087801.3087838","url":null,"abstract":"Flat combining (FC) and transactional lock elision (TLE) are two techniques that facilitate efficient multi-thread access to a sequentially implemented data structure protected by a lock. FC allows threads to delegate their operations to another (combiner) thread, and benefit from executing multiple operations by that thread under the lock through combining and elimination optimizations tailored to the specific data structure. TLE employs hardware transactional memory (HTM) that allows multiple threads to apply their operations concurrently as long as they do not conflict. This paper explores how these two radically different techniques can complement one another, and introduces the HTM-assisted Combining Framework (HCF). HCF leverages HTM to allow multiple combiners to run concurrently with each other, as well as with other, non-combiner threads. This makes HCF a good fit for data structures and workloads in which some operations may conflict with each other while others may run concurrently without conflicts. HCF achieves all that with changes to the sequential code similar to those required by TLE and FC, and in particular, without requiring the programmer to reason about concurrency.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131274258","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distributed MST and Routing in Almost Mixing Time","authors":"M. Ghaffari, F. Kuhn, Hsin-Hao Su","doi":"10.1145/3087801.3087827","DOIUrl":"https://doi.org/10.1145/3087801.3087827","url":null,"abstract":"We present a randomized distributed algorithm that computes a minimum spanning tree in τ(G) · 2O(√(log n log log n))) rounds, in any n-node graph G with mixing time τ(G). This result provides a sub-polynomial complexity for a wide range of graphs of practical interest, and goes below the celebrated Ω(D+ √n) lower bound of Das Sarma et al. [STOC'11] which holds for some worst-case general graphs. The core novelty in this result is a distributed method for permutation routing. In this problem, one is given a number of source-destination pairs, and we should deliver one packet from each source to its destination, all in parallel, in the shortest span of time possible. Our algorithm allows us to route and deliver all these packets in τ(G) · 2O(√(log n log log n)) rounds, assuming that each node v is the source or destination for at most dG(v) packets. The main technical ingredient in this routing result is a certain hierarchical embedding of good-expansion random graphs on the base graph, which we believe can be of interest well beyond this work.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129968430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Certified Multiplicative Weights Update: Verified Learning Without Regret","authors":"Alexander Bagnall, S. Merten, Gordon Stewart","doi":"10.1145/3087801.3087852","DOIUrl":"https://doi.org/10.1145/3087801.3087852","url":null,"abstract":"The Multiplicative Weights Update method (MWU) is a simple yet powerful algorithm for learning linear classifiers, for ensemble learning a la boosting, for approximately solving linear and semidefinite systems, for computing approximate solutions to multicommodity flow problems, and for online convex optimization, among other applications. In this brief announcement, we apply techniques from interactive theorem proving to define and prove correct the first formally verified implementation of MWU (specifically, we show that our MWU is no regret). Our primary application -- and one justification of the relevance of our work to the PODC community -- is to verified multi-agent systems, such as distributed multi-agent network flow and load balancing games, for which verified MWU provides a convenient method for distributed computation of approximate Coarse Correlated Equilibria.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131282997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Object Oriented Consensus","authors":"Y. Afek, J. Aspnes, Edo Cohen, Danny Vainstein","doi":"10.1145/3087801.3087867","DOIUrl":"https://doi.org/10.1145/3087801.3087867","url":null,"abstract":"We suggest a template that reveals the structure of many consensus algorithms as a generic procedure. The template builds on a new object, vacillate-adopt-commit which is an extension of the well known adopt-commit object. In addition we extend Aspnes's conciliator object to a new object that we call a reconciliator. The consensus algorithm template works in rounds of alternating vacillate-adopt-commit and reconciliator operations. The vacillate-adopt-commit object observes the processors' preferences and suggests a preference output with a measure of confidence vacillate, adopt or commit) on the preference. The reconciliator ensures termination, by providing new preferences for the processors. We show how several key consensus algorithms exactly fit our template. Here we demonstrate the decomposition of Ben-Or's randomized algorithm. The decomposition of the Phase King Byzantine and the Paxos algorithm are given in the full paper [1]. We analyze and compare our template based on vacillate-adopt-commit and reconciliator objects to previous work [3,5], suggesting a decomposition of consensus based on adopt-commit and conciliator objects. We claim that the three return values of vacillate-adopt-commit more accurately describe existing algorithms.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115959074","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"FruitChains: A Fair Blockchain","authors":"R. Pass, E. Shi","doi":"10.1145/3087801.3087809","DOIUrl":"https://doi.org/10.1145/3087801.3087809","url":null,"abstract":"Nakamoto's famous blockchain protocol enables achieving consensus in a so-called permissionless setting---anyone can join (or leave) the protocol execution, and the protocol instructions do not depend on the identities of the players. His ingenious protocol prevents \"sybil attacks\" (where an adversary spawns any number of new players) by relying on computational puzzles (a.k.a. \"moderately hard functions\") introduced by Dwork and Naor (Crypto'92). Recent work by Garay et al (EuroCrypt'15) and Pass et al (manuscript, 2016) demonstrate that this protocol provably achieves consistency and liveness assuming a) honest players control a majority of the computational power in the network, b) the puzzle-hardness is appropriately set as a function of the maximum network delay and the total computational power of the network, and c) the computational puzzle is modeled as a random oracle. Assuming honest participation, however, is a strong assumption, especially in a setting where honest players are expected to perform a lot of work (to solve the computational puzzles). In Nakamoto's Bitcoin application of the blockchain protocol, players are incentivized to solve these puzzles by receiving rewards for every \"block\" (of transactions) they contribute to the blockchain. An elegant work by Eyal and Sirer (FinancialCrypt'14), strengthening and formalizing an earlier attack discussed on the Bitcoin forum, demonstrates that a coalition controlling even a minority fraction of the computational power in the network can gain (close to) 2 times its \"fair share\" of the rewards (and transaction fees) by deviating from the protocol instructions. In contrast, in a fair protocol, one would expect that players controlling a φ fraction of the computational resources to reap a φ fraction of the rewards. We present a new blockchain protocol---the FruitChain protocol---which satisfies the same consistency and liveness properties as Nakamoto's protocol (assuming an honest majority of the computing power), and additionally is δ-approximately fair: with overwhelming probability, any honest set of players controlling a φ fraction of computational power is guaranteed to get at least a fraction (1-δ)φ of the blocks (and thus rewards) in any Ω(κ/δ) length segment of the chain (where κ is the security parameter). Consequently, if this blockchain protocol is used as the ledger underlying a cryptocurrency system, where rewards and transaction fees are evenly distributed among the miners of blocks in a length κ segment of the chain, no coalition controlling less than a majority of the computing power can gain more than a factor (1+3δ) by deviating from the protocol (i.e., honest participation is an n/2-coalition-safe 3δ-Nash equilibrium). Finally, the FruitChain protocol enables decreasing the variance of mining rewards and as such significantly lessens (or even obliterates) the need for mining pools.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"117 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128379933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Session details: Session 8","authors":"I. Calciu","doi":"10.1145/3252880","DOIUrl":"https://doi.org/10.1145/3252880","url":null,"abstract":"","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"17 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113980875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Some Sequential Algorithms are Almost Always Parallel","authors":"G. Blelloch","doi":"10.1145/3087801.3087871","DOIUrl":"https://doi.org/10.1145/3087801.3087871","url":null,"abstract":"Over the years many interesting and efficient parallel algorithms have been developed to solve a wide variety of problems, but not much attention has been paid to studying the inherent parallelism in sequential algorithms---i.e., understanding the depth of their dependence structure, and how shallow dependence structures might beused to develop efficient parallel implementations. In this talk I will describe recent work on analyzing the dependence depth of iterative sequential algorithms---ones that loop over a collection of elements. Many of these algorithms have deep dependence chains in the worst case, but shallow chains (polylog w.h.p.) if the elements are randomly ordered. Examples include many fundamental algorithms: the Knuth shuffle for random permutations, sorting by insertion into a binary search tree, greedy maximal independent set (MIS), greedy maximal matching, greedy graph-coloring, counting cycles in a permutation, incremental k-dimensional linear programming, and incremental 2d Delaunay triangulation. An advantage of the approach is that it can lead to very simple and efficient parallel algorithms. Our MIS algorithm, for example can be coded in a dozen or so lines, and is significantly faster than Luby's algorithm on modern multicore machines. Also the approach encourages snapping the view that sequential and parallel algorithms are distinct, and instead thinking of algorithms, in general, as collections of instructions with dependences among them.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121676737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Power of Choice in Priority Scheduling","authors":"Dan Alistarh, Justin Kopinsky, Jerry Li, Giorgi Nadiradze","doi":"10.1145/3087801.3087810","DOIUrl":"https://doi.org/10.1145/3087801.3087810","url":null,"abstract":"Consider the following random process: we are given n queues, into which elements of increasing labels are inserted uniformly at random. To remove an element, we pick two queues at random, and remove the element of lower label (higher priority) among the two. The cost of a removal is the rank of the label removed, among labels still present in any of the queues, that is, the distance from the optimal choice at each step. Variants of this strategy are prevalent in state-of-the-art concurrent priority queue implementations. Nonetheless, it is not known whether such implementations provide any rank guarantees, even in a sequential model. We answer this question, showing that this strategy provides surprisingly strong guarantees: Although the single-choice process, where we always insert and remove from a single randomly chosen queue, has degrading cost, going to infinity as we increase the number of steps, in the two choice process, the expected rank of a removed element is O(n) while the expected worst-case cost is O(n log n). These bounds are tight, and hold irrespective of the number of steps for which we run the process. The argument is based on a new technical connection between \"heavily loaded\" balls-into-bins processes and priority scheduling. Our analytic results inspire a new concurrent priority queue implementation, which improves upon the state of the art in terms of practical performance.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126389856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gossip in a Smartphone Peer-to-Peer Network","authors":"Calvin C. Newport","doi":"10.1145/3087801.3087813","DOIUrl":"https://doi.org/10.1145/3087801.3087813","url":null,"abstract":"In this paper, we study the fundamental problem of gossip in the mobile telephone model: a recently introduced variation of the classical telephone model modified to better describe the local peer-to-peer communication services implemented in many popular smartphone operating systems. In more detail, the mobile telephone model differs from the classical telephone model in three ways: (1) each device can participate in at most one connection per round; (2) the network topology can undergo a parameterized rate of change; and (3) devices can advertise a parameterized number of bits about their state to their neighbors in each round before connection attempts are initiated. We begin by describing and analyzing new randomized gossip algorithms in this model under the harsh assumption of a network topology that can change completely in every round. We prove a significant time complexity gap between the case where nodes can advertise 0 bits to their neighbors in each round, and the case where nodes can advertise 1 bit. For the latter assumption, we present two solutions: the first depends on a shared randomness source, while the second eliminates this assumption using a pseudorandomness generator we prove to exist with a novel generalization of a classical result from the study of two-party communication complexity. We then turn our attention to the easier case where the topology graph is stable, and describe and analyze a new gossip algorithm that provides a substantial performance improvement for many parameters. We conclude by studying a relaxed version of gossip in which it is only necessary for nodes to each learn a specified fraction of the messages in the system. We prove that our existing algorithms for dynamic network topologies and a single advertising bit solve this relaxed version up to a polynomial factor faster (in network size) for many parameters. These are the first known gossip results for the mobile telephone model, and they significantly expand our understanding of how to communicate and coordinate in this increasingly relevant setting.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"62 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124950295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Triangle Finding and Listing in CONGEST Networks","authors":"Taisuke Izumi, F. Gall","doi":"10.1145/3087801.3087811","DOIUrl":"https://doi.org/10.1145/3087801.3087811","url":null,"abstract":"Triangle-free graphs play a central role in graph theory, and triangle detection (or triangle finding) as well as triangle enumeration (triangle listing) play central roles in the field of graph algorithms. In distributed computing, algorithms with sublinear round complexity for triangle finding and listing have recently been developed in the powerful CONGEST clique model, where communication is allowed between any two nodes of the network. In this paper we present the first algorithms with sublinear complexity for triangle finding and triangle listing in the standard CONGEST model, where the communication topology is the same as the topology of the network. More precisely, we give randomized algorithms for triangle finding and listing with round complexity O(n2/3(log n)2/3) and O(n3/4log n), respectively, where n denotes the number of nodes of the network. We also show a lower bound Ω(n1/3/log n) on the round complexity of triangle listing, which also holds for the CONGEST clique model.","PeriodicalId":324970,"journal":{"name":"Proceedings of the ACM Symposium on Principles of Distributed Computing","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132650139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}