Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing最新文献

{"title":"Constant RMR solutions to reader writer synchronization","authors":"V. Bhatt, P. Jayanti","doi":"10.1145/1835698.1835803","DOIUrl":"https://doi.org/10.1145/1835698.1835803","url":null,"abstract":"We study Reader-Writer Exclusion [1], a well-known variant of the Mutual Exclusion problem [2] where processes are divided into two classes - readers and writers - and multiple readers can be in the Critical Section (CS) at the same time, although no process may be in the CS at the same time as a writer. Since readers don't conflict with each other, they should not obstruct each other. Specifically, the concurrent entering property must be satisfied: if all writers are in the Remainder section, each reader should be able to enter the CS in a bounded number of its own steps. Three versions of the Reader-Writer Exclusion problem are commonly studied - one where writers have priority over readers, another where readers have priority, and the last where neither class has priority over the other and no process may starve. To ensure high performance on Cache-Coherent (CC) and Distributed Shared Memory (DSM) multiprocessors, algorithms should be designed to generate as few remote memory references (RMRs) as possible. It would be ideal to achieve constant RMR complexity, i.e., the worst case number of RMRs that a process generates in order to enter and exit the CS once is a constant, independent of the number of processes. Constant RMR complexity algorithms have existed for Mutual Exclusion for two decades [3, 4], but none exists for Reader-Writer Exclusion. Danek and Hadzilacos' lower bound proof implies that it is impossible to achieve sublinear RMR complexity for DSM machines [5]. For CC machines, the best existing bound, also due to Danek and Hadzilacos [5], is O(log n), where n is the number of processes. In this work, we present the first constant RMR complexity algorithms for all three versions of the Reader-Writer Exclusion problem (for CC machines).","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"104 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124644646","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":"Transactional predication: high-performance concurrent sets and maps for STM","authors":"N. Bronson, J. Casper, Hassan Chafi, K. Olukotun","doi":"10.1145/1835698.1835703","DOIUrl":"https://doi.org/10.1145/1835698.1835703","url":null,"abstract":"Concurrent collection classes are widely used in multi-threaded programming, but they provide atomicity only for a fixed set of operations. Software transactional memory (STM) provides a convenient and powerful programming model for composing atomic operations, but concurrent collection algorithms that allow their operations to be composed using STM are significantly slower than their non-composable alternatives. We introduce transactional predication, a method for building transactional maps and sets on top of an underlying non-composable concurrent map. We factor the work of most collection operations into two parts: a portion that does not need atomicity or isolation, and a single transactional memory access. The result approximates semantic conflict detection using the STM's structural conflict detection mechanism. The separation also allows extra optimizations when the collection is used outside a transaction. We perform an experimental evaluation that shows that predication has better performance than existing transactional collection algorithms across a range of workloads.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116694812","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: pan and scan","authors":"Matthew P. Johnson, A. Bar-Noy","doi":"10.1145/1835698.1835729","DOIUrl":"https://doi.org/10.1145/1835698.1835729","url":null,"abstract":"We introduce the pan and scan problem, in which cameras are configured to observe multiple target locations. A camera's configuration consists of its orientation and its zoom factor or field or view (its position is given); the quality of a target's reading by a camera depends (inversely) on both the distance and field of view. After briefly discussing an easy setting in which a target accumulates measurement quality from all cameras observing it, we move on to a more challenging setting in which for each target only the best measurement of it is counted, for which we give various results. Although both variants admit continuous solutions, we observe that we may restrict our attention to solutions based on pinned cones. For a geometrically constrained setting, we give an optimal dynamic programming algorithm. For the unconstrained setting of this problem, we prove NP-hardness, present efficient centralized and distributed 2-approximation algorithms, and observe that a PTAS exists under certain assumptions. For a synchronized distributed setting, we give a 2-approximation protocol and a (2β)/(1-α)-approximation protocol (for all 0 ≤ α ≤ 1 and β ≥ 1) with the stability feature that no target's camera assignment changes more than logβ(m/α) times. We also discuss the running times of the algorithms and study the speed-ups that are possible in certain situations.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115240834","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":"Optimal gradient clock synchronization in dynamic networks","authors":"F. Kuhn, C. Lenzen, Thomas Locher, R. Oshman","doi":"10.1145/1835698.1835799","DOIUrl":"https://doi.org/10.1145/1835698.1835799","url":null,"abstract":"We study the problem of clock synchronization in highly dynamic networks, where communication links can appear or disappear at any time. The nodes in the network are equipped with hardware clocks, but the rate of the hardware clocks can vary arbitrarily within specific bounds, and the estimates that nodes can obtain about the clock values of other nodes are inherently inaccurate. Our goal in this setting is to output a logical clock at each node, such that the logical clocks of any two nodes are not too far apart, and nodes that remain close to each other in the network for a long time are better synchronized than distant nodes. This property is called gradient clock synchronization. Gradient clock synchronization has been widely studied in the static setting. We show that the bounds for the static case also apply to our highly dynamic setting: if two nodes remain at distance d from each other for sufficiently long, it is possible to synchronize their clocks to within O(d log(D/d)), where D is the diameter of the network. This is known to be optimal for static networks, and since a static network is a special case of a dynamic network, it is optimal for dynamic networks as well. Furthermore, we show that our algorithm has optimal stabilization time: when a path of length d appears between two nodes, the time required until the skew between the two nodes is reduced to O(d log(D/d)) is O(D), which we prove is optimal.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"21 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120857242","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: the accuracy of tree-based counting in dynamic networks","authors":"S. Krishnamurthy, John Ardelius, E. Aurell, M. Dam, R. Stadler, F. Wuhib","doi":"10.1145/1835698.1835770","DOIUrl":"https://doi.org/10.1145/1835698.1835770","url":null,"abstract":"We study a simple Bellman-Ford-like protocol which performs network size estimation over a tree-shaped overlay. A continuous time Markov model is constructed which allows key protocol characteristics to be estimated under churn, including the expected number of nodes at a given (perceived) distance to the root and, for each such node, the expected (perceived) size of the subnetwork rooted at that node. We validate the model by simulations, using a range of network sizes, node degrees, and churn-to-protocol rates, with convincing results.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123394347","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":"Deterministic distributed vertex coloring in polylogarithmic time","authors":"Leonid Barenboim, Michael Elkin","doi":"10.1145/1835698.1835797","DOIUrl":"https://doi.org/10.1145/1835698.1835797","url":null,"abstract":"Consider an n-vertex graph G = (V,E) of maximum degree Δ, and suppose that each vertex v ∈ V hosts a processor. The processors are allowed to communicate only with their neighbors in G. The communication is synchronous, i.e., it proceeds in discrete rounds. In the distributed vertex coloring problem the objective is to color G with Δ + 1, or slightly more than Δ + 1, colors using as few rounds of communication as possible. (The number of rounds of communication will be henceforth referred to as running time. Efficient randomized algorithms for this problem are known for more than twenty years [1, 19]. Specifically, these algorithms produce a Δ + 1)-coloring within O(log n) time, with high probability. On the other hand, the best known deterministic algorithm that requires polylogarithmic time employs O(Δ2) colors. This algorithm was devised in a seminal FOCS'87 paper by Linial [16]. Its running time is O(log* n). In the same paper Linial asked whether one can color with significantly less than Δ2 colors in deterministic polylogarithmic time. By now this question of Linial became one of the most central long-standing open questions in this area. In this paper we answer this question in the affirmative, and devise a deterministic algorithm that employs Δ1+o(1) colors, and runs in polylogarithmic time. Specifically, the running time of our algorithm is O(f(Δ) log Δ log n, for an arbitrarily slow-growing function f(Δ) = ω(1). We can also produce O(Δ1 + η)-coloring in O(log Δ log n)-time, for an arbitrarily small constant η > 0, and O(Δ)-coloring in O(Δε log n) time, for an arbitrarily small constant ε > 0. Our results are, in fact, far more general than this. In particular, for a graph of arboricity a, our algorithm produces an O(a1 + η)-coloring, for an arbitrarily small constant η > 0, in time O(log a log n).","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"71 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125898587","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":"Breaking the O(n2) bit barrier: scalable byzantine agreement with an adaptive adversary","authors":"Valerie King, Jared Saia","doi":"10.1145/1835698.1835798","DOIUrl":"https://doi.org/10.1145/1835698.1835798","url":null,"abstract":"We describe an algorithm for Byzantine agreement that is scalable in the sense that each processor sends only Õ(√n) bits, where n is the total number of processors. Our algorithm succeeds with high probability against an adaptive adversary, which can take over processors at any time during the protocol, up to the point of taking over arbitrarily close to a 1/3 fraction. We assume synchronous communication but a rushing adversary. Moreover, our algorithm works in the presence of flooding: processors controlled by the adversary can send out any number of messages. We assume the existence of private channels between all pairs of processors but make no other cryptographic assumptions. Finally, our algorithm has latency that is polylogarithmic in n. To the best of our knowledge, ours is the first algorithm to solve Byzantine agreement against an adaptive adversary, while requiring o(n2) total bits of communication.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"17 2-3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116684391","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":"Locating a target with an agent guided by unreliable local advice: how to beat the random walk when you have a clock?","authors":"N. Hanusse, D. Ilcinkas, A. Kosowski, N. Nisse","doi":"10.1145/1835698.1835781","DOIUrl":"https://doi.org/10.1145/1835698.1835781","url":null,"abstract":"We study the problem of finding a destination node t by a mobile agent in an unreliable network having the structure of an unweighted graph, in a model first proposed by Hanusse et al [20, 21]. Each node of the network is able to give advice concerning the next node to visit so as to go closer to the target t. Unfortunately, exactly k of the nodes, called liars, give advice which is incorrect. It is known that for an n-node graph G of maximum degree Δ ≥ 3, reaching a target at a distance of d from the initial location may require an expected time of 2Ω(min d,k}), for any d,k = O(log n), even when G is a tree. This paper focuses on strategies which efficiently solve the search problem in scenarios in which, at each node, the agent may only choose between following the local advice, or randomly selecting an incident edge. The strategy which we put forward, called R/A, makes use of a timer (step counter) to alternate between phases of ignoring advice (R) and following advice (A) for a certain number of steps. No knowledge of parameters n, d, or k is required, and the agent need not know by which edge it entered the node of its current location. The performance of this strategy is studied for two classes of regular graphs with extremal values of expansion, namely, for rings and for random Δ-regular graphs (an important class of expanders). For the ring, R/A is shown to achieve an expected searching time of 2d+kΘ(1) for a worst-case distribution of liars, which is polynomial in both d and k. For random Δ-regular graphs, the expected searching time of the R/A strategy is O(k3 log3 n) a.a.s. The polylogarithmic factor with respect to n cannot be dropped from this bound; in fact, we show that a lower time bound of Ω(log n) steps holds for all d,k = Ω(log logn) in random Ω-regular graphs a.a.s. and applies even to strategies which make use of some knowledge of the environment. Finally, we study oblivious strategies which do not use any memory (in particular, with no timer). Such strategies are essentially a form of a random walk, possibly biased by local advice. We show that such biased random walks sometimes achieve drastically worse performance than the R/A strategy. In particular, on the ring, no biased random walk can have a searching time which is polynomial in d and k.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"92 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122686324","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":"Efficient distributed random walks with applications","authors":"Atish Das Sarma, Danupon Nanongkai, Gopal Pandurangan, P. Tetali","doi":"10.1145/1835698.1835745","DOIUrl":"https://doi.org/10.1145/1835698.1835745","url":null,"abstract":"We focus on the problem of performing random walks efficiently in a distributed network. Given bandwidth constraints, the goal is to minimize the number of rounds required to obtain a random walk sample. We first present a fast sublinear time distributed algorithm for performing random walks whose time complexity is sublinear in the length of the walk. Our algorithm performs a random walk of length l in Õ(√l D) rounds (with high probability) on an undirected network, where D is the diameter of the network. This improves over the previous best algorithm that ran in Õ(l2/3D1/3) rounds (Das Sarma et al., PODC 2009). We further extend our algorithms to efficiently perform k independent random walks in Õ(√kl D + k) rounds. We then show that there is a fundamental difficulty in improving the dependence on l any further by proving a lower bound of Ω(√l/log l + D) under a general model of distributed random walk algorithms. Our random walk algorithms are useful in speeding up distributed algorithms for a variety of applications that use random walks as a subroutine. We present two main applications. First, we give a fast distributed algorithm for computing a random spanning tree (RST) in an arbitrary (undirected) network which runs in Õ(√mD) rounds (with high probability; here m is the number of edges). Our second application is a fast decentralized algorithm for estimating mixing time and related parameters of the underlying network. Our algorithm is fully decentralized and can serve as a building block in the design of topologically-aware networks.","PeriodicalId":447863,"journal":{"name":"Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing","volume":"62 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123918663","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}