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This paper overviews some of the lower bounds on the complexity of implementing software transactional memory, and explains their underlying assumptions. It discusses how these lower bounds align with experimental results and design choices made in existing implementations to indicate that the transactional approach for concurrent programming must compromise either programming simplicity or scalability...
Continued population growth, coupled with increased per capita consumption of resources, poses a challenge to the quality of life of current and future generations. We cannot expect to meet the future needs of society simply by extending existing infrastructures. The necessary transformation can be enabled by a sustainable IT ecosystem made up of billions of service-oriented client devices and thousands...
Current opinion and debate surrounding the capabilities and use of the Cloud is particularly strident. By contrast, the academic community has long pursued completely decentralised approaches to service provision. In this paper we contrast these two extremes, and propose an architecture, Droplets, that enables a controlled trade-off between the costs and benefits of each. We also provide indications...
Synchronous distributed algorithms are easier to design and prove correct than algorithms that tolerate asynchrony. Yet, in the real world, networks experience asynchrony and other timing anomalies. In this paper, we address the question of how to efficiently transform an algorithm that relies on synchronization into an algorithm that tolerates asynchronous executions. We introduce a transformation...
Consider a distributed system with n processors, in which each processor receives some triggers from an external source. The distributed trigger counting problem is to raise an alert and report to a user when the number of triggers received by the system reaches w, where w is a user-specified input. The problem has applications in monitoring, global snapshots, synchronizers and other distributed settings...
This paper considers the problem of calculating dominating sets in networks with bounded degree. In these networks, the maximal degree of any node is bounded by Δ, which is usually significantly smaller than n, the total number of nodes in the system. Such networks arise in various settings of wireless and peer-to-peer communication. A trivial approach of choosing all nodes into the dominating set...
Peer-to-Peer networks are divided into two main classes: unstructured and structured. Overlays from the first class are better suited for exhaustive search, whereas those from the second class offer very efficient key-value lookups. In this paper we present a novel overlay, PathFinder, which combines the advantages of both classes within one single overlay for the first time. Our evaluation shows...
We present PermiSTM, a single-version STM that satisfies a practical notion of permissiveness, usually associated with keeping many versions: it never aborts read-only transactions, and it aborts other transactions only due to a conflicting transaction (which writes to a common item), thereby avoiding spurious aborts. It avoids unnecessary contention on the memory, being strictly disjoint-access parallel...
A generally agreed upon requirement for correctness of concurrent executions in Transactional Memory systems is that all transactions including the aborted ones read consistent values. Opacity is a recently proposed correctness criterion that satisfies the above requirement. Our first contribution in this paper is extending the opacity definition for closed nested transactions. Secondly, we define...
We extend state-of-the-art lock-free linked lists by building linked lists with special care for locality of traversals. These linked lists are built of sequences of entries that reside on consecutive chunks of memory. When traversing such lists, subsequent entries typically reside on the same chunk and are thus close to each other, e.g., in same cache line or on the same virtual memory page. Such...
Brandenburg and Anderson [1,2] recently introduced a phase-fair readers/writers lock [1,2], where read and write phases alternate: when the writer leaves the CS, any waiting reader will enter the CS before the next writer enters the CS; similarly, if a reader is in the CS and a writer is waiting, any new reader that now enters the Try section will not enter the CS before some writer enters the CS...
We study the relation between two classical types of distributed locking mechanisms, called token-based locking and permission-based locking, and several distributed data structures which use locking for synchronization. We have proposed, implemented and tested several lock-based distributed data structures, namely, two different types of counters called find&increment and increment&publish,...
Barrier synchronization is widely used in shared-memory parallel programs to synchronize between phases of data-parallel algorithms. With proliferation of many-core processors, barrier synchronization has been adapted for higher level language abstractions in new languages such as X10 wherein the processes participating in barrier synchronization are not known a priori, and the processes in distinct...
Distributed processing of real-world graphs is challenging due to their size and the inherent irregular structure of graph computations. We present hipg, a distributed framework that facilitates high-level programming of parallel graph algorithms by expressing them as a hierarchy of distributed computations executed independently and managed by the user. hipg programs are in general short and elegant;...
With the advent of many-core architectures efficient scheduling of parallel computations for higher productivity and performance has become very important. Distributed scheduling of parallel computations on multiple places needs to follow affinity and deliver efficient space, time and message complexity. Simultaneous consideration of these factors makes affinity driven distributed scheduling particularly...
We consider a client-server system in which unbounded, finite but unknown, number of clients request for service from the server. The system is passive as there is no further interaction between send-request and receive-response. We give an automata based model for such systems and a temporal logic to frame specifications. We show that the satisfiability and model checking problems for the logic are...
The condition of t-resilience stipulates that an n-process program is only obliged to make progress when at least n − t processes are correct. Put another way, the live sets, the collection of process sets such that progress is required if all the processes in one of these sets are correct, are all sets with at least n − t processes. We show that the ability of arbitrary collection of live...
We address the problem of designing distributed algorithms for large scale networks that are robust to Byzantine faults. We consider a message passing, full information model: the adversary is malicious, controls a constant fraction of processors, and can view all messages in a round before sending out its own messages for that round. Furthermore, each bad processor may send an unlimited number of...
Solving the consensus problem requires in one way or another that the underlying system satisfies synchrony assumptions. Considering a system of n processes where up to t < n/3 may commit Byzantine failures, this paper investigates the synchrony assumptions that are required to solve consensus. It presents a corresponding necessary and sufficient condition. Such a condition is formulated...
We propose and investigate a gossip based, social principles and behavior inspired decentralized mechanism (GoDisco) to disseminate information in online social community networks, using exclusively social links and exploiting semantic context to keep the dissemination process selective to relevant nodes. Such a designed dissemination scheme using gossiping over a egocentric social network is unique...
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