5639011
A Characterization of Lazy and Eager Semantic Solutions to the Linda Predicates Ambiguity Problem
The problems associated with Linda predicate operations inp() and rdp() are well known but not always well understood. One problem, from a purely academic standpoint, is that of semantic ambiguity in the case of failure. Despite this problem, commercial tuple space implementations all provide some version of the Linda predicate operations, and thus, problems concerning safety and liveness arise. Solutions to address these problems range from proposing extensions to an existing model of computation (CSP) to proposing alternative definitions for the Linda predicate operations themselves. While these solutions may at first appear unrelated, it is possible to relate these two disparate approaches in the context of lazy and eager semantics. The benefits of this characterization include a clearer understanding of the Linda predicates ambiguity problem, two respective solutions to this problem, and the importance of considering both lazy and eager semantic perspectives as techniques for problem solving in parallel and distributed systems.
6340669
Phylospaces: reconstructing evolutionary trees in tuple space
Phylospaces is a novel framework for reconstructing evolutionary trees in tuple space, a distributed shared memory that permits processes to communicate and coordinate with each other. Our choice of tuple space as a concurrency model is somewhat unusual, given the prominence and success of pure message passing models, such as MPI. We use phylospaces to devise cooperative Rec-I-DCM3, a population-based strategy for navigating tree space. Cooperative Rec-I-DCM3 is based on Rec-I-DCM3, the fastest sequential algorithm under maximum parsimony. We compare the performance of the algorithms on two datasets consisting of 2,000 and 7,769 taxa, respectively. Our results demonstrate that cooperative Rec-I-DCM3 outperforms its sequential counterpart by at least an order of magnitude
6308382
Cooperative Rec-I-DCM3: A Population-Based Approach for Reconstructing Phylogenies
In this paper, we study the use of cooperation as a technique for designing faster algorithms for reconstructing phylogenetic trees. Our focus is on the use of cooperation to reconstruct trees based on maximum parsimony. Our baseline algorithm is Rec-I-DCM3, the best-performing MP algorithm known-to-date. Our results demonstrate that cooperation does improve the performance of the baseline algorithm by at least an order of magnitude in terms of running time. The use of cooperation also established a new best known score on one of our datasets.
7755497
Teaching Java Concurrency to CS vs IT Students: A Matter of Emphasis
A number of colleges and universities have recently added new degree programs in Information Technology (IT), or added IT components to existing Computer Science (CS) programs. Java language and technology are almost inescapable elements of both CS and IT programs. One of Java's more advanced features, languagelevel support for concurrency in the form of explicit multithreading, is important to both CS and IT students, but for different reasons. Teaching Java concurrency to CS and IT students, therefore, presents different challenges and requires emphasizing the topic in different ways. We discuss these issues, and present our experiences from CS and IT classes taught recently, in which Java concurrency was a topic.
28781124
From Sequential Processes to Grid Computation
We introduce an extended model for view-centric reasoning, EVCR, that provides more comprehensive and flexible abstractions for representing actual concurrency. The theory of Communicating Sequential Processes (CSP) provides an interleaved semantics for reasoning about concurrency through a sequentialized trace of events recorded by an idealized observer. The theory of View-Centric Reasoning (VCR) extended CSP with notions of parallel events and views, and lazy observation, to represent the true concurrency of simultaneous events and multiple, possibly imperfect observers. But VCR could be more general still, since its events, like those of CSP, are instantaneous. This restriction precludes the possibility of observing events that partially overlap in time. EVCR permits partially overlapping events to be observed and recorded by a lazy observer. The result is a more general model of concurrency; one that is more appropriate for reasoning about network functioning and, in particular, grid computation.
7589048
Security considerations when designing a distributed file system using object storage devices
We present the design goals that led us to developing a distributed object-based secure file system, Brave. Brave uses mutually authenticated object storage devices, SCARED, to store file system data. Rather than require a new authentication infrastructure. we show how we use a simple authentication protocol that is bridged into existing security infrastructures, even if there is more than one authentication protocol or domain present. We position our work in the context of some of the current work going on in distributed secure file systems and present our implementation of our file system. We also present some security weaknesses that are shared with other distributed file systems that may not be apparent when designing these systems.
52872904
Simulative analysis of dynamic scheduling heuristics for reconfigurable computing of parallel applications
The demand for processing power has been ever increasing with the growth of high-performance computing (HPC) applications and so have the constraints restricting the solutions to such requirements. High-performance distributed and parallel computing and custom-built, hardware-based computing have attempted to address this problem with some success but at a substantial cost. Recently, systems augmented with Field-Programmable Gate Arrays (FPGAs) offering a fusion of traditional parallel and distributed machines with customizable and dynamically reconfigurable hardware have emerged as a cost-effective alternative to traditional systems. However, providing a robust runtime environment for such systems to which HPC users have become accustomed has been fraught with numerous challenges. Dynamic scheduling of large-scale HPC applications in such parallel reconfigurable computing (RC) environments is one such challenge and has not been sufficiently studied to our knowledge. In this paper, we simulatively analyze the performance of several common HPC scheduling heuristics that can be used by an automated job management service to schedule application tasks on a parallel RC system. We also present a performance prediction model which the scheduling heuristics employ to schedule several common HPC applications on a collection of typical FPGA processing platforms.
10633849
Assessing differential usage of usenet social accounting meta-data
We describe a usage study of NetscanTech, a system that generates and publishes daily a range of social metrics across three dimensions: newsgroup, author, and thread, for a set of approximately 15,000 technical newsgroups in Usenet. We bring together three interlinked datasets: survey data, usage log data and social accounting data from Usenet participation, to triangulate the relationship between various user roles and differential usage of social metrics in NetscanTech. We found our most frequent users focused on information related to individual authors far more than any other information provided. In contrast, users that visited less frequently focused more on information related to newsgroups and viewing newsgroup metrics. Our results suggest features that designers and developers of online communities may wish to include in their interfaces to support the cultivation of different community roles.
45488813
Parallel application performance on shared high performance reconfigurable computing resources
The use of a network of shared, heterogeneous workstations each harboring a reconfigurable computing (RC) system offers high performance users an inexpensive platform for a wide range of computationally demanding problems. However, effectively using the full potential of these systems can be challenging without the knowledge of the system's performance characteristics. While some performance models exist for shared, heterogeneous workstations, none thus far account for the addition of RC systems. Our analytic performance model includes the effects of the reconfigurable device, application load imbalance, background user load, basic message passing communication, and processor heterogeneity. The methodology proves to be accurate in characterizing these effects for applications running on shared, homogeneous, and heterogeneous HPRC resources. The model error in all cases was found to be less than 5% for application runtimes greater than 30s, and less than 15% for runtimes less than 30s.
835724
Database Support for Exploring Criminal Networks
An established method of comprehending the data gathered thus far in a criminal investigation is to incrementally visualize it as a network, such as in the diagram displayed below which is referred to as a link chart, to ascertain if, and how, objects of interest are connected.