Characterizing Grids: Attributes, Definitions, and Formalisms

Grid systems and technologies have evolved over nearly a decade; yet, there is still no widely accepted definition for Grids. In particular, the essential attributes that distinguish Grids from other distributed computing environments have not been articulated. Most approaches to definition adopt a static view and consider only the properties and components of, or the applications supported by, Grids. The definition proposed in this paper is based on the runtime semantics of distributed systems. Rather than attempt to simply compare static characteristics of Grids and other distributed computing environments, this paper analyzes operational differences, from the viewpoint of an application executing in both environments. Our definition is expressed formally as an Abstract State Machine that facilitates the analysis of existing Grid systems or the design of new ones with rigor and precision. This new, semantical approach proposes an alternative to the currently accepted models for determining whether or not a distributed system is a Grid.     

Collaborative Group Membership

In this paper we present a novel approach to fault-tolerant group membership for use predominantly in collaborative computing environments. As an exemplar, we use the Collaborative Computing Transport Layer which offers reliable atomic multicast capabilities for use in collaborative environments such as the Collaborative Computing Frameworks (CCF). Specific design goals of the approach are the elimination of processing overhead due to heartbeats, support for partial failures and extensibility. These goals are satisfied in an approach, termed Collaborative Group Membership (CGM), which uses a quiescent weak failure detector and two election based algorithms to form consensus on the membership of a failing group. Failure detection operates through a reliable multicast primitive and as such eliminates the need for explicit keep-alive packets; thus in a failure free environment, CGM imposes no overhead.     

Complementarity effect of governance mechanisms on environmental collaboration: does it exist?

This study evaluates the effect of pre-existing relational governance mechanisms on environmental collaboration. Specifically, our study distinguishes between structural and process dimensions of relational governance mechanisms so as to facilitate a more nuanced investigation into the inherent complementarities and performance implications. Using data collected from 145 US firms and a combination of methodologies – three-stage least squares and structural equation modelling, a number of direct, complementary and mediation effects are hypothesised and tested. The three-stage least squares methodology was adopted to overcome endogeneity and simultaneity issues inherent in the hypotheses covering complementarity. Contrary to conventional wisdom, structural and process governance mechanisms were not found to act as complements for environmental collaboration. Instead, the effect of structural mechanisms was found to be completely mediated by the process mechanisms. Thus, process mechanisms of relational governance were found to be much more important in promoting advanced practices such as environmental collaboration. Our results also document the significant mediating role of environmental collaboration. Implications for future research and practice are offered.     

Heterogeneous parallel and distributed computing

Heterogeneous network-based distributed and parallel computing is gaining increasing acceptance as an alternative or complementary paradigm to multiprocessor-based parallel processing as well as to conventional supercomputing. While algorithmic and programming aspects of heterogeneous concurrent computing are similar to their parallel processing counterparts, system issues, partitioning and scheduling, and performance aspects are significantly different. In this paper, we discuss the evolution of heterogeneous concurrent computing, in the context of the parallel virtual machine (PVM) system, a widely adopted software system for network computing. In particular, we highlight the system level infrastructures that are required, aspects of parallel algorithm development that most affect performance, system capabilities and limitations, and tools and methodologies for effective computing in heterogeneous networked environments. We also present recent developments and experiences in the PVM project, and comment on ongoing and future work.     

高压加气混凝土/CFRP夹芯板的低速撞击响应

高压加气混凝土(AAC)-CFRP复合结构已证明可作为轻型结构材料用于连梁、过梁、墙或柱子。除了必须具有足够的受弯能力,AAC/CFRP复合结构也需要具有抵抗局部破坏力的性能。在使用过程中,这些结构可能会承受类似爆炸、或龙卷风、台风、暴风雪的局部撞击、冲击。为评估AAC/CFRP夹芯板结构抗低速冲击的响应能力,通过一个能量守恒模型得出的预测能量吸收值与试验结果进行对比。在相对低速下,AAC/CFRP可以承受相对低速重物的冲击,比如物体/工具落在梁上或对柱子的低速撞击。     

HARNESS: a next generation distributed virtual machine

Heterogeneous Adaptable Reconfigurable Networked SystemS (HARNESS) is an experimental metacomputing system [L. Smarr, C.E. Catlett, Communications of the ACM 35 (6) (1992) 45–52] built around the services of a highly customizable and reconfigurable Distributed Virtual Machine (DVM). The successful experience of the HARNESS design team with the Parallel Virtual Machine (PVM) project has taught us both the features which make the DVM model so valuable to parallel programmers and the limitations imposed by the PVM design. HARNESS seeks to remove some of those limitations by taking a totally different approach to creating and modifying a DVM.     

Scheduling communication in multithreaded programs: experimental results

When the critical path of a communication session between end points includes the actions of operating system kernels, there are attendant overheads. Along with other factors, such as functionality and flexibility, such overheads motivate and favor the implementation of communication protocols in user space. When implemented with threads, such protocols may hold the key to optimal communication performance and functionality. Based on implementations of reliable user‐space protocols supported by a threads framework, we focus on our experiences with internal threads' scheduling techniques and their potential impact on performance. We present scheduling strategies that enable threads to do both application‐level and communication‐related processing. With experiments performed on a Sun SPARC‐5 LAN environment, we show how different scheduling strategies yield different levels of application‐processing efficiency, communication latency and packet‐loss. This work forms part of a larger study on the implementation of multiple thread‐based protocols in a single address space, and the benefits of coupling protocols with applications. Copyright © 2005 John Wiley & Sons, Ltd.     

Developing technologies for broad-network concurrent computing

Recent developments in networking infrastructures, computer workstation capabilities, software tools, and programming languages have motivated new approaches to broad-network concurrent computing. This paper describes extensions to concurrent computing which blend new and evolving technologies to extend users' access to resources beyond their local network. The result is a concurrent programming environment which can dynamically extend over network and file system boundaries to envelope additional resources, to enable multiple-user collaborative programming, and to achieve a more optimal process mapping. Additional aspects of the derivative environment feature extended portability and support for the accessing of legacy codes and packages. This paper describes the advantages of such a design and how they have been implemented in the environment termed “IceT”.     

SCIPVM: Parallel distributed computing on SCI workstation clusters

Workstation and PC clusters interconnected by SCI (scalable coherent interface) are very promising technologies for high-performance cluster computing. Using commercial SBus to SCI interface cards and system software and drivers, a two-workstation cluster has been constructed for initial testing and evaluation. The PVM system has been adapted to operate on this cluster using both raw channel and shared-memory access to the SCI interconnect, and preliminary communications performance tests have been carried out. To achieve mutual exclusion in accessing shared-memory segments, two protocols were used. Our preliminary results indicate that communications throughput in the range of 17.7 Mbytes/s, and round-trip latencies of 80 μs using the first and 140 μs using the second protocol, can be obtained on SCI clusters. These figures are significantly better (by a factor of 2 to 4) for small and large messages than those attainable on Fast Ethernet LANs. Since these performance results are very encouraging, we expect that, in the very near future, SCI networks will be capable of delivering several tens of Mbytes/s bandwidth and a few tens of microseconds latencies, and will significantly enhance the viability of cluster computing. Copyright © 1999 John Wiley & Sons, Ltd.