Knowledge in shared memory systems

Summary We study the relation between knowledge and space. That is, we analyze how much shared memory space is needed in order to learn certain kinds of facts. Such results are useful tools for reasoning about shared memory systems. In addition we generalize a known impossibility result, and show that results about how knowledge can be gained and lost in message passing systems also hold for shared memory systems. Michael Merritt received a B.S. degree in Philosophy and in Computer Science from Yale College in 1978, the M.S. and Ph.D. degrees in Information and Computer Science in 1980 and 1983, respectively, from the Georgia Institute of Technology. Since 1983 he has been a member of technical staff at AT & T Bell Laboratories, and has taught as an adjunct or visiting lecturer at Stevens Institute of Technology, Massachusetts Institute of Technology, and Columbia University. In 1989 he was program chair for the ACM Symposium on Principles of Distributed Computing. His research interests include distributed and concurrent computation, both algorithms and formal methods for verifying their correctness, cryptography, and security. He is an editor for Distributed Computing and for Information and Computation, recently co-authored a book on database concurrency control algorithms, and is a member of the ACM and of Computer Professionals for Social Responsibility. Gadi Taubenfeld received the B.A., M.Sc. and Ph.D. degrees in Computer Science from the Technion (Israel Institute of Technology), in 1982, 1984 and 1988, respectively. From 1988 to 1990 he was a research scientist at Yale University. Since 1991 he has been a member of technical staff at AT & T Bell Laboratories. His primary research interests are in concurrent and distributed computing.A preliminary version of this work appeared in the Proceedings of the Tenth Annual ACM Symposium on Principles of Distributed Computing, pages 189–200, Montreal, Canada, August 1991     

Adaptive scheduling for shared window joins over data streams

Recently a few Continuous Query systems have been developed to cope with applications involving continuous data streams. At the same time, numerous algorithms are proposed for better performance. A recent work on this subject was to define scheduling strategies on shared window joins over data streams from multiple query expressions. In these strategies, a tuple with the highest priority is selected to process from multiple candidates. However, the performance of these static strategies is deeply influenced when data are bursting, because the priority is determined only by static information, such as the query windows, arriving order, etc. In this paper, we propose a novel adaptive strategy where the priority of a tuple is integrated with realtime information. A thorough experimental evaluation has demonstrated that this new strategy can outperform the existing strategies.     

Accommodating mixed sensory/modal preferences in collaborative writing systems

Writers use the abstractions of words to create meaning. But the activity of writing spans multiple concrete senses and modes. Technology-enhanced collaborative writing systems need to be sensitive to the preferred senses and modes of information in which writing teams want to work. Some preferences seem rooted in the senses (seeing vs. motor coordination); others seem based in the preferred modality of inputting or outputting information (speaking vs. writing; listening vs. reading). Still others seem based in the role of the writer on the team (author or commenter). We offer a framework for understanding some of these preferences and a prototype editor (the Prep Editor) we have been using to study them empirically.     

Accommodating change

The third of Berman and Hafner’s early nineties papers on reasoning with legal cases concerned temporal context, in particular the evolution of case law doctrine over time in response to new cases and against a changing background of social values and purposes. In this paper we consider the ways in which changes in case law doctrine can be accommodated in a recently proposed methodology for encapsulating case law theories (the ANGELIC methodology based on Abstract Dialectical Frameworks), and relate these changes the sources of change identified by Berman and Hafner.     

Design tradeoffs for process scheduling in shared memorymultiprocessor systems

A potential system software bottleneck is demonstrated in designing an efficient process scheduling method for multiprocessor systems with shared-memory communication mechanism. The process scheduling overhead is considered. The main contribution of this work is to find the design tradeoffs between monitor bottleneck due to scheduling overhead and low process utilization due to load imbalancing. Choosing an optimum number of scheduling monitors is the key to resolve the bottlenecks. Because of the excessive number of memory requests generated by the dynamic monitor selection method, the use of the fixed monitor selection method is recommended. An analytic estimation provides a lower bound in determining the optimum number of monitors. Hill-climbing simulation is then used to find the optimum number of monitors     

Time-sensitivity-aware shared cache architecture for multi-core embedded systems

The Journal of Supercomputing - In embedded systems such as automotive systems, multi-core processors are expected to improve performance and reduce manufacturing cost by integrating multiple...     

基于共享基础数据的信息系统集成方案

为解决企业信息系统集成中跨系统数据访问难的问题,提出基于共享基础数据资源的企业信息基础设施建设的理论基础、整体框架和实施方案.通过分析企业各种应用系统中所涉及的共享基础数据,构建基于共享基础数据资源平台的企业信息系统整体框架,并简单介绍按此方法实施的一个企业信息化基础设施建设的实际例子.     

The renaming problem in shared memory systems: An introduction

Exploring the power of shared memory communication objects and models, and the limits of distributed computability are among the most exciting research areas of distributed computing. In that spirit, this paper focuses on a problem that has received considerable interest since its introduction in 1987, namely the renaming problem. It was the first non-trivial problem known to be solvable in an asynchronous distributed system despite process failures. Many algorithms for renaming and variants of renaming have been proposed, and sophisticated lower bounds have been proved, that have been a source of new ideas of general interest to distributed computing. It has consequently acquired a paradigm status in distributed fault-tolerant computing.In the renaming problem, processes start with unique initial names taken from a large name space, then deciding new names such that no two processes decide the same new name and the new names are from a name space that is as small as possible.This paper presents an introduction to the renaming problem in shared memory systems, for non-expert readers. It describes both algorithms and lower bounds. Also, it discusses strong connections relating renaming and other important distributed problems such as set agreement and symmetry breaking.     

Towards a shared systems model of stakeholders in environmental conflict

Developing a shared mental model of stakeholders in conflict is a challenge in environmental conflict management. In this paper, we describe the development of a shared systems model of stakeholders in environmental conflict in the Transmission Gully project, a large‐scale transport infrastructure project in the Wellington region of New Zealand. Selected stakeholders of this project partook in generating this shared model, in the form of a causal loop diagram. This model was then analysed qualitatively to provide different insights into potential system behaviours.     

Accommodating Unique User Needs

Designing reliable, flexible user interfaces can be more of a challenge than it first appears to be. To provide a system that can be used by many and still be responsive to individual needs is an elusive goal. This column discusses the real need that exists today for a truly user-friendly interface.     

Memory reservation and shared page management for real-time systems

Memory reservations are used to provide real-time tasks with guaranteed memory access to a specified amount of physical memory. However, previous work on memory reservation primarily focused on private pages, and did not pay attention to shared pages, which are widely used in current operating systems. With previous schemes, a real-time task may experience unexpected timing delays from other tasks through shared pages that are shared by another process, even though the task has enough free pages in its own reservation. In this paper, we first describe the problems that arise when real-time tasks share pages. We then propose a shared-page management framework which enhances the temporal isolation provided by memory reservations in resource kernels that use the resource reservation approach. Our proposed solution consists of two schemes, Shared-Page Conservation (SPC) and Shared-Page Eviction Lock (SPEL), each of which prevents timing penalties caused by the seemingly arbitrary eviction of shared pages. The framework can manage shared data for inter-process communication and shared libraries, as well as pages shared by the kernel’s copy-on-write technique and file caches. We have implemented and evaluated our schemes on the Linux/RK platform, but it can also be applied to other operating systems with paged virtual memory.     

Sub-channel shared resource allocation for multi-user distributed MIMO-OFDM systems

Well-controlled resource allocation is crucial for promoting the performance of multiple input multiple output orthogonal frequency division multiplexing （MIMO-OFDM） systems. Recent studies have focused primarily on traditional centralized systems or distributed antenna systems （DASs）, and usually assumed that one sub-carrier or sub-channel is exclusively occupied by one user. To promote system performance, we propose a sub-channel shared resource allocation algorithm for multiuser distributed MIMO-OFDM systems. Each sub-channel can be shared by multiple users in the algorithm, which is different from previous algorithms. The algorithm assumes that each user communicates with only two best ports in the system. On each sub-carrier, it allocates a sub-channel in descending order, which means one sub-channel that can minimize signal to leakage plus noise ratio （SLNR） loss is deleted until the number of remaining sub-channels is equal to that of receiving antennas. If there are still sub-channels after all users are processed, these sub-channels will be allocated to users who can maximize the SLNR gain. Simulations show that compared to other algorithms, our proposed algorithm has better capacity performance and enables the system to provide service to more users under the same capacity constraints.     

A survey of recoverable distributed shared virtual memory systems

Distributed Shared Virtual Memory (DSVM) systems provide a shared memory abstraction on distributed memory architectures. Such systems ease parallel application programming because the shared-memory programming model is often more natural than the message-passing paradigm. However, the probability of failure of a DSVM increases with the number of sites. Thus, fault tolerance mechanisms must be implemented in order to allow processes to continue their execution in the event of a failure. This paper gives an overview of recoverable DSVMs (RDSVMs) that provide a checkpointing mechanism to restart parallel computations in the event of a site failure     

Reliability-aware low energy scheduling in real time systems with shared resources

Dynamic voltage scaling (DVS) is a technique which is widely used to save energy in a real time system. Recent research shows that it has a negative impact on the system reliability. In this paper, we consider the problem of the system reliability and focus on a periodic task set that the task instance shares resources. Firstly, we present a static low power scheduling algorithm for periodic tasks with shared resources called SLPSR which ignores the system reliability. Secondly, we prove that the problem of the reliability-aware low power scheduling for periodic tasks with shared resources is NP-hard and present two heuristic algorithms called SPF and LPF respectively. Finally, we present a dynamic low power scheduling algorithm for periodic tasks with shared resources called DLPSR to reclaim the dynamic slack time to save energy while preserving the system reliability. Experimental results show that the presented algorithm can reduce the energy consumption while improving the system reliability.     

Relationships between broadcast and shared memory in reliable anonymous distributed systems

We study the power of reliable anonymous distributed systems, where processes do not fail, do not have identifiers, and run identical programmes. We are interested specifically in the relative powers of systems with different communication mechanisms: anonymous broadcast, read-write registers, or read-write registers plus additional shared-memory objects. We show that a system with anonymous broadcast can simulate a system of shared-memory objects if and only if the objects satisfy a property we call idemdicence this result holds regardless of whether either system is synchronous or asynchronous. Conversely, the key to simulating anonymous broadcast in anonymous shared memory is the ability to count: broadcast can be simulated by an asynchronous shared-memory system that uses only counters, but read-write registers by themselves are not enough. We further examine the relative power of different types and sizes of bounded counters and conclude with a non-robustness result. James Aspnes is a Professor of Computer Science at Yale University. He received his Ph.D. from Carnegie-Mellon University in 1992. Faith Ellen Fich is a Professor of Computer Science at the University of Toronto. She received her Ph.D. from the University of California, Berkeley in 1982. Eric Ruppert was educated at the University of Toronto, where he completed his doctorate in 1999. He spent a year as a postdoctoral fellow at Brown University and is an Associate Professor at York University.     

线性控制系统窗口频域分析与设计

针对局部频率范围提出了窗口H∞范数的新概念,指出传统H∞范数是窗口H∞.范数的特例.利用GKYP引理证明了广义界实定理,研究了线性控制系统在窗口频域的性能分析问题.基于近似模型匹配原则和广义界实定理,将控制器设计问题转化为窗口H∞范数优化问题.仿真实例表明,窗口H∞范数适于窗口频域的线性控制系统分析和设计.     

Tight bounds for shared memory systems accessed by Byzantine processes

We provide efficient constructions and tight bounds for shared memory systems accessed by n processes, up to t of which may exhibit Byzantine failures, in a model previously explored by Malkhi et al. [21]. We show that sticky bits are universal in the Byzantine failure model for n ≥ 3t + 1, an improvement over the previous result requiring n ≥ (2t + 1)(t + 1). Our result follows from a new strong consensus construction that uses sticky bits and tolerates t Byzantine failures among n processes for any n ≥ 3t + 1, the best possible bound on n for strong consensus. We also present tight bounds on the efficiency of implementations of strong consensus objects from sticky bits and similar primitive objects. Research supported in part by a grant from the Israel Science Foundation, and by the Hermann Minkowski Minerva Center for Geometry at Tel Aviv University. This work was partially completed while at AT&T Labs and while visiting the Institute for Advanced Study, Princeton, NJ. Research supported in part by US-Israel Binational Science Foundation Grant 2002246. This work was partially completed while visiting AT&T Labs. This work was partially completed while at AT&T Labs. Research supported in part by the National Science Foundation under Grant No. CCR-0331584. A preliminary version of the results presented in this paper appeared in [23].