一种基于移动Agent技术的分布式死锁检测算法

死锁的处理长期以来一直是分布式系统的研究重点,已有许多成熟算法.随着网络技术的发展,越来越多的客户和资源可在网络中自由移动,这种可移动性使得传统算法面临了新的挑战.在这种新的应用背景下,本文结合移动Agent技术,提出了一种分布式系统死锁检测和解除算法：Agent Guard.该算法使用一个移动Agent,使其遵循一定的路线算法在各个站点间移动来收集资源请求和分配信息并进行分析,从而发现并解除死锁.模拟实验证明,A-gent Guard算法能取得较短的死锁持续时间,较小的伪死锁率,且网络的通信复杂度也有降低.     

分布式死锁检测算法中伪死锁率的研究和改进

死锁处理是分布式系统中的关键问题,其中处理死锁最主要的手段为死锁检测。在评价死锁检测算法性能时伪死锁率被视为一项重要指标,故降低伪死锁率对提高算法性能有着促进作用,而目前大多数算法改进对伪死锁率关注较少。本文阐述了伪死锁研究的意义,并对若干种死锁检测算法的伪死锁率进行研究和模拟实验,认为现有的死锁算法可分为两类:环内检测和环无关检测。并分别通过减少冗余消息和本地死锁解决两种改进方法来降低目前算法的伪死锁率,最终实验表明算法性能获得较大提高。     

分布式锁的Petri网建模及死锁检测

分布式锁管理DLM细化了锁模式的粒度,使得分布式系统具有更高的并发性,但死锁检测等锁的管理过程却更加复杂了,Petri网的应用能很好地解决该问题。为分布式锁建立Petri网模型,通过化简和合成建立系统的Petri网模型,借助Petri网的可达标识图实时检测出分布式系统的死锁状态,并查找死锁进程。     

并发操作系统中基于有色Petri网的死锁检测与避免

1.引言系统的并发性与资源的共享性是并发操作系统的主要特征,其目的是最大限度地提高计算机资源的利用率。死锁是并发操作系统必须解决的一个重要问题。人们试图用不同的方法来解决死锁问题。如Dijkstra提出的有名的死锁避免的“银行家算法”,Coffman等人给出的死锁检测算法。 Petri网模型作为模拟与分析并发、异步、分布式系统的一种有效工具,已被用于解决操作系统中的许多问题。如进程通讯中的生产者/消费者问题、哲学家用餐问题,资源竞     

Strong stable properties in distributed systems

Summary A stable property in a distributed system is a global property which once true, remains true forever. This paper refines this notion by formally introducing the concept ofstrong stable properties. A strong stable property has the nice property that it can be correctly evaluated on the consistent part of uncoordinated snapshots. Termination and deadlock are shown to be strong stable properties, whereas distributed garbage is not. We also show how to derive a simple generic algorithm for the detection of a strong stable property. The generic algorithm is illustrated by two examples: termination detection and deadlock detection. Incidentally the paper presents a very simple algorithm for termination detection. Andre Schiper has been a professor of Computer Science at EPFL (Federal Institute of Technology in Lausanne, Switzerland) since 1985, leading the Operating Systems laboratory. He graduated in Physics from the Federal Institute of technology in Zürich and received his Ph.D. in Computer Science from EPFL in 1980. In 1981–82 he spent one year at the University of Rennes, France. From 1983 to 1985, he was professor at the Engineering School in Yverdon, Switzerland. Between 1989 and 1991 André Schiper was head of the Department of Computer Science of EPFL, and during the academic year 1992–93 he was on sabbatical leave at Cornell University, Ithaca (NY). His research interests are in the areas of operating systems, distributed and fault-tolerant distributed systems, and parallelism. He is currently involved in the European Esprit project BROADCAST whose objective is the design and implementation of large scale distributed computing systems. Alain Sandoz graduated in Mathematics from the University of Neuchâtel, Switzerland, in 1984 and in Computer Science from the Federal Institute of Technology in Lausanne, Switzerland, in 1988. He received his Ph.D. in Computer Science from the Federal Institute of Technology in Lausanne in 1992. His dissertation was concerned with modelling causal relationships between transactions in distributed and replicated database systems. From 1992 to 1994 he was involved in research on fault-tolerant and large scale distributed computing systems. He is currently working on the development of information systems for the Swiss government.     

SNFS并行文件系统负载均衡技术的研究与实现

在大规模集群系统的并行运算环境中,I/O效率一直是影响系统整体性能的关键因素,并行文件系统技术是目前解决I/O性能瓶颈的有效途径之一。介绍当前并行文件系统的发展现状以及并行文件系统的类型,阐述SNFS并行文件系统的架构以及负载均衡DLC(分布式LAN客户端)技术的实现原理,并给出大规模集群系统环境中SNFS文件系统负载均衡技术的实现方法,最后,通过实际应用分析说明该技术在提升I/O性能上的优势。     

Deadlock resolution using hand-to-hand motion

This paper deals with an approach for resolving deadlock problems in the case of carrying loads by the Distributed Autonomous Robotic System (DARS). The deadblock condition appears in multiple robots which move and work autonomously. Therefore, we propose an algorithm to resolve the deadlock condition by cooperative hand-to-hand motion, which is a type of cooperative performance. This paper shows the effectiveness of hand-to-hand motion through numerical simulation. This work was presented, in part, at International Symposium on Artificial Life and Robotics, Oita, Japan, February 18–20, 1996     

一个分布式文件系统及多缓存数据－致性策略

本文介绍了我们设计实现的一个分布式操作系统ＨＩＴ－ＤＵＮＩＸ中分布式文件系统的实现要点，给出了维护分布式文件多缓存数据一致性的ＭＢＣ策略并讨论了ＭＢＣ策略中防止死锁的技术。     

Distributed deadlock resolution in store-and-forward networks

We present a simple distributed algorithm that resolves store-and-forward deadlocks in data communication networks. The basic idea of the algorithm is to detect cycles of nodes that may cause store-and-forward deadlocks, and to rotate packets along these cycles. The algorithm uses a fixed amount of storage in each node for its execution, and, under reasonable assumptions upon the routing and packet handling, it ensures that packets that enter the network arrive at their destinations in finite time.Part of this work was done while this author was on sabbatical leave with IBM, Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA.     

Task distribution using factoring load balancing in Master-Worker applications

Load imbalance among workers is one of the main causes of performance shortcomings in Master-Worker applications. We have observed that this problem is very similar to the one of scheduling distributed parallel loops, which has been widely in the literature. Thus, we have adapted one of the most successful algorithms, known as Factoring, to be used for Master-Worker applications. This has leads to a simple an elegant strategy that can be used to obtain an excellent automatic and dynamic load balancing strategy for the workers. Finally, we have assessed the resulting strategy through extensive experimentation and simulation.     

连接操作在SIMFS和EXT4上的性能比较

连接操作是关系数据库系统中最基本、最昂贵的操作,对数据库性能有巨大的影响。由于连接表存放在文件系统中,因此文件系统的性能对连接操作的性能有决定性的影响。不同文件系统的连接操作性能测试对数据库研究有重要意义,但目前相关测试较少。首先对比分析了新型内存文件系统SIMFS(Sustainable In-Memory File System)的数据读写路径与磁盘文件系统EXT4(Fourth Extended File System)I/O路径等方面的差异;然后设计实验测试了不同文件系统对连接操作的影响,其中对SIMFS和EXT4分别设置了不同的数据读写块大小和I/O块大小等测试指标。实验表明,连接操作在SIMFS和EXT4上的性能优化、块大小影响、性能提升瓶颈、硬件约束等方面均存在明显差异。在实验结果比较分析的基础上,给出了针对新型内存文件系统连接操作的优化建议。     

A distributed programs monitor for berkeley UNIX

Writing and debugging distributed programs can be difficult. When a program is working, it can be difficult to achieve reasonable execution performance. A major cause of these difficulties is a lack of tools for the programmer. We use a model of distributed computation and measurement to implement a program monitoring system for programs running on the Berkeley UNIX 4.2BSD operating system. The model of distributed computation describes the activities of the processes within a distributed program in terms of computation (internal events) and communication (external events). The measurement model focuses on external events and separates the detection of external events, event record selection and data analysis. The implementation of the measurement tools involved changes to the Berkeley UNIX kernel, and the addition of daemon processes to allow the monitoring activity to take place across machine boundaries. A user interface has also been implemented.     

分布式事务处理性能评价模型

介绍了在分布式数据库中对事务处理性能评价的模型，这种模型是建立在简化的限制性假设基础之上的，并选择了两个重要的性能评价指标：存取结点的平均数和每个结点存取数据项的平均数。     

一种面向分布式嵌入式计算机的性能评估模型

不同领域的嵌入式计算机的性能评估有很大的差异性,对分布式嵌入式计算机的性能评估需要考虑其自身特点。分析了分布式嵌入式计算机的一般特征,提出了一种结合软硬件的、面向分布式嵌入式计算机的性能评估模型。该评估模型从分布式嵌入式计算机的通用技术特征方面入手,提出了度量系统性能的指标和评估准则,具有指标定义明确、评价过程简便等优点。总结了几种常见的综合评价方法,为分布式嵌入式计算机的性能评估定义了完整的综合评价过程。通过实验表明了该方法的可行性。该研究对分布式计算机系统的体系结构设计、性能分析与改进具有重大的意义。     

Control limitations from distributed sensing: Theory and Extremely Large Telescope application

We investigate performance bounds for feedback control of distributed plants where the controller can be centralized (i.e. it has access to measurements from the whole plant), but sensors only measure differences between neighboring subsystem outputs. Such “distributed sensing” can be a technological necessity in applications where system size exceeds accuracy requirements by many orders of magnitude. We formulate how distributed sensing generally limits feedback performance robust to measurement noise and to model uncertainty, without assuming any controller restrictions (among others, no “distributed control” restriction). A major practical consequence is the necessity to cut down integral action on some modes. We particularize the results to spatially invariant systems and finally illustrate implications of our developments for stabilizing the segmented primary mirror of the European Extremely Large Telescope.     

Controller design and performance evaluation for deadlock avoidance in automated flexible manufacturing cells

In this paper, the design of a deadlock avoidance controller is described. The uncontrolled system is modeled using colored Petri nets. The system controller is based on a restrictive (not maximally permissive) deadlock avoidance policy to resolve deadlocks and control the real-time resource allocation decisions in the system. Performance evaluation of systems controlled by not maximally permissive algorithms is essential in determining the applicability and effectiveness of the control algorithms. The performance of the controlled system is compared with performance of optimal control policies to quantify the effects of the restrictiveness of the deadlock avoidance policy on system performance.     

一种面向分布式文件系统的文件预取模型的设计与实现

如何为上层应用和计算提供稳定高效的文件I/O性能,是分布式文件系统性能研究的热点。文中分析分布式文件系统在设计机理上的共同特征,基于此提出一种通用型的启发式文件预取模型,并选取HDFS平台进行系统实现。启发式文件预取对上层应用透明,采用在文件系统内部建立预取线程池的方法,以组成文件块的数据存储文件为预取单位,在分布式文件系统内部实现。这种设计思路具有一定的普适性,适合推广应用于多种分布式文件系统。实验结果表明,所述的启发式文件预取,能够有效提升分布式文件系统的I/O性能。     

一类Petri网—S4R的死锁预防策略

S4R网作为一种特殊的Petri网子类,与S' PR网相比可以建模更为复杂的、拥有多个并行加工进程的资源分配系统。针对S4R网提出了一种综合的死锁预防策略。利用MIP检验由S4R网建模的柔性制造系统的活性,在新的信标控制概念的基础上对需要控制的系统进行控制。再利用MIP检验受控网系统的活性,进一步控制不活的网系统。避免了对一些网不必要的控制以及一些网过于保守的控制,得到许可行为较多的控制器。