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.     

Multi Agent在分布式测控系统动态任务调度中的实现

Multi Agent实现是基于Multi Agent的分布式测控系统动态任务调度算法实现的关键技术。采用Java作为开发工具,根据Multi Agent的功能,详细论述了Multi Agent在分布式测控系统动态任务调度中的实现。基于Multi Agent的动态任务调度算法根据各主机的负载状态,在系统运行过程中利用移动Agent动态迁移任务。文中详细论述了利用Aglets系统开发和执行移动Agent,从而有效地提高了系统效率,实现了动态任务调度的目标。     

基于移动Agent的分布式测控系统任务调度研究

动态任务调度是分布式测控系统中的一项关键技术。基于移动Agent提出了一种新的分布式测控系统动态任务调度算法。算法采用IBM Aglets系统设计和执行移动Agent,利用移动Agent-Aglet在系统运行过程中动态迁移任务,从而有效地提高了系统效率,实现了负载均衡的目标。详细介绍了任务迁移的实现及Aglet通信机制。     

基于移动Agent的分布式路由算法研究

移动Agent技术能较好地适应Internet分布式的特点，将其引入网络分布式路由计算领域是对Internet路由系统的革新。本文指出了传统路由算法存在的问题，提出基于移动Agent的分布式路由算法，就路由表的初始化、通信网络中Agent的数量控制、网络链路故障后路由表的更新、后向Agent的消亡等方面进行了讨论，并进行了仿真实验和性能分析。     

一种分布式智能推荐系统的设计

引入移动Agent技术,提出了一种面向E-learning的集成群Agent与Web服务的分布式智能推荐系统模型MASWSIRS,构造了MASWSIRS的体系结构,并给出了系统的工作流程和MASWSIRS的实现算法.     

基于移动Agent的语义挖掘系统研究

语义Web是在分布式环境下构建复杂系统的一种新兴技术。在分析语义Web与移动Agent的基础上,提出了基于移动Agent的语义挖掘系统模型。该系统由三个层次构成：通信网络层、移动Agent平台以及基于语义Web的移动Agent服务,包括推理服务、查询服务、匹配服务、本体服务和语义扩展服务等。并且给出了改进的：粒群优化算法作为移动Agent路由判定算法,为下一步研究开发比较成熟的软件产品奠定了良好的基础。     

基于移动Agent的分布式数据挖掘平台的设计与实现

结合移动Agent应用开发方法,设计一个基于移动Agent的分布式计算应用模型.针对分布式数据计算现有方法,分析其不足,通过研究移动Agent体系结构及关键技术,从理论上探索将Agent技术与分布式数据挖掘相结合的可行性和技术优势,采用Agent技术解决分布式数据挖掘时所遇到的问题,全面、系统提出了解决方案.在此基础上,实现了一个Intranet环境下的基于移动Agent的分布式计算平台.     

基于XML的异构环境的Mobile Agents架构

移动Agent技术是集软件Agent技术、移动代码技术、分布式对象技术于一体的技术.移动Agent的编程语言限制了Agent平台的执行环境.然而由于java虚拟机的出现,Java的程序可以不需重新编译,就进行迁移.但是java的移动代理也需要架设平台上有java虚拟机的环境.为了实现一个真正的异构环境的系统,使用基于XML的移动Agent架构,即使用基于XML的移动Agent代码、使用UDDI技术来为Agent注册和查询、Web Services技术来进行通信.它更容易在异构的系统环境中相互通信和操作并更容易实现和在各种环境中得到运用.     

CORBA安全服务在移动Agent系统中的应用

详细阐述了CORBA安全服务如何应用到Agent系统中,给出了移动Agent系统的安全体系结构,解决了分布式环境下移动Agent系统的安全性问题.为实现移动Agent系统之间的安全通信提供了有力的支持.     

基于移动Agent的新型分布式入侵检测系统

通过阐述入侵检测系统的基本概念和移动Agent的优点,并将移动Agent技术与分布式技术相结合,提出了一种基于移动Agent的新型分布式入侵检测系统DIDSBMA,它具有传统入侵检测技术无法比拟的优势,极大地提高了系统的稳定性、可测量性和容错性,真正实现了分布式入侵检测。     

基于时戳的分布式数据库系统中的死锁预防策略

本文讨论了分布式数据库系统中基于时戳的死锁预防策略，分析了预防死锁问题的两种可行的动态优先级方案——等待一死亡方案和伤害一等待方案，提出了使用时戳的动态优先级死锁预防策略在解决分布式数据库系统并发控制的可行性和有效性，保证了产生死锁问题的条件不能发生，从而有效的预防了死锁，并给出了相应的实例。     

On Characterization and Correctness of Distributed Deadlock Detection

Distributed deadlock detection requires identifying the presence of certain properties in the global state of distributed systems. Distributed deadlock detection is complicated due to the lack of both global memory and a common physical clock, and due to unpredictable message delays. We characterize the formation and detection of distributed deadlocks in terms of the contents of local memory of distributed nodes/sites. We describe how the interaction between deadlock detection and deadlock resolution can lead to the detection of false deadlocks that are impossible to avoid due to inherent system limitations. We define shadow, phantom, and pseudo deadlocks in the proposed framework. We give examples of existing incorrect deadlock detection algorithms to illustrate how they violate the developed requirements for distributed deadlock detection. The characterization provides an insight into the properties of distributed deadlocks, expresses inherent limitations of distributed deadlock detection, and yields new correctness criteria for distributed deadlock detection algorithms.     

Invariant-based verification of a distributed deadlock detectionalgorithm

It is argued that most previous proposals for distributed deadlock detection are incorrect because they have used informal/intuitive arguments to prove the correctness of their algorithms. Informal and intuitive arguments are prone to errors because of the highly complex nature of distributed deadlock detection/resolution algorithms. The priority-based probe algorithm for distributed deadlock detection and resolution of A.L. Choudhary et al. (1989) is corrected, and it is formally proven that the modified algorithm is correct (i.e., that it does detect all deadlocks and does not report phantom deadlocks). The proof technique is novel in that the authors first abstract the properties of the deadlock detection and resolution algorithm by invariants, and then show that the invariants imply the desired correctness of the algorithm     

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。     

Detecting and resolving deadlocks in mobile agent systems

Mobile agents environment is a new application paradigm with unique features such as mobility and autonomy. Traditional deadlock detection algorithms in distributed computing systems do not work well in mobile agent systems due to the unique feature property of the mobile agent. Existing deadlock detection and resolution algorithms in mobile agent systems have limitations such as performance inefficiency and duplicate detection/resolution when multiple mobile agents simultaneously detect/resolve the same deadlock. To address these problems, we propose an improved deadlock detection and resolution algorithm that adopts priority-based technique and lazy reaction strategy. The priority-based technique aims to ensure that there is only one instance of deadlock detection and resolution, and it also helps reduce mobile agent movement and data traffic together with the lazy reaction strategy. The liveness and safety properties of the proposed algorithm are proved in this paper. Theoretical analysis and experimental results show that the proposed algorithm provides better performance in terms of agent movement, data traffic, and execution time.     

Deadlock detection in distributed database systems: a new algorithm and a comparative performance analysis

This paper attempts a comprehensive study of deadlock detection in distributed database systems. First, the two predominant deadlock models in these systems and the four different distributed deadlock detection approaches are discussed. Afterwards, a new deadlock detection algorithm is presented. The algorithm is based on dynamically creating deadlock detection agents (DDAs), each being responsible for detecting deadlocks in one connected component of the global wait-for-graph (WFG). The DDA scheme is a “self-tuning” system: after an initial warm-up phase, dedicated DDAs will be formed for “centers of locality”, i.e., parts of the system where many conflicts occur. A dynamic shift in locality of the distributed system will be responded to by automatically creating new DDAs while the obsolete ones terminate. In this paper, we also compare the most competitive representative of each class of algorithms suitable for distributed database systems based on a simulation model, and point out their relative strengths and weaknesses. The extensive experiments we carried out indicate that our newly proposed deadlock detection algorithm outperforms the other algorithms in the vast majority of configurations and workloads and, in contrast to all other algorithms, is very robust with respect to differing load and access profiles. Received December 4, 1997 / Accepted February 2, 1999     

Implementing CS-Prolog on a communicating process architecture

The distributed implementation techniques of CS-Prolog in a multitransputer environment are presented in the paper. The first section gives an overview of CS-Prolog including the explanation of the extra built-in predicates. Section 2 describes the distributed backtracking scheme of CS-Prolog. The solution of a natural language parser problem illustrates how CS-Prolog can be used for parallel processing. Sections 4 and 5 describe the distributed implementation; the decisions and techniques used for implementing CS-Prolog on multitransputer systems. The last section contains a demonstration example of CS-Prolog used for simulating a deadlock detection algorithm for solving a problem encountered during the distributed implementation of CS-Prolog.     

Fast, centralized detection and resolution of distributed deadlocks in the generalized model

In the literature, only a few studies have been performed on the distributed deadlock detection and resolution problem in the generalized request model. Most of the studies are based on the diffusing computation technique where propagation of probes and backward propagation of replies are required to detect deadlock. The replies carry the dependency information between processes for the initiator of the algorithm to determine deadlock. Since fast detection of deadlock is critical, we take a centralized approach that removes the need of backward propagation of replies, but sends the dependency information directly to the initiator of the algorithm. This enables reduction of time cost for deadlock detection to half of that of the existing distributed algorithms. The algorithm is extended to handle concurrent executions in order to further improve deadlock detection time, whereas the current algorithms focus only on a single execution. Simulation experiments are performed to see the effectiveness of this centralized approach as compared to previous distributed algorithms. It is found that our algorithm shows better results in several performance metrics especially in deadlock latency and algorithm execution time.     

Efficient detection and resolution of OR deadlocks in distributed systems

This paper proposes a distributed algorithm for resolving deadlocks under the OR request model. The algorithm builds a distributed spanning tree by propagating probes. An encoding scheme is devised to deduce the ancestor–descendant relationship between tree nodes, so that the initiator of the algorithm collects only non-tree edge information to detect deadlock, whereas the current algorithms require all the edge information for deadlock detection. The proposed algorithm resolves all deadlocks reachable from the initiator. Its performance in terms of number of messages and execution time is better than or comparable to that of the existing algorithms. We further showed through analytic evaluation that the suggested algorithm substantially shortens deadlock detection time.