Software Architectures for Reducing Priority Inversion and Non-determinism in Real-time Object Request Brokers

There is increasing demand to extend Object RequestBroker (ORB) middleware to support distributed applications withstringent real-time requirements. However, conventional ORB implementations,such as CORBA ORBs, exhibit substantial priority inversion andnon-determinism, which makes them unsuitable for applicationswith deterministic real-time requirements. This paper providestwo contributions to the study and design of real-time ORB middleware.First, it illustrates empirically why conventional ORBs do notyet support real-time quality of service. Second, it evaluatesconnection and concurrency software architectures to identifystrategies that reduce priority inversion and non-determinismin real-time CORBA ORBs. The results presented in this paperdemonstrate the feasibility of using standard OO middleware likeCORBA to support certain types of real-time applications overthe Internet.     

MobiPADS: a reflective middleware for context-aware mobile computing

Traditionally, middleware technologies, such as CORBA, Java RMI, and Microsoft's DCOM, have provided a set of distributed computing services that essentially abstract the underlying network services to a monolithic "black box." In a mobile operating environment, the fundamental assumption of middleware abstracting a unified distributed service for all types of applications operating over a static network infrastructure is no longer valid. In particular, mobile applications are not able to leverage the benefits of adaptive computing to optimize its computation based on current contextual situations. In this paper, we introduce the Mobile Platform for Actively Deployable Service (MobiPADS) system. MobiPADS is designed to support context-aware processing by providing an executing platform to enable active service deployment and reconfiguration of the service composition in response to environments of varying contexts. Unlike most mobile middleware, MobiPADS supports dynamic adaptation at both the middleware and application layers to provide flexible configuration of resources to optimize the operations of mobile applications. Within the MobiPADS system, services (known as mobilets) are configured as chained service objects to provide augmented services to the underlying mobile applications so as to alleviate the adverse conditions of a wireless environment.     

CORBA实时性研究初探

ＣＯＲＢＡ是有关用于简化分布式应用与服务软件开发的对象请求中介的一个中间件标准。该文主要讨论了基于ＣＯＲＢＡ的对象请求中介的两个方面。首先,论述了常规ＣＯＲＢＡ实现中有关性能优化及服务质量上的缺陷;其次,阐述了实时应用对基于ＣＯＲＢＡ的对象请求中介的要求,并提供有关性能优化策略。     

一个实时CORBA的动态调度服务模型

在实时CORBA中引入调度服务简化了实时应用的开发,但目前实时CORBA1．0所定义的调度服务使用固定优先级调度策略只能适合于一个封闭的CORBA应用系统．本文针对这一局限性,提出了一个基于客户调度器和服务调度器相协作的动态调度服务模型对其进行扩展,使得调度服务可以适用于一个更为开放的实时CORBA系统．     

Enhancing O-O Middleware to Become Time-Aware

The general trend in middleware movestowards object-orientation. Implementation hiding, inheritance, andpolymorphism are concepts, that have turned out to be well suited for thestructuring of new complex distributed applications as well as for theintegration of legacy systems. The existence of CORBA as a vendor-independentstandard for object-oriented middleware has added another momentumto this development. Regarding real-time requirement, however,there exists an obvious trade-off. While implementation hidingisolates module implementations and eases their integration asit allows to simply match interfaces, it ignores the fact thatin the real-time domain implementation does matter. To solvethis problem, we need a system that is capable to adapt in apredictable manner to dynamic, unpredictable changes in its environment.In this paper we present our approach for an adaptive real-timesystem. It provides a run-time support system comprising run-timemonitoring and on-line, fault-tolerant scheduling as its keycomponents. It can be used to enhance emerging object-orientedde facto standards like CORBA with adequate features to integratethem as ``time-aware' components.     

面向可重构控制器实时中间件的设计与实现

可重构控制器的出现要求系统软件模块不但要满足性能和精度要求,还应具有模块化、可集成、可重用等特性.如果将实时中间件引入到控制器的设计中,由中间件管理模块间的交互,可实现控制器的可重构.建立基于RTLinux和实时CORBA的实时中间件平台,需要将CORBA引入RTLinux实时内核空间.该文给出了RTLinux实时内核中的实时CORBA和minimum CORBA实现RTCK的设计,并基于RTLinux MBuff共享内存驱动和实时FIFO设计和实现了GIOP通信协议,最后给出了RTCK与TAO的延迟抖动测试结果并做了相关的分析.     

The design of a configurable and reconfigurable middleware platform

Summary. It is now well established that middleware platforms must accommodate an increasingly diverse range of requirements arising from the needs of both applications and underlying systems. Moreover, it is clear that to achieve this accommodation, platforms must be capable of both deployment-time configurability and run-time reconfigurability. This paper describes a middleware platform that addresses these requirements. The platform is built using a well-founded lightweight component model, uses reflective techniques to facilitate (re)configuration, and employs the notion of component frameworks to manage and constrain the scope of reconfiguration operations. Importantly, the platform also aims to achieve high performance and a level of standards conformance (e.g., with CORBA and COM). We demonstrate that, despite its high degree of configurability, the platform performs on a par with standard commercial CORBA ORBs. Received: April 2001 / Accepted: September 2001     

线程库的研究与实现

本文详细论述了分布式中间件和分布式应用开发对线程库的需求,并结合实时CORBA中间件开发的实际,提出了一个具有Java风格的线程接口、统一线程优先级、能够在不同平台上运行、具有多级调度能力、满足分时和实时应用的面向对象线程库;给出了线程库中关键技术的解决方法和相关算法。     

基于SOA架构的实时通讯机制在电力行业计量自动化系统中的应用

电力行业的计量自动化系统,是以SOA架构模式的应用系统,随着应用需求复杂度的提高以及实时应用能力要求的不断提升．传统DCOM、CORBA、RMI等中间件技术逐渐显露出它的弊端。SUN公司推出的JMS技术规范是一种面向消息的中间件MOM．它能够很好的解决电力计量自动化系统的实时通讯问题。该文阐述了一种传统的后台实时架构模式＋SOA架构模式来设计电力计量自动化系统．在技术架构和应用上都能够满足现有需求。     

实时CORBA中优先级翻转的分析及解决方案

随着实时CORBA规范的推出，在实时领域内CORBA的应用需求日益增加。本文阐述了将CORBA应用于实时系统中优先级翻转发生的根源，并参考著名的实时CORBA实现——TAO——阐述了相应的解决方案，主要有非共享的资源分配方式、请求的动态分发和散列等。