An Object-Oriented Model for Extensible Concurrent Systems: the Composition-Filters Approach

Applying the object-oriented paradigm for the development of large and complex software systems offers several advantages, of which increased extensibility and reusability are the most prominent ones. The object-oriented model is also quite suitable for modeling concurrent systems. However, it appears that extensibility and reusability of concurrent applications is far from trivial. The problems that arise, the so-called inheritance anomalies are analyzed and presented in this paper. A set of requirements for extensible concurrent languages is formulated. As a solution to the identified problems, an extension to the object-oriented model is presented; composition filters. Composition filters capture messages and can express certain constraints and operations on these messages, for example buffering. In this paper we explain the composition filters approach, demonstrate its expressive power through a number of examples and show that composition filters do not suffer from the inheritance anomalies and fulfill the requirements that were established

The AI Bus architecture for distributed knowledge-based systems

The AI Bus architecture is layered, distributed object oriented framework developed to support the requirements of advanced technology programs for an order of magnitude improvement in software costs. The consequent need for highly autonomous computer systems, adaptable to new technology advances over a long lifespan, led to the design of an open architecture and toolbox for building large scale, robust, production quality systems. The AI Bus accommodates a mix of knowledge based and conventional components, running on heterogeneous, distributed real world and testbed environment. The concepts and design is described of the AI Bus architecture and its current implementation status as a Unix C++ library or reusable objects. Each high level semiautonomous agent process consists of a number of knowledge sources together with interagent communication mechanisms based on shared blackboards and message passing acquaintances. Standard interfaces and protocols are followed for combining and validating subsystems. Dynamic probes or demons provide an event driven means for providing active objects with shared access to resources, and each other, while not violating their security

A metaobject architecture for fault-tolerant distributed systems : the FRIENDS approach

The FRIENDS system developed at LAAS-CNRS is a metalevel architecture providing libraries of metaobjects for fault tolerance, secure communication, and group-based distributed applications. The use of metaobjects provides a nice separation of concerns between mechanisms and applications. Metaobjects can be used transparently by applications and can be composed according to the needs of a given application, a given architecture, and its underlying properties. In FRIENDS, metaobjects are used recursively to add new properties to applications. They are designed using an object oriented design method and implemented on top of basic system services. This paper describes the FRIENDS software-based architecture, the object-oriented development of metaobjects, the experiments that we have done, and summarizes the advantages and drawbacks of a metaobject approach for building fault-tolerant system

Reusable aspect-oriented implementations of concurrency patterns and mechanisms

In this paper, we present a collection of well-known high-level concurrency patterns and mechanisms, coded in AspectJ. We discuss benefits of these implementations relative to plain Java implementations of the same concerns. We detect benefits from using AspectJ in all the cases presented, in the form of higher modularity, reuse, understandability and unpluggability. For most of the implementations, two alternatives can be used: one based on traditional pointcut interfaces and one based on annotations.Fundo Europeu de Desenvolvimento Regional (FEDER).Fundação para a Ciência e a Tecnologia (FCT) - PPC-VM Project POSI/CHS/47158/2002; Project SOFTAS (POSI/EIA/60189/2004)

Application of Cognitive Systems Engineering Approach to Railway Systems (System for Investigation of Railway Interfaces)

This chapter presents the results of a cognitive systems engineering approach applied to railway systems. This application is through the methodology of ’System for Investigation of Railway Interfaces – SIRI’. The utility of the chapter lies in highlighting errors in the current approaches to safety risk management

A Study of Concurrency Bugs and Advanced Development Support for Actor-based Programs

The actor model is an attractive foundation for developing concurrent applications because actors are isolated concurrent entities that communicate through asynchronous messages and do not share state. Thereby, they avoid concurrency bugs such as data races, but are not immune to concurrency bugs in general. This study taxonomizes concurrency bugs in actor-based programs reported in literature. Furthermore, it analyzes the bugs to identify the patterns causing them as well as their observable behavior. Based on this taxonomy, we further analyze the literature and find that current approaches to static analysis and testing focus on communication deadlocks and message protocol violations. However, they do not provide solutions to identify livelocks and behavioral deadlocks. The insights obtained in this study can be used to improve debugging support for actor-based programs with new debugging techniques to identify the root cause of complex concurrency bugs.Comment: - Submitted for review - Removed section 6 "Research Roadmap for Debuggers", its content was summarized in the Future Work section - Added references for section 1, section 3, section 4.3 and section 5.1 - Updated citation

From Procedures, Objects, Actors, Components, Services, to Agents -- A Comparative Analysis of the History and Evolution of Programming Abstractions

The objective of this chapter is to propose some retrospective analysis of the evolution of programming abstractions, from {\em procedures}, {\em objects}, {\em actors}, {\em components}, {\em services}, up to {\em agents}, %have some compare concepts of software component and of agent (and multi-agent system), %The method chosen is to by replacing them within a general historical perspective. Some common referential with three axes/dimensions is chosen: {\em action selection} at the level of one entity, {\em coupling flexibility} between entities, and {\em abstraction level}. We indeed may observe some continuous quest for higher flexibility (through notions such as {\em late binding}, or {\em reification} of {\em connections}) and higher level of {\em abstraction}. Concepts of components, services and agents have some common objectives (notably, {\em software modularity and reconfigurability}), with multi-agent systems raising further concepts of {\em autonomy} and {\em coordination}. notably through the notion of {\em auto-organization} and the use of {\em knowledge}. We hope that this analysis helps at highlighting some of the basic forces motivating the progress of programming abstractions and therefore that it may provide some seeds for the reflection about future programming abstractions.Comment: This preprint has been published as a chapter of a book about the French school of programming, coordinated by Bertrand Meyer and published by Springer in 202

Toward Scalable Parallel Software: An Active Object Model and Library to Support von Neumann Languages

Scalable parallel processing has been proposed as the technology scientists and engineers can use today to solve the problems of tomorrow. Many computational Grand Challenge problems require between two and three orders of magnitude than can be provided with the scalable parallel hardware of the early nineteen-nineties. While hardware continues to become more scalable and cheaper, software is not advancing at the same pace and remains a very expensive part of systems development. A great deal of emphasis on software technology to support scalable parallel processing is placed on von Neumann languages. One of two approaches is common: (a) augment the von Neumann language with explicit parallel constructs or (b) write super-optimizing compilers to “find” the parallelism in a von Neumann program. These two approaches appear to be useful at some level; however, this paper argues that software constructed using these approaches is not likely to scale very well, because an appropriate level of abstraction is not being used to solve the problem. We propose a simple layered architecture for doing parallel processing. The outer layer is the composition layer. This layer is used from a von Neumann language to encode algorithms using standard building blocks (objects). The middle layer uses objects. These objects exhibit high potential for parallelism. In our application, we focus on multidimensional arrays. At the lowest level, Itinerant Actors is used. Itinerant Actors is an object model developed by Christopher and Thiruvathukal at IIT to support asynchronous message-passing between active objects with a number of other useful ideas

Incrementally developing parallel applications with AspectJ

This paper presents a methodology to develop more modular parallel applications, based on aspect oriented programming. Traditional object oriented mechanisms implement application core functionality and parallelisation concerns are plugged by aspect oriented mechanisms. Parallelisation concerns are separated into four categories: functional or/and data partition, concurrency, distribution and optimisation. Modularising these categories into separate modules using aspect oriented programming enables (un)pluggability of parallelisation concerns. This approach leads to more incremental application development, easier debugging and increased reuse of core functionality and parallel code, when compared with traditional object oriented approaches. A detailed analysis of a simple parallel application - a prime number sieve - illustrates the methodology and shows how to accomplish these gains.Fundo Europeu de Desenvolvimento Regional (FEDER) - PPC-VM project POSI/CHS/47158/2002.Fundação para a Ciência e a Tecnologia (FCT) - PPC-VM project POSI/CHS/47158/2002