Stuart E. Mitchell

Synchronisation, concurrent object-oriented programming and the inheritance anomaly

There have been a number of models proposed for integrating concurrency and object-oriented programming. Unfortunately, there have been few criteria proposed for evaluating them. In focusing on issues of inheritance, designers of new concurrent object-oriented programming languages appear to have forgotten the experiences learned from over two decades of concurrent programming. In this paper we review Blooms criteria for evaluating the expressive power of synchronisation primitives, and apply it in an object-oriented framework. We show that most of the available concurrent object-oriented programming languages lack expressive power, and that this contributes to the so-called inheritance anomaly. We then propose a new model which does address all of Blooms criteria.

On Programming Atomic Actions in Ada 95

This paper describes the development of two kinds of atomic action schemes for Ada 95. We start by discussing the basic features required of an atomic action scheme and what choices, e.g. between synchronous and asynchronous actions, are appropriate for Ada 95. We then present two implementations of actions; first using Ada 95 packages to create asynchronous actions and secondly, as sets of tasks for synchronous actions. For each action type, we present code fragments illustrating their development and use. Finally, we discuss some related issues (exception resolution, action nesting, state restoration, software re-use and extension, preventing information smuggling, distributed execution) which have been addressed in our work and show some of the problems encountered (the deserter problem, using different sorts of interparticipant communications and resources).

Developing a real-time metaobject protocol

The paper first introduces the concepts of reflection and its use for separating functional and non-functional concerns within a system. The authors then explore the structure and behaviour required of a real-time metaobject protocol and develop a MOP based on scheduling groups. Finally, they present examples of using reflection in real-time systems for the dynamic scheduling of tasks via best-effort scheduling and task-pair scheduling.

Distributed Atomic Actions in Ada 95

This paper discusses the development of a distributed asynchronous atomic action scheme for Ada 95. The scheme makes use of many unique Ada 95 features including protected objects, asynchronous transfer of control and the distributed systems annex. We present the packages which implement the local and global action support and illustrate their use in a (partial) implementation of the FZI production cell problem. We also discuss a number of variations of the model and how these might be included. Finally, we discuss how the distribution model used in Ada 95 has influenced our design.

MOPping up exceptions

This paper describes the development of a model for the reflective treatment of both application and environmentally sourced exceptions. We show how a variety of exception models can be implemented using an exception handler at the metalevel. The approach described allows for better separation of exceptional and normal error-free program code producing systems that are easier to understand and therefore maintain.

ECOOP'98 Workshop on Reflective Object-Oriented Programming and Systems

In recent years the principles of reflective object-oriented programming have seen increasing acceptance and application to a wide range of fields - for example, security, fault tolerance and real time. Reflection is seen as a promising way of managing system complexity by separating functional and non-functional concerns and we believe that many areas of system design and validation can benefit from this research. This workshop was aimed at providing a venue at which researchers into many disparate topics related to reflection could meet, disseminate their ideas to a broad spectrum of the reflection community, and explore the advantages that the disciplined separation of concerns offered by a reflective system can provide within a computing system.

MOPping up Exceptions

This paper describes the development of a reflective treatment of exception handling. It introduces a metaexception object responsible for controlling the semantics of an exception and enabling run-time change of those semantics - for example from the termination to resumption model.

Adaptive Scheduling Using Reflection

This paper presents a model for adaptable scheduling for hard and soft real-time systems that are designed to cope with a variety of situations including unexpected faults, imprecisely defined environments, reconfiguration etc. The model uses scheduling groups (derived from meta-groups as used in ABCL/R) that are responsible for managing shared resources within a set of components. Each group has an independent schedule (for simultaneous soft and hard groups) and many factors can be modified at run-time.

Reflective Real-Time Object-Oriented Programming and Systems

This was the first workshop to be held on this topic at ECOOP and was attended by approximately 15 participants from around the world.

Real-time programming in the concurrent object-oriented language TAO

The paper introduces the concurrent object oriented language TAO and then considers how real time support can be added. The paper describes how concurrent objects can be mapped to sporadic and periodic tasks through inheritance within the concurrent object oriented language TAO.