Composing concurrent objects

Adopting 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 modelling concurrent systems. However, it appears that extensibility and reusability of concurrent applications is far from trivial. In addition, very little attention has been paid by the conventional object-oriented development methodologies to the analysis and design of\ud synchronisation constraints for concurrent objects.\ud To address these problems, in this thesis the framework of composition-filters, an extension to the object-oriented model, is adopted. An analysis is presented of the problems involved in reusing and extending concurrent objects, in particular the so-called inheritance anomalies. Based on this analysis, a set of criteria for effective extensible concurrent objectoriented\ud programming languages is formulated.\ud The thesis introduces techniques for the creation of concurrency and the synchronisation of concurrent activities, fully integrated within the (object-oriented) composition-filters model. Important properties of the proposed object model are: all objects are -potentially- active, intra-object concurrency is supported and synchronisation specifications are fully separated\ud from method implementations. The applicability and expressive power of the proposed technique are demonstrated, and it is shown how reusability and extensibility of concurrent objects are achieved

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