Ada Binding to a Shared Object Layer

CORSO, a coordination system for virtual shared memory, allows bindings to different programming languages. Currently C, C++, Java, VisualBasic, and Oracle’s Developer2000 are supported. We implement an Ada binding to CORSO, thus opening the area of virtual shared memory to the Ada world. Our Ada CORSO binding enhances Ada with transaction-oriented, fault-tolerant, distributed objects in a straight-forward way without having to extend the Ada language. 1 A Layered Approach In distributed and heterogeneous environments some technique is desirable to shield the attributes of distributed objects like location, replication, representation and persistency from the programmer. Different approaches exist and the relation between them points to some kind of orthogonality. The most common pattern seem to be the message passing versus virtual shared memory (VSM) paradigm. VSM neither intends to replace nor to exclude message passing architectures like CORBA or DCOM. In contrast, VSM should be seen as an additional layer providing enhanced mechanisms to the programmer. Specifically in Ada’s case, a binding to a VSM increases functionality and facilitates developing distributed applications, despite the fact that a variety of Ada built-in features and annexes in the Ada standard are available. The following issues are to mention: – Communication, data sharing, and persistence has not to be implemented by means of standard Ada but can be put under coordination of a VSM system where several other languages and system architectures are glued together. – The symmetric property of a VSM covers the actual needs of an application well. Particular subtasks can be implemented by the best-suited language, e.g. core development in Ada for safety critical parts and GUI development using Java. The remaining paper is organised as follows: Section 2 overviews shared object paradigms. Section 3 presents concepts of CORSO, a virtual shared object layer developed at the Institute of Computer Languages at the Technical University Vienna and now made available commercially by Tecco Coordination M. González Harbour and J.A. de la Puente (Eds.): Ada-Europe’99, LNCS 1622, pp. 263–274, 1999. c © Springer-Verlag Berlin Heidelberg 1999 264 J. Blieberger, J. Klasek, and E. Kühn Systems, Vienna. Technical aspects of CORSO are revealed in Section 4. Our Ada binding to CORSO is described in Section 5. Pros and cons of our binding can be found in Section 6 where we also compare our binding to other language bindings and conclude the paper. There have been other implementations of VSM in Ada, namely of the Linda tuple space (cf. [5,6,7]). All these implementations are stand-alone Ada implementations which lack the multi-language support of CORSO. In addition, the features offered by Linda are only a subset of CORSO’s functionality.