Abstract This paper presents a model of concurrent object-oriented programming in which specification of computational behavior is separated from specification of interac-tion behavior of methods. It will be shown that this compositional approach to concurrent programming avoids someof the conceptual difficulties that have plagued the integration of concurrency and object-oriented models of pro-grams. The compositional approach to concurrent objectoriented programming leads to declarative and incremen-tal specification of interaction behavior and thus, to object/method definitions that can be readily adapted to dif-ferent parallel execution environments. The approach supports inheritance of both method and synchronization spec-ifications. It will be shown that compositional programming avoids the so-called "inheritance anomaly."

In many concurrent programming languages programs are difficult to extend and modify. This is because changes in a concurrent program (either through modification or extension) require re-implementation of some or all components. This paper presents the design of a concurrent object-oriented programming language based upon separate specifications of computations and interactions of programs. Separate specification of computations and interactions allows each to be separately modified and extended. We show that separation also facilitates extension of other language composition mechanisms such as class, inheritance, and template in order to define concurrent program abstractions. The resulting language supports extensibility and modifiability of concurrent programs as well as reusability of specifications of computations and interactions. 1

There is significant interest in concurrent programming due to widespread availability of parallel and distributed systems. The design and implementation of concurrent programs for the parallel and distributed systems has proven to be extremely difficult. Concurrent programs are difficult to design, implement, and maintain because changes in a concurrent program (through addition of new components or modification of existing components) requires re-implementation of some or all components. Also, it is difficult to reuse specifications of components and interactions. Concurrent object-oriented programming languages show promise in alleviating the modularity and extensibility problems. Concurrent objects form a natural basis for modeling entities of applications. Further, extensibility is naturally supported through the notion of inheritance. Many object-oriented programming languages [3, 5, 1, 2] have been proposed that extend a sequential object-oriented programm