JCoBox: Generalizing Active Objects to Concurrent Components

Concurrency in object-oriented languages is still waiting for a satisfactory solution. For many application areas, standard mechanisms like threads and locks are too low level and have shown to be error-prone and not modular enough. Lately the actor paradigm has regained attention as a possible solution to concurrency in OOLs. We propose JCoBox: a Java extension with an actor-like concurrency model based on the notion of concurrently running object groups, so-called coboxes. Communication is based on asynchronous method calls with standard objects as targets. Cooperative multi-tasking within coboxes allows for combining active and reactive behavior in a simple and safe way. Futures and promises lead to a data-driven synchronization of tasks. This paper describes the concurrency model, the formal semantics, and the implementation of JCoBox, and shows that the performance of the implementation is comparable to state-of-the-art actor-based language implementations for the JVM.