Synchronous C++: A Language for Interactive Applcations

D eveloped at the Ecole Polytechnique Fédérale of Lausanne, Switzerland, Synchronous C++ has strong connections to the domains of concurrency, behavior analysis, and OO programming. Namely, sC++ contains a real-time kernel, lends itself to analysis by modern modeling and analysis theories, 1-3 and uses the same syntax for active objects as for passive ones. Understanding the relationship of concurrency to general OO programming is essential for understanding the benefits of sC++. To help clarify this relationship , let's focus on the OMT/Rumbaugh 4 OO technique. According to this method, application development should proceed in three phases: analysis, design, and implementation. The analysis phase produces three models—object, dynamic, and functional—while the design phase builds on these models to prepare for the implementation phase. The object model specifies the data components pertinent to the application, their attributes, and the operations that characterize them. The dynamic model specifies operation sequence using state diagrams. The functional model uses dataflow diagrams to specify data inputs and outputs, sources and sinks, and the location of transmission and reception. Basically, the object model describes the data while the other two models describe aspects that are usually related to con-currency. The aspects captured in the functional model are closely related to message passing and parallelism. OO languages such as C++ provide good support for implementing the object model, but their support for implementing the dynamic and functional models is not so good. In fact, it requires significant programmer involvement. sC++ makes the implementation of these two models much more straightforward. In this article, I focus on examples in which the dynamic and functional models dominate and the object model is secondary. In doing so, I propose a mapping between the elements of all three models and sC++ statements. Several other concepts have been proposed to extend OO languages to concurrency: delayed evaluations (a concept that proposes to launch each method on a separate thread, as in Actors 5), processes orthogonal to the objects (Ada), asynchronous channels and exceptions (Eiffel 6), and others. However, the researchers who proposed these solutions emphasized the improvements of speed they expected from achieving concurrency, rather than the characteristics that make concurrency suitable for the analysis and the implementation of specifications such as the ones provided by models. sC++ introduces the concept of an active object. The syntax of the definition, instantiation, reference, call, inheritance, and deletion of an active object is identical to …