Triveni: Basis

Triveni is a programming methodology for concurrent programming with threads and events. Triveni has its basis in process algebras (e.g., CCS [Mil89], CSP [Hoa85]) and synchronous programming languages (e.g., see [Hal93]). The key feature of these formalisms is a notion of abstract behavior, which in a concurrent system is essentially the interaction of the system with its environment. Communication is via (labeled) events that are abstractions of names of communication channels. Triveni has the following features:

• Programs can be combined freely with the Triveni combinators, and one need only be concerned about the desired effects on the resulting behavior. Thus, Triveni combinators operate on behaviors and the result of the combinators are behaviors: the implementation of Triveni yields the correct combination of behaviors.

• Triveni enables parallel composition to be used freely for the modular decomposition of designs. In particular, the parallel composition of Triveni programs yields programs that are indistinguishable from simple ones (in much the same way that an object built by object composition has the same status as a simple object).

  The correct wiring among events sent by parallel components is done automatically by Triveni, and thus, the implementation of a program can closely reflect its design. Namely, each parallel component can be implemented separately: Triveni realizes the desired communication among them.

• Triveni supports exceptions via preemption combinators. For example, the watchdog combinator DO P WATCHING e yields a process that behaves like P until event e happens, upon which execution of P is terminated (in the spirit of ``Ctrl-C''). Analogous to exception mechanisms in traditional programming languages, the preemption combinators aid in program modularity; for example, the watchdog above avoids the pollution of P with information about the event e.

  In Triveni, exceptions have first class status -- any event can be an exception and can be used in the place of e in the watchdog. This allows exceptions to play an integral role in in the programming of systems.

  Priorities on events are achieved by nesting of the preemption operators; for example, the event e2 has higher priority than the event e1 in the program fragment DO (DO P WATCHING e1) WATCHING e2. These priorities are not fixed by Triveni; they are determined by the program/design text.

• Triveni is compatible with the extensive existing work in both the design and implementation of programming languages and the analysis of concurrent systems. In particular, Triveni integrates the aforementioned ideas into the context of object oriented programming. Furthermore, Triveni is compatible with existing threads standards such as Pthreads and Java threads, and with event models structured on the Observer pattern [GHJV95]. Finally, Triveni includes a specification-based testing environment that automates testing of safety properties.