A new language concept for high-level distributed programming is proposed. Programs are organised as a collection of concurrently executing processes. Some of these processes, referred to as liaison processes, have a monitor-like structure and contain ports which may be invoked by other processes for the purposes of synchronisation and communication. Synchronisation is achieved by conditional activation of ports and also through port control constructs which may directly specify the execution ordering of ports. These constructs implement a path-expression-like mechanism for synchronisation and are also equipped with options to provide conditional, non-deterministic and priority ordering of ports. The usefulness and expressive power of the proposed concepts are illustrated through solutions of several representative programming problems. Some implementation issues are also considered.

Existing data-flow languages are incapable of supporting large, manageable and reliable non-deterministic programs. Operating system implementations and real-time applications require high-level non-deterministic programming facilities. Hoare's Communicating Sequential Processes and Brinch Hansen's Distributed Processes are two widely acclaimed distributed programming languages for conventional distributed computing systems. The powerful constructs of interprocess communication and synchronisation supported by the above two languages have been incorporated in Communicating Data Flow Channels (CDFC), and Distributed Data Flow Channels (DDFC), two languages proposed in this paper for distributed processing in data-flow systems. Several new features have been incorporated in these languages to make their execution more efficient in a data-flow environment. The implementation of these two languages on an abstract data-flow machine is investigated in detail. Two simulators have been implemented for testing the effectiveness of our implementation schemes for these two data-flow languages. These simulators are written in Pascal and run on a DEC 1090 computing system. This work demonstrates that a data-flow computing system can accommodate, without taking resort to specialised hardware units, the non-deterministic and synchronisation constructs of conventional languages with the attendant benefits of parallel data-driven execution.