| Abstract: | The design of a communicating sequential process language is presented, featuring a parallel command, communication by message passing and the use of the guarded command as a means of introducing and controlling non-determinism. The language described here incorporates a number of new proposals regarding communications between sequential processes. The principal proposal is that messages are to be selected for reception by a receiving process solely on the basis of their type and arrival order within type; in particular, the identity of the sending process does not influence message reception. This results in a greater degree of parallelism and non-determinism, which is useful to both the programmer and the language implementor. Also a hierarchichal composition regime is proposed, which gives communications significance to the organization of subprocess hierarchies; this promotes an independence of specification of program components through information hiding properties. The language implementation is described, and several aspects are of particular interest: the design of a process scheduler in a non-deterministic situation leads to some interesting optimizations, as does the design of a message handler in the case where the communicating processes can access the same memory. Finally, example programs are given to illustrate some of the novel features of the language. |
