A Critique of the Programming Language C*

This paper appeared in: Communications of the ACM, 35(6):21--24, June 1992 C* is a data parallel programming language originally developed for the Connection Machine. Efforts are now underway to standardize a revised version of C* [6]. We think that standardization of C* is premature at this time, since the language contains a number of unproven constructs and obvious flaws. We are concerned that standardization of a parallel language now might force its programming model upon future generations of programmers, even though we already know it is deficient. The purpose of this note is to make the relevant issues accessible to a wider audience and to make specific recommendations for improving C*. C* is an extension of ANSI standard C and intended as an "efficient, fairly low-level systems programming language[6]" for parallel computers with distributed memory. Parallelism is expressed directly in the data parallel paradigm. In this paradigm, "parallelism comes from simultaneous operations across large sets of data, rather than from multiple threads of control[2]". Data parallelism is a synchronous paradigm and therefore well suited to SIMD machines. It has also been implemented successfully on a MIMD machine[5]. As an extension of C, C* inherits most of the drawbacks of its ancestor, but we are not concerned about those here. Neither are we concerned with limiting C* to a synchronous paradigm, even though an asynchronous one would be more general. We are concerned, however, with the principles of programming language design, the programming model underlying C*, and the efficient implementability of C* on both SIMD and MIMD machines. The problems we identified in C* in these areas are discussed below