Safe usage of registers in BSPlib.

Bulk Synchronous Parallel (BSP) is a simple but powerful high-level model for parallel computation. Using BSPlib, programmers can write BSP programs in the general purpose language C. Direct Remote Memory Access (DRMA) communication in BSPlib is enabled using registrations: associations between the local memories of all processes in the BSP computation. However, the semantics of registration is non-trivial and ambiguously specified and thus its faulty usage is a potential source of errors. We give a formal semantics of BSPlib with which we characterize correct registration. Anticipating a static analysis, we give a simplified programming model that guarantees correct registration usage, drawing upon previous work on textual alignment.