Runtime Checking of Datatype Signatures in MPI

Abstract. The MPI standard provides a way to send and receive com-plex combinations of datatypes (e.g., integers and doubles) with a single communication operation. The MPI standard species that the type sig-nature, that is, the basic datatypes (language-dened types such as int or DOUBLE PRECISION), must match in communication operations such as send/receive or broadcast. Because datatypes may be dened by the user in MPI, there is a limitless collection of possible type signatures. Detecting the programmer error of mismatched datatypes is dicult in this case; detecting all errors essentially requires sending a complete de-scription of the type signature with a message. This paper discusses an alternative: send the value of a function of the type signature so that (a) identical type signatures always give the same function value, (b) dif-ferent type signatures often give dierent values, and (c) common cases (e.g., predened datatypes) are handled exactly. Thus, erroneous pro-grams are often (but not always) detected; correct programs never are agged as erroneous. The method described is relatively inexpensive to compute and uses a small (and xed, independent of the complexity of the datatype) amount of space in the message envelope.