5.3.2.0.4 The info argument

The info argument to all of the routines in this chapter is an opaque handle of type MPI_Info in C, MPI::Info in C++ and INTEGER in Fortran. It is a container for a number of user-specified (key,value) pairs. key and value are strings (null-terminated char* in C, character*(*) in Fortran). Routines to create and manipulate the info argument are described in Section 4.10 on page [*].

For the SPAWN calls, info provides additional (and possibly implementation-dependent) instructions to MPI-/ and the runtime system on how to start processes. An application may pass MPI_INFO_NULL in C or Fortran. Portable programs not requiring detailed control over process locations should use MPI_INFO_NULL.

MPI-/ does not specify the content of the info argument, except to reserve a number of special key values (see Section 5.3.4 on page [*]). The info argument is quite flexible and could even be used, for example, to specify the executable and its command-line arguments. In this case the command argument to MPI_COMM_SPAWN could be empty. The ability to do this follows from the fact that MPI-/ does not specify how an executable is found, and the info argument can tell the runtime system where to ``find'' the executable ``'' (empty string). Of course a program that does this will not be portable across MPI-/ implementations.

MPI-Standard for MARMOT