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