Dear MPI Forum,
The description of the 'array_of_commands` parameter passed to
'MPI_Comm_spawn_multiple()' is not crystal clear IMHO.
The standard simply states
MPI_COMM_SPAWN_MULTIPLE(count, array_of_commands, ...)
IN count number of commands (positive integer, significant to MPI
only at root | see advice to users)
IN array_of_commands programs to be executed (array of strings,
significant only at root)
Advice to users. The argument count is interpreted by MPI only at
the root, as is
array_of_argv. Since the leading dimension of array_of_argv is
count, a non-positive
value of count at a non-root node could theoretically cause a
runtime bounds check
error, even though array_of_argv should be ignored by the
subroutine. If this happens,
you should explicitly supply a reasonable value of count on the
non-root nodes. (End
of advice to users.)
And the Fortran binding is
MPI_COMM_SPAWN_MULTIPLE(COUNT, ARRAY_OF_COMMANDS, ...)
INTEGER COUNT
CHARACTER*(*) ARRAY_OF_COMMANDS(*)
Intuitively, it seems obvious that 'array_of_commands' is an array of
'count' commands.
That being said, the standard does not state that, and it is unclear
whether 'array_of_commands' should be
NULL-terminated (so to speak) or not.
Back to the Fortran binding, the following prototype, which is somehow
consistent with 'array_of_argv',
could (help to) clear the confusion. The same comments also apply to the
Fortran 2008 binding.
CHARACTER*(*) ARRAY_OF_COMMANDS(COUNT)
Gilles
