[MPIWG Fortran] Question on Fortran binding errata

[Junchao Zhang]

Got it.  It is very helpful.
I now understand that we do overloading in MPI since Fortran standards have
different supports for choice buffers. Application programmers only care
interface names; tool developers need to know inner names to intercept. So
MPI spec defines both.




--Junchao Zhang


On Wed, Feb 12, 2014 at 4:28 PM, Jeff Squyres (jsquyres) <jsquyres at cisco.com
> wrote:

> There's deep Fortran voodoo here.  :-)
>
> The short version is that Fortran overloads functions sorta similar to
> C++, but with a different mechanism.  So you can:
>
>     call foo(integer_value)
> and
>     call foo(floating_value)
>
> and have it call 2 different back-end subroutines, just like C++.  The way
> this is done in fortran is with interfaces.  Something like this:
>
> interface foo
>    subroutine foo_integer(a)
>        integer :: a
>    end subroutine foo_integer
>
>    subroutine foo_real(a)
>        real :: a
>    end subroutine foo_real
> end interface foo
>
> So you've declared one interface -- foo -- but with 2 different subroutine
> implementations -- foo_integer and foo_real (note that the above is a
> *declaration*, it is not an *implementation*).  You can then go implement
> foo_integer and foo_real, and the compiler will take care of figuring out
> which actual subroutine to invoke when an application invokes "call foo(x)".
>
> The "specific procedure name" refers to the "inner" names (e.g.,
> foo_integer and foo_real, in this example).  As Craig said, because of the
> MPI profiling layer, we mandated specific forms of specific procedure
> names.  Otherwise, 3rd party tools wouldn't be able to intercept calls via
> the MPI profiling mechanism (because the actual/back-end symbol for any
> given procedure would be unknown / implementation-specific).
>
> Make sense?
>
>
> On Feb 12, 2014, at 5:02 PM, Craig Rasmussen <rasmus at cas.uoregon.edu>
> wrote:
>
> > We realized after working on MPI-3 for awhile that we would need Fortran
> wrappers and couldn't really call C routines directly.  One of the reasons
> is that the MPI C routines return a function value and most of the Fortran
> bindings are subroutines without a return value.  The language you refer to
> is a requirement on the implementer as to what the name of the wrapper
> routine is.
> >
> > For example, if the user calls MPI_Isend and uses the MPI_F08 module,
> then the wrapper routine shall (must) be called MPI_Isend_f08.  Another
> requirement we have placed on implementors is that the wrapper name can't
> be hidden within a module so that Fortran module name mangling won't be
> done for the MPI_Isend_f08 routine.
> >
> > Craig Rasmussen
> > CAS Scientific Programmer
> > rasmus at cas.uoregon.edu
> >
> >
> >
> >
> > On Feb 12, 2014, at 1:28 PM, Junchao Zhang wrote:
> >
> >> Hello,
> >>   On page 10, line 38 of the errata,
> http://www.mpi-forum.org/docs/mpi-3.0/errata-30.pdf, it reads
> >>
> >> A Fortran call to an MPI routine shall result in a call to a procedure
> with one of the
> >> specific procedure names and calling conventions, as described in Table
> 1.1 on page 11.
> >> Case is not significant in the names.
> >>
> >>    Can someone explain it a little more, especially, what is the
> meaning of "specific procedure names"?
> >>    Thank you.
> >>
> >> --Junchao Zhang
> >> _______________________________________________
> >> mpiwg-fortran mailing list
> >> mpiwg-fortran at lists.mpi-forum.org
> >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
> >
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>
>
> --
> Jeff Squyres
> jsquyres at cisco.com
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
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