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Subject: Re: [OMPI users] Configure and Build ok, but mpi module not recognized?
From: Brian Harker (brian.harker_at_[hidden])
Date: 2008-09-22 20:36:48

Nope, no user-defined types or arrays greater than 2 dimensions.

On Mon, Sep 22, 2008 at 6:24 PM, Jeff Squyres <jsquyres_at_[hidden]> wrote:
> On Sep 22, 2008, at 6:48 PM, Brian Harker wrote:
>> when I compile my production code, I get:
>> fortcom: Error: driver.f90: line 211: There is no matching specific
>> subroutine for this generic subroutine call. [MPI_SEND]
>> Seems odd that it would spit up on MPI_SEND, but has no problem with
>> MPI_RECV... What do you guys think? And thanks again for your help
>> and patience?
> The F90 MPI bindings have some well-known design flaws (i.e., problems with
> the standard itself, not any particular implementation). Many of them
> center around the fact that F90 is a strongly-typed language. See this
> paper for some details:
> Here's the highlights, as they pertain to writing F90 MPI apps:
> - There is no equivalent to C's (void*). This means that the F90 MPI
> bindings cannot accept user-defined datatypes.
> - This also means that *every* pre-defined type must have a F90 MPI binding.
> There are approximately 15 intrinsic size/type combinations. There are 50
> MPI functions that take one choice buffer (e.g., MPI_SEND, etc.), and 25
> functions that take two choice buffers (e.g., MPI_REDUCE). I'm copying this
> math from the paper, and I think we got it slightly wrong (there was a
> discussion about it on this list a while ago), but it results in many
> *millions* of F90 MPI bindings functions. There's no compiler on the planet
> than can handle all of these in a single F90 module.
> Open MPI compensates for this with the following:
> - F90 bindings are not created for any of the 2-choice-buffer functions
> - F90 bindings are created for all the 1-choice-buffer functions, but only
> for dimensions up to N dimensions (N defaults to 4, IIRC). You can change
> the value of N with OMPI's configure script; use the
> --with-f90-max-array-dim. The maximum value of N is 7.
> So -- your app failed to compile because you either used a user-defined
> datatype or you used an array with a dimension greater than 4. If it was a
> greater-dimension issue, you can reconfigure/recompile/reinstall OMPI
> (again, sorry) with a larger N value. If it was a user-defined datatype,
> you unfortunately have to "include mpif.h" in that
> subroutine/function/whatever, sorry (and you lose the type checking). :-(
> Here's some info from OMPI's README:
> -----
> - The Fortran 90 MPI bindings can now be built in one of three sizes
> using --with-mpi-f90-size=SIZE (see description below). These sizes
> reflect the number of MPI functions included in the "mpi" Fortran 90
> module and therefore which functions will be subject to strict type
> checking. All functions not included in the Fortran 90 module can
> still be invoked from F90 applications, but will fall back to
> Fortran-77 style checking (i.e., little/none).
> - trivial: Only includes F90-specific functions from MPI-2. This
> means overloaded versions of MPI_SIZEOF for all the MPI-supported
> F90 intrinsic types.
> - small (default): All the functions in "trivial" plus all MPI
> functions that take no choice buffers (meaning buffers that are
> specified by the user and are of type (void*) in the C bindings --
> generally buffers specified for message passing). Hence,
> functions like MPI_COMM_RANK are included, but functions like
> MPI_SEND are not.
> - medium: All the functions in "small" plus all MPI functions that
> take one choice buffer (e.g., MPI_SEND, MPI_RECV, ...). All
> one-choice-buffer functions have overloaded variants for each of
> the MPI-supported Fortran intrinsic types up to the number of
> dimensions specified by --with-f90-max-array-dim (default value is
> 4).
> Increasing the size of the F90 module (in order from trivial, small,
> and medium) will generally increase the length of time required to
> compile user MPI applications. Specifically, "trivial"- and
> "small"-sized F90 modules generally allow user MPI applications to
> be compiled fairly quickly but lose type safety for all MPI
> functions with choice buffers. "medium"-sized F90 modules generally
> take longer to compile user applications but provide greater type
> safety for MPI functions.
> Note that MPI functions with two choice buffers (e.g., MPI_GATHER)
> are not currently included in Open MPI's F90 interface. Calls to
> these functions will automatically fall through to Open MPI's F77
> interface. A "large" size that includes the two choice buffer MPI
> functions is possible in future versions of Open MPI.
> -----
> FWIW, we're arguing^H^H^H^H^H^H^Hdiscussing new Fortran 2003 bindings for
> MPI in the MPI-3 Forum right now. We have already addressed the problems
> discussed above (F03 now has an equivalent of (void*)), and hope to do a few
> more minor things as well. There's also discussion of the possibility of a
> Boost.MPI-like Fortran 2003 MPI library that would take advantage of many of
> the features of the language, but be a little farther away from the official
> MPI bindings (see www.boost-org for details about how their nifty C++
> library works on top of MPI).
> --
> Jeff Squyres
> Cisco Systems
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