[mpiwg-tools] PMPI for a complete MPI wrapper

Wed Oct 4 06:36:29 CDT 2017

Hello Jean-Baptiste,

thanks for the fast answer. With the pmpi.h I mean a file like mpi.h but only containing the PMPI_ Interface. As you suggested I might try to create a full wrapper myself. I took a look on the wi4mpi project and there approach seems to create there own interface aka. mpi.h and then wrap this to the intel MPI or OpenMPI implementation. Due to this approach, they know the data types and can generate the interface.

In my library I wanted to use a light wight wrapper. That is I wanted to use the original data types. With this approach I currently have structures like:

struct AMPI_Comm {
// my own data;
MPI_Comm comm; // the original object
};

I can then simply call the pmpi functions with the stored original object.
If I have a wrapper such that there is a PMPI_Comm object available, I could do the following:
struct MPI_Comm {
// my own data;
PMPI_Comm comm; // the original object
};

If the wrapper should use the same types from a general mpi.h, then I do not know the types and would need to declare something like:

hidden_mpi.c
#include <mpi.h>
decltype(MPI_COMM_WORLD) PMPI_COMM_WORLD = MPI_COMM_WORLD;

and then I need to use PMPI_COMM_WORLD in my library and I can generate a hmpi.h wich contains lines like:
#define MPI_COMM_WORLD PMPI_COMM_WORLD

Which could be included by the user. But in order use PMPI_* in my library, I need to specify the symbol in a header file for which I need the type. In order to get the type I need to include mpi.h which will define MPI_COMM_WORLD and I have a name clash.

So unfortunately I see no way in providing a wrapper without writing a complete MPI Interface, which I would like to avoid. I might be able to use the wi4mpi Project and use there interface as a base for my implementation, which would add a dependency to my project.

A third and very ugly option would be, that I define all my types as void* in the interface for the user. But this disables type checking and I still would need to wrap from void* to references of my types.

So I might just stay in my AMPI namespace and provide a macro for the user to either call regular mpi functions or my wrapper functions.

Cheers

Max

On Wed, 2017-10-04 at 11:00 +0200, Jean-Baptiste BESNARD wrote:
Dear Max,

I’m not sure I completely understand what you mean by a « pmpi.h » however I may have some initial elements below.

The PMPI interface is currently targeting MPI functions only and indeed some of the values you’ll find in your executable will be compile time constants.
In fact, most MPI types/Constants are implementation dependent, there is no unified ABI.

Nonetheless, you might be able to interpret them in your wrapper library in order to have them « rerouted » to your target implementation.
I mean, knowing the value of MPI_COMM_WORLD you could rewrite it to be MPI_COMM_WORLD2.
And for sure you wont’t find a PMPI_COMM_WORLD.

I can help on writing a wrapper for the whole PMPI interface. See my repo here: https://github.com/besnardjb/mpi-snippets
There is a simple python script generating VIM snippets for MPI from JSON specs, it can easily be converted to a script generating the whole MPI interface.

Eventually, an approach close to what you want to do might be https://github.com/cea-hpc/wi4mpi which operates this systematic handler conversion between MPI flavors, but this clearly involves some rewriting.

Hope this helps.

Regards,

Jean-Baptiste.

Le 4 oct. 2017 à 10:35, Max Sagebaum <max.sagebaum at scicomp.uni-kl.de<mailto:max.sagebaum at scicomp.uni-kl.de>> a écrit :

Hello @ all,

my question is concerning the PMPI specification. I hope the list is the correct place to ask.

I want to write a complete wrapper for MPI. That is every define, typedef and function will be wrapped and might be completely changed. Currently I prefixed everything with AMPI_ such that no name clashes exist. But the user would need to rename every occurrence of MPI_ with AMPI_

I would now like to use the PMPI definition of MPI to define my wrappers as the MPI version which then use the PMPI definitions. Unfortunately I could not find tutorials for a complete wrapper.

As an example take MPI_COMM_WORLD. I made a grep on the openmpi installation on my linux machine for PMPI_COMM_WORLD but the result was empty. The definition of MPI_COMM_WORLD was
#define MPI_COMM_WORLD OMPI_PREDEFINED_GLOBAL( MPI_Comm, ompi_mpi_comm_world)
without any chance to switch to PMPI_COMM_WORLD as a predefined macro.

I also checked the newest source tarball of openmpi and I could not find anything for PMPI_COMM_WORLD there.

In the mpi 3.0 standard on page 555 in section 14.2.1 the requirements are just listed for functions. Was the definition of the PMPI_ supplements for defines, types etc. never discussed?

I would have expected, that I can just include a pmpi.h and then I would have all the PMPI_ symbols without the MPI symbols available.

Do you know of any way I could make my idea work?

Cheers

Max

--

Max Sagebaum Chair for Scientific Computing, TU Kaiserslautern, Bldg/Geb 34, Paul-Ehrlich-Strasse, 67663 Kaiserslautern, Germany Phone: +49 (0)631 205 5638 Fax: +49 (0)631 205 3056 Email: max.sagebaum at scicomp.uni-kl.de<mailto:max.sagebaum at scicomp.uni-kl.de> URL: www.scicomp.uni-kl.de<http://www.scicomp.uni-kl.de>

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Max Sagebaum Chair for Scientific Computing, TU Kaiserslautern, Bldg/Geb 34, Paul-Ehrlich-Strasse, 67663 Kaiserslautern, Germany Phone: +49 (0)631 205 5638 Fax: +49 (0)631 205 3056 Email: max.sagebaum at scicomp.uni-kl.de URL: www.scicomp.uni-kl.de
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