Re: [boost] [MPI] Review comments

From: Matthias Troyer (troyer_at_[hidden])
Date: 2006-09-18 13:38:35

Hi Ian,

On Sep 18, 2006, at 6:35 PM, Ian McCulloch wrote:
>>> Really its only a name change - and "packed archive" is already
>>> inside an
>>> mpi namespace so its not a huge issue.  BUT I'm wondering if the
>>> idea of
>>> rendering C++ data structures as MPI primitives should be more
>>> orthogonal to
>>> MPI prototcol itself.  That is, might it not be sometimes
>>> convenient to save
>>> such serializations to disk?  Wouldn' this provide a portable
>>> binary format
>>> for free?  (Lots of people have asked for this but no one as been
>>> sufficiently interested to actually invest the required effort).
>>
>> As Doug Gregor pointed out this is not possible since the format is
>> implementation-defined, and can change from one execution to another.
>
> This is only true for MPI-1.1.  MPI-2 supports multiple data  
> representations
> and adds the functions MPI_Pack_external and MPI_Unpack_external to  
> convert
> to/from the "external32" format defined in section 9.5.2 of the MPI-2
> standard.  The intent of this is to be able to transfer data  
> between MPI
> implementations.  Also, as part of the file I/O interface, MPI-2 also
> allows user-defined representations so in principle it would be  
> possible to
> make some kind of adaptor to read a different archive format via  
> the MPI-2
> file I/O.  Not that MPI file I/O seems to be used much anyway...

The current library is based on MPI-1.1 only, which is reasonably  
stable. A future extension of the library to MPI-2 could indeed  
include the use of MPI-I/O to write portable binary archives.

Matthias