Hi, Matthias Troyer wrote:
On Sep 17, 2006, at 7:56 PM, Robert Ramey wrote: [...]
Note that you've used packed_archive - I would use mpi_archive instead. I think this is a better description of what it is.
I still prefer mpi::packed_archive, since there can also be other MPI archives. One possible addition to speed up things on homogeneous machines might be just an mpi::binary_archive, using a binary buffer.
Yes, this is a realistic idea; almost all MPI programs are run on homogeneous clusters anyway. Even in a heterogeneous environment there remains the question as to whether one can do better than MPI_Pack/Unpack by using some kind of 'portable' archive (although 'transportable' might be a better word). In principle the answer is definitely yes, as the conversion functions can be inlined. [...]
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... Cheers, Ian