Mm,
OpenMPI functions like MPI_Irecv, does pointer arithmetics over recv
buffer using type info in ompi_datatype_t i suppose. I'm trying to
write a wrapper to MPI_Gather using Irecv functions:
int MPI_FT_Gather(void*sendbuf, int sendcount, MPI_Datatype sendtype,
void*recvbuff,
int recvcount, MPI_Datatype recvtype,
int root, MPI_Comm comm){
...
for( nprocs..){
MPI_Irecv(&recvbuff[(i-1)], recvcount, recvtype, i, 0, comm,
&array_request[i-1]);
}
}
where every proc sends 1 double. It doesn't work,( received values are
wrong) because MPI_Irecv are trying to do pointer arithmetic with void
values. In fact, if i write:
double*buff = &recvbuff[0];
for( nprocs..){
MPI_Irecv(&buff[(i-1)], recvcount, recvtype, i, 0, comm, &array_request[i-1]);
}
it works well. Do you have an idea to use a portalbe way to do this?(
if is it possible)
2009/3/30 Massimo Cafaro <massimo.caf...@unisalento.it>:
> Dear Gabriele,
>
> to the best of my knowledge the MPI standard does not provide such a
> function.
> The reason is that when calling MPI_Gather, the standard requires matching
> type signatures (i.e., the sendcount and sendtype argument on each of the
> non root processes must match the recvcount and recvtype arguments at the
> root process). This still allows having disting type maps (type and
> displacement pairs) at a sender process and at the root process, but it is a
> feature seldom used in practice, at least in my experience.
>
> Therefore, you must know in advance the datatype you are receiving even in
> the case this datatype is a derived datatype.
> If not, the likely outcome is that the receive buffer at the root process
> gets overwritten, which causes MPI_Gather to return an error.
>
> Due to the signature of the MPI_Gather function, the only possibility I see
> to achieve what you are trying to do is to use the MPI_BYTE datatype, and
> use the communicator argument to distinguish between a collective gather in
> which you receive MPI_INT, MPI_DOUBLE etc. Of course I would not create nor
> recommend to create new communicators for this purpose only.
>
> Kind regards,
> Massimo
>
> On 30/mar/09, at 17:43, Gabriele Fatigati wrote:
>
>> Dear OpenMPI developers,
>> i'm writing an MPI_Gather wrapper to collect void elements. My
>> queation is: is there a portable way to know the type of received
>> elements, like MPI_INT or MPI_DOUBLE? I've noted that i can retrieve
>> this information by ompi_datatype_t-> name field, but i think isn't
>> portable. Is there aMPI function that does this check?
>>
>> --
>> Ing. Gabriele Fatigati
>>
>> Parallel programmer
>>
>> CINECA Systems & Tecnologies Department
>>
>> Supercomputing Group
>>
>> Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
>>
>> www.cineca.it Tel: +39 051 6171722
>>
>> g.fatigati [AT] cineca.it
>> _______________________________________________
>> users mailing list
>> us...@open-mpi.org
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
>
> --
>
> *******************************************************************************************************
>
> Massimo Cafaro, Ph.D. Additional affiliations:
> Assistant Professor National
> Nanotechnology Laboratory (NNL/CNR-INFM)
> Dept. of Engineering for Innovation Euro-Mediterranean Centre for
> Climate Change
> University of Salento, Lecce, Italy SPACI Consortium
> Via per Monteroni E-mail
> massimo.caf...@unisalento.it
> 73100 Lecce, Italy
> caf...@ieee.org
> Voice +39 0832 297371
> caf...@acm.org
> Fax +39 0832 298173
> Web http://sara.unisalento.it/~cafaro
>
> *******************************************************************************************************
>
>
>
> _______________________________________________
> users mailing list
> us...@open-mpi.org
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
--
Ing. Gabriele Fatigati
Parallel programmer
CINECA Systems & Tecnologies Department
Supercomputing Group
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it Tel: +39 051 6171722
g.fatigati [AT] cineca.it
