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Subject: [OMPI users] How to "guess" the incoming data type ?
From: Sylvestre Ledru (sylvestre.ledru_at_[hidden])
Date: 2010-04-25 09:46:08


Hello,

I am currently extending an application with MPI capabilities.
This high-level application allows users to use dynamic types. Therefor,
on the slaves, I have no way to know what the master will send me.

Therefor, in the slave side, I need to "guess" what I am receiving.

For example, I am using contiguous data on the master defined this way:

MPI_Datatype matrixOfDouble;
MPI_Type_contiguous(size, MPI_DOUBLE, &matrixOfDouble);
MPI_Type_commit(&matrixOfDouble);

sent this way:
double A[] = {1,3,3,2,3,4};
MPI_Send(&A, 1, matrixOfDouble, i, TAG, MPI_COMM_WORLD);

On the slave, in my example, since I know I am going to receive a
matrixOfDouble, I can do the following:
MPI_Probe( MPI_ANY_SOURCE, TAG, MPI_COMM_WORLD, &stat );
MPI_Get_elements( &stat, matrixOfDouble, &count);
double BRecv[count];
MPI_Recv(BRecv, BUFSIZE, matrixOfDouble, i, TAG, MPI_COMM_WORLD, &stat)

I would like to know if (and how) it is possible on the slave side to
know that the received type is matrixOfDouble ?

If it is not possible, is there any other way in MPI ?
(I would like to avoid a extra master=> slave message to send the type).

Thanks
Sylvestre