DeinoMPI

The Great and Terrible implementation of MPI-2

MPI_Comm_remote_size

Determines the size of the remote group associated with an inter-communictor

int MPI_Comm_remote_size(
  MPI_Comm comm,
  int *size
);

Parameters

comm: [in] communicator (handle)
size: [out] number of processes in the remote group of comm (integer)

Thread and Interrupt Safety

This routine is both thread- and interrupt-safe. This means that this routine may safely be used by multiple threads and from within a signal handler.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierris an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGERin Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS: No error; MPI routine completed successfully.

MPI_ERR_COMM: Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

MPI_ERR_ARG: Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

Example Code

The following sample code illustrates MPI_Comm_remote_size.

#include <stdio.h>
#include "mpi.h"

#define BUFSIZE 2000

int main( int argc, char *argv[] )
{
    MPI_Status status;
    MPI_Comm comm,scomm;
    int a[10], b[10];
    int buf[BUFSIZE], *bptr, bl, i, j, rank, size, color, errs=0;

    MPI_Init( 0, 0 );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    color = rank % 2;
    MPI_Comm_split( MPI_COMM_WORLD, color, rank, &scomm );
    MPI_Intercomm_create( scomm, 0, MPI_COMM_WORLD, 1-color, 52, &comm);
    MPI_Comm_rank( comm, &rank );
    MPI_Comm_remote_size( comm, &size );
    MPI_Buffer_attach( buf, BUFSIZE );

    for (j=0; j<10; j++) {
        for (i=0; i<10; i++) {
            a[i] = (rank + 10 * j) * size + i;
        }
        MPI_Bsend( a, 10, MPI_INT, 0, 27+j, comm );
    }
    if (rank == 0) {
        for (i=0; i<size; i++) {
            for (j=0; j<10; j++) {
                int k;
                status.MPI_TAG = -10;
                status.MPI_SOURCE = -20;
                MPI_Recv( b, 10, MPI_INT, i, 27+j, comm, &status );

                if (status.MPI_TAG != 27+j) {
                    errs++;
                    printf( "Wrong tag = %d\n", status.MPI_TAG );fflush(stdout);
                }
                if (status.MPI_SOURCE != i) {
                    errs++;
                    printf( "Wrong source = %d\n", status.MPI_SOURCE );fflush(stdout);
                }
                for (k=0; k<10; k++) {
                    if (b[k] != (i + 10 * j) * size + k) {
                        errs++;
                        printf( "received b[%d] = %d from %d tag %d\n", k, b[k], i, 27+j );fflush(stdout);
                    }
                }
            }
        }
    }
    MPI_Buffer_detach( &bptr, &bl );
    MPI_Comm_free(&scomm);
    MPI_Comm_free(&comm);
    MPI_Finalize();
    return errs;
}

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