Question

EDIT #1:

so SOLUTION IS:

line

MPI_Gatherv(buffer, rank, MPI_INT, buffer, receive_counts, receive_displacements, MPI_INT, 0, MPI_COMM_WORLD);

has to be changed to

MPI_Gatherv(buffer, receive_counts[rank], MPI_INT, buffer, receive_counts, receive_displacements, MPI_INT, 0, MPI_COMM_WORLD);

thank you again for help

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ORIGINAL POST:

my code is from DeinoMPI

when I run mpiexec -localonly 4 skusamGatherv.exe, everithing is ok.

if I change line

int receive_counts[4] = { 0, 1, 2, 3 };

to

int receive_counts[4] = { 0, 1, 2, 1 };

compiling is still ok, but when i run mpiexec -localonly 4 skusamGatherv.exe I’ll get error

I thing it suppose to work

Thanks for help

---

I’ll get error:

Fatal error in MPI_Gatherv: Message truncated, error stack:
MPI_Gatherv(363)........................: MPI_Gatherv failed(sbuf=0012FF4C, scou
nt=0, MPI_INT, rbuf=0012FF2C, rcnts=0012FEF0, displs=0012FED8, MPI_INT, root=0,
MPI_COMM_WORLD) failed
MPIDI_CH3_PktHandler_EagerShortSend(351): Message from rank 3 and tag 4 truncate
d; 12 bytes received but buffer size is 4
unable to read the cmd header on the pmi context, Error = -1
.
0. [0][0][0][0][0][0] , [0][0][0][0][0][0]
Error posting readv, An existing connection was forcibly closed by the remote ho
st.(10054)
unable to read the cmd header on the pmi context, Error = -1
.
Error posting readv, An existing connection was forcibly closed by the remote ho
st.(10054)
1. [1][1][1][1][1][1] , [0][0][0][0][0][0]
unable to read the cmd header on the pmi context, Error = -1
.
Error posting readv, An existing connection was forcibly closed by the remote ho
st.(10054)
2. [2][2][2][2][2][2] , [0][0][0][0][0][0]
unable to read the cmd header on the pmi context, Error = -1
.
Error posting readv, An existing connection was forcibly closed by the remote ho
st.(10054)
3. [3][3][3][3][3][3] , [0][0][0][0][0][0]

job aborted:
rank: node: exit code[: error message]
0: jan-pc-nb: 1: Fatal error in MPI_Gatherv: Message truncated, error stack:
MPI_Gatherv(363)........................: MPI_Gatherv failed(sbuf=0012FF4C, scou
nt=0, MPI_INT, rbuf=0012FF2C, rcnts=0012FEF0, displs=0012FED8, MPI_INT, root=0,
MPI_COMM_WORLD) failed
MPIDI_CH3_PktHandler_EagerShortSend(351): Message from rank 3 and tag 4 truncate
d; 12 bytes received but buffer size is 4
1: jan-pc-nb: 1
2: jan-pc-nb: 1
3: jan-pc-nb: 1
Press any key to continue . . .

My code:

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

int main(int argc, char *argv[])
{
    int buffer[6];
    int rank, size, i;
    int receive_counts[4] = { 0, 1, 2, 3 };
    int receive_displacements[4] = { 0, 0, 1, 3 };

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    if (size != 4)
    {
        if (rank == 0)
        {
            printf("Please run with 4 processes\n");fflush(stdout);
        }
        MPI_Finalize();
        return 0;
    }
    for (i=0; i<rank; i++)
    {
        buffer[i] = rank;
    }
    MPI_Gatherv(buffer, rank, MPI_INT, buffer, receive_counts, receive_displacements, MPI_INT, 0, MPI_COMM_WORLD);
    if (rank == 0)
    {
        for (i=0; i<6; i++)
        {
            printf("[%d]", buffer[i]);
        }
        printf("\n");
        fflush(stdout);
    }
    MPI_Finalize();
    return 0;
}

Answer 1

Step back and consider what MPI_Gatherv is doing: it’s an MPI_Gather (in this case to rank 0) where each processor can send different amounts of data.

In your example, rank 0 sends 0 ints, rank 1 sends 1 int, rank 2 sends 2 ints, and rank 3 sends 3 ints.

MPIDI_CH3_PktHandler_EagerShortSend(351): Message from rank 3 and tag 4 truncated; 12 bytes received but buffer size is 4

it’s buried in a lot of other information, but it’s saying that rank 3 sent 3 ints (12 bytes) but rank 0 only had room for 1 int.

Look at the first three arguments to gatherv: ‘buffer, rank, MPI_INT’. No matter what you set receive to, rank 3 will always send 3 ints.

note that you can under-fill a buffer (you could have made the last item in receive_counts 100, say), but you told the MPI library with the smaller receive_counts[3] to only expect 1 int, even though you sent 3.