[OMPI users] Incorrect function call in simple C program

[Devon Hollowood]

Hello,

I am having trouble understanding why I am getting an error when running
the program produced by the attached C file. In this file, there are three
short functions: send(), bounce() and main(). send() and bounce() both use
MPI_Send() and MPI_Recv(), but critically, neither one is called from
main(), so as I understand it, neither function should ever be run. main()
is just:

int main(int argc, char *argv[]) {
>     int rank;
>
>     MPI_Init(&argc, &argv);
>     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
>
>     MPI_Finalize();
> }
>

Despite the fact that the program should never enter send() or bounce(),
when I compile with

mpicc mpi-issue.c -o mpi-issue
>

and run with

mpirun -n 2 --verbose ./mpi-issue
>

I get the following:

*** An error occurred in MPI_Send
> *** on a NULL communicator
> *** MPI_ERRORS_ARE_FATAL (processes in this communicator will now abort,
> ***    and potentially your MPI job)
> [dhcp-visitor-enr-117-111.slac.stanford.edu:99119] Local abort before
> MPI_INIT completed successfully; not able to aggregate error messages, and
> not able to guarantee that all other processes were killed!
> -------------------------------------------------------
> Primary job  terminated normally, but 1 process returned
> a non-zero exit code.. Per user-direction, the job has been aborted.
> -------------------------------------------------------
> --------------------------------------------------------------------------
> mpirun detected that one or more processes exited with non-zero status,
> thus causing
> the job to be terminated. The first process to do so was:
>
>   Process name: [[2829,1],0]
>   Exit code:    1
> --------------------------------------------------------------------------
>
>

How is it possible to be getting an error in MPI_Send(), if MPI_Send()
never gets run?

I am running open-mpi 1.10.2, installed via the Homebrew open-mpi package,
and this is running on my Macbook, which is running OSX Yosemite. I have
attached the results of ompi_info --all as ompi_info.txt.bz2

Any help would be appreciated! Sorry if this is a newb question and I am
missing something obvious--I tried my best to search for this issue but I
couldn't find anything.

-Devon

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


void send(int msg_len, int partner) {
    // initialize buffer
    unsigned char *buffer =
        (unsigned char *)malloc(msg_len * sizeof(unsigned char));
    for(int i = 0; i < msg_len; ++i) {
        buffer[i] = i % 256;
    }

    // time bounce
    double start_t = MPI_Wtime();
    MPI_Send(buffer, msg_len, MPI_UNSIGNED_CHAR, partner, msg_len,
            MPI_COMM_WORLD);
    MPI_Recv(buffer, msg_len, MPI_UNSIGNED_CHAR, partner, msg_len,
            MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    double end_t = MPI_Wtime();

    free(buffer);
    double time_taken = end_t - start_t;
    printf("%d: %e\n", msg_len, time_taken);
}

void bounce(int msg_len, int partner) {
    unsigned char *buffer = (unsigned char *) malloc(msg_len);
    MPI_Recv(buffer, msg_len, MPI_UNSIGNED_CHAR, partner, msg_len,
            MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    MPI_Send(buffer, msg_len, MPI_UNSIGNED_CHAR, partner, msg_len,
            MPI_COMM_WORLD);
    free(buffer);
}


int main(int argc, char *argv[]) {
    int rank;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    MPI_Finalize();
}

ompi_info.txt.bz2
Description: BZip2 compressed data