Thread: pthread programming question

Hi Guys,

I've got a multi process program as below. I'm using proc 0 as a passive receiver which used non-blocking receiver to receive messages sent from the other procs. However what I'm currently seeing is it can't receive from the last proc

for example if I called the program like this:

mpirun -np 4 test

the output I get is:

receive some into position 0
receive some into position 1
receive some into position 2
before waitsome
how many done:1
Msg (sbuf = 1) from 1 with tag 1
receive some second time into position 1
cnt:2
before waitsome
how many done:1
Msg (sbuf = 2) from 2 with tag 2
receive some second time into position 2
cnt:1
before waitsome

<<--------- from here the program just stalls waiting for the message from proc 3 to come


Any help on this would be must appreciated thanks

Code:

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

typedef struct {
   int answer;
   int read_size;
}REPLY;

int main(int argc, char *argv[])
{
    int rank, size, i, sbuf, cnt;

    MPI_Init( &argc, &argv );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    sbuf = rank;
    if (rank == 0) {
        MPI_Request* requests = (MPI_Request*)malloc((size-1)*sizeof(MPI_Request));
        MPI_Status* statuses = (MPI_Status*)malloc(sizeof(MPI_Status)*(size-1));
        int* indices = (int *)malloc((size-1)*sizeof(int));
        int* buf = (int *)malloc((size-1)*sizeof(int));

        int j, ndone;

        cnt = size-1;
        for (i=0; i<size-1; i++) {
            printf("receive some into position %d\n",i);
            MPI_Irecv(buf+i, 1, MPI_INT, i, MPI_ANY_TAG, MPI_COMM_WORLD, &requests[i]);
        }
        while(cnt > 0) {
            printf("before waitsome\n");
            MPI_Waitsome(size-1, requests, &ndone, indices, statuses);
            printf("how many done:%d\n",ndone);
            for (i=0; i<ndone; i++) {
                j = indices[i];
                printf("Msg (sbuf = %d) from %d with tag %d\n",
                        buf[j],
                        statuses[i].MPI_SOURCE,
                        statuses[i].MPI_TAG);
                printf("receive some second time into position %d\n",j);
                MPI_Irecv(buf+j, 1, MPI_INT, j, MPI_ANY_TAG, MPI_COMM_WORLD, &requests[j]);
            }
            cnt -= ndone;
            printf("cnt:%d\n",cnt);
        }
    }
    else {
        printf("proc %d sending...\n",rank);
        MPI_Send( &sbuf, 1, MPI_INT, 0, rank, MPI_COMM_WORLD);
    }
    MPI_Finalize();
    return 0;
}