Deadlock with MPI_Isend

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  I have the following c/c++ code with Microsoft MPI
  
  #include <stdio.h>
  #include <stdlib.h>
  #include "mpi.h"
  int main (int argc, char *argv[])
   {
    int  err, numtasks, taskid;
    int out=0,val;
    MPI_Status status;
    MPI_Request req;
  
    err=MPI_Init(&argc, &argv);
    err=MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
    err=MPI_Comm_rank(MPI_COMM_WORLD, &taskid);
  
  
    int receiver=(taskid+1)% numtasks;
    int sender= (taskid-1+numtasks)% numtasks;
    printf("sender %d, receiver %d, rank %d\n",sender,receiver, taskid);
  
    val=50;   
    MPI_Isend(&val, 1, MPI_INT, receiver, 1, MPI_COMM_WORLD, &req);
    MPI_Irecv(&out, 1, MPI_INT, sender, 1, MPI_COMM_WORLD, &req);
    printf ("Rank: %d , Value: %d\n", taskid, out );
    err=MPI_Finalize();
    return 0;
   }

  The application goes in deadlock if launched with more than 2 processes. With 2 processes the application works but no write on "out" is performed. This code works with a linux mpi distribution, the problem seems to be only in the microsoft version. Any help ?
  

  Tuesday, January 26, 2016 4:47 PM