DEADLOCK: attempting to send a message to the local process without a prior matching receive

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  Hi,

  I am new to MPI programming and still trying out very basic codes.

  I wanted to make core 0 to receive simple values sent by other workers.  But it gives me a MPI error at run time. when executing MPI_Send command.

  Here is my code,

  #include <stdio.h>
  #include <mpi.h>
  
  #include<iostream>
  
  using namespace std;
  
  int main(int argc, char *argv[]) {
  int numprocs, rank, namelen, ierr;
  char processor_name[MPI_MAX_PROCESSOR_NAME];
  MPI_Init(&argc, &argv); // What ever I write in between will be parallelize.,....................
  MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank); // Current Worker index
  MPI_Get_processor_name(processor_name, &namelen);

      // Send rank to process 0
  
          double val = -1.0*rank;
          MPI_Send(&val, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
          printf("ProcID %d sent value %f to ProcID %d",rank,val,0);
    
  
  
      if(rank == 0){
  
         int i;
         double val, sum = 0;
          MPI_Status status;
  
          int cp = 0;
  
          for (i = 0 ; i!=numprocs ; ++i){
              ierr = MPI_Recv(&val, 1, MPI_DOUBLE, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status);
  
              if(ierr == MPI_SUCCESS){
                  printf("ProcID %d Receives value %f from ProcID %d\n",rank,val);
                  sum += 1;
                  cp++;
               }
               else MPI_Abort(MPI_COMM_WORLD,1);
  
          }
          printf("the Total is %f\n",sum);
      }
  
  MPI_Finalize();//.......................................................................
  }
  

  When I change MPI_Send line to,

  if(rank != 0) {
          double val = -1.0*rank;
          MPI_Send(&val, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
          printf("ProcID %d sent value %f to ProcID %d",rank,val,0);
      }

  I don't get any thing at all. It doesn't do anything.

  I am running this on my laptop with a core i7 processor. 

  Any help would be appreciated?

  Thursday, August 4, 2016 5:38 PM

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