nonblock.c

#include<stdio.h>
#include<mpi.h>
int main( int argc, char *argv[]){
     int numTasks, rank,    rc0, rc1, rc2, rc3;
    MPI_Request request[4];
    MPI_Status status[4];
                
     char sendChar;
     char receiveChar;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numTasks); //get from -np    
    MPI_Comm_rank(MPI_COMM_WORLD, &rank); //each process's ID
                
   if(rank == 0){    
      sendChar = 'A';
                 int count = 1;
       int destRank = 1;
       int sourceRank = 1; //MPI_ANY_SOURCE    
       int tagSendMSGID = 6;
       int tagRecvMSGID = 9;
    
      rc0 = MPI_Isend(&sendChar, count, MPI_CHAR,    
                    destRank, tagSendMSGID, MPI_COMM_WORLD, &request[0]);    
      rc1 = MPI_Irecv(&receiveChar, count, MPI_CHAR,    
                      sourceRank, tagRecvMSGID, MPI_COMM_WORLD, &request[1]);
  } else if(rank == 1){
      sendChar = 'Z';
       int count = 1;
       int destRank = 0;    
       int sourceRank = 0;
       int tagRecvMSGID = 6;
       int tagSendMSGID = 9;

      rc2 = MPI_Isend(&sendChar, count, MPI_CHAR,    
        destRank, tagSendMSGID, MPI_COMM_WORLD, &request[2]);
      rc3 =    MPI_Irecv(&receiveChar, count, MPI_CHAR,    
        sourceRank, tagRecvMSGID, MPI_COMM_WORLD, &request[3]);
  }
                
     //MPI_Waitall(4, request, status);
    printf( "Rank = %d, received char = %c, send char = %c\n",    
      rank, receiveChar, sendChar);
                
    printf( "rc0 = %d, rc1 = %d, rc2 = %d, rc3 = %d\n", rc0, rc1, rc2, rc3);
    
    MPI_Finalize();
     return 0;
}