/* *************** 
   Ring Sum of Ranks, Sample for MPI calls
*/
#include <mpi.h>
#include <stdio.h>

struct {
 int myrank;
 double dmyrank;
} rankpak,rankpak1;

#define RESULT_PACKET_NBLOCKS 2
MPI_Datatype array_of_types[RESULT_PACKET_NBLOCKS]=
       {MPI_INT,MPI_DOUBLE};
int array_of_blocklenghts[RESULT_PACKET_NBLOCKS] =
       {1,1};
MPI_Aint array_of_displacements[RESULT_PACKET_NBLOCKS];

main(argc,argv)
int argc;
char **argv; 

{
  int myrankd;
  int size;
  int i,extent;
  int message,message1;
  MPI_Status status,status1;
  MPI_Request request;
  double start,end;


  int neighbor;
  int lsum=0;
  double dlsum=0;

  /* new datatype */
  MPI_Datatype newtype;

  /* init MPI */
  MPI_Init(&argc,&argv);
  MPI_Comm_rank(MPI_COMM_WORLD,&myrankd);
  MPI_Comm_size(MPI_COMM_WORLD,&size);

  MPI_Aint array_of_displacements[0]=0;
  MPI_Type_extent (MPI_INT, &extent);
  MPI_Aint array_of_displacements[1]=extent;
  MPI_Type_struct (2,
                array_of_blocklengths,
                array_of_displacements,
                array_of_types,
                &newtype);
  MPI_Type_commit (&newtype);

  /* message=myrank; */
  rankpak.myrank=myrankd;
  rankpak.dmyrank=myrankd;

  neighbor=(myrankd+1)%size;

  for(;;)

    {
   
      /* this call can be used to measure time */
      start=MPI_Wtime();
      /* non-blocking send */
      MPI_Isend(&rankpak,1,newtype,neighbor ,5,MPI_COMM_WORLD,&request);
      end=MPI_Wtime();  
      printf ("\n\rMessage send time:%f",end-start);


      MPI_Recv(&rankpak1,1,newtype, MPI_ANY_SOURCE, 5,MPI_COMM_WORLD,&status);

      /* wait for the message */
      MPI_Wait(&request, &status1);

      rankpak.myrank=rankpak1.myrank;
      rankpak.dmyrank=rankpak1.dmyrank;

      lsum+=rankpak.myrank;
      dlsum+=rankpak.dmyrank;

      /* break when the original message has come back */
      printf("\n\rLOCAL SUM:%d, %f",lsum,dlsum);
      if (rankpak1.myrank==myrankd) {
	printf("\n\rSUM:%d,%f",lsum,dlsum);
	break;
      }
    }
     
  printf("\n\r");
  MPI_Finalize();
  
}