program main

!---Testing wether messages are buffered on the current platform.
!   (if messages are NOT buffered this program will deadlock)
      use mpi
      implicit none

!--Include the mpi header file
      integer ierr,myid,numprocs
      integer irc,tag1,tag2
      integer status(MPI_STATUS_SIZE)
      real a,b

!--Initialize MPI
      call MPI_INIT( ierr )

!--Who am I? --- get my rank=myid
      call MPI_COMM_RANK( MPI_COMM_WORLD, myid, ierr )

!--How many processes in the global group?
      call MPI_COMM_SIZE( MPI_COMM_WORLD, numprocs, ierr )
      print *, "Process ", myid, " of ", numprocs, " is alive"

      if (myid == 0) then
       a=90.
       b=1.
       write(*,*)'part 1: myid=',myid,' a=',a,' b=',b
      else
       a=4. *myid
       b=7. *myid
       write(*,*)'part 1: myid=',myid,' a=',a,' b=',b
      end if

!--Exchange messages
      tag1=1
      tag2=2
      if (myid == 0) then
       call mpi_sendrecv(a,1,mpi_real,1,tag1,   &  !send a, get b.
                         b,1,mpi_real,2,tag2,   &
                         MPI_COMM_WORLD, status,ierr)
      !elseif (myid == 1) then
      ! call mpi_sendrecv(b,1,mpi_real,0,tag2,   &   !send b, get a
      !                   a,1,mpi_real,0,tag1,   &
      !                   MPI_COMM_WORLD,status,ierr)

     elseif (myid==1) then
           call mpi_recv(a,1,mpi_real,0,tag1, MPI_COMM_WORLD, status, ierr)
     elseif (myid==2) then
           call mpi_send(b,1,mpi_real,0,tag2,MPI_COMM_WORLD, ierr)
      end if

       write(*,*)'part2: myid=',myid,' a=',a,' b=',b
!--Finilize MPI
      call MPI_FINALIZE(irc)

      stop
      end