program main

!---Testing wether messages are buffered on the current platform.
!   (if messages are NOT buffered this program will deadlock)

      implicit none

!--Include the mpi header file
      include 'mpif.h'
      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=0.
       b=1.
      else
       a=1.
       b=0.
      end if

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

!--Finilize MPI
      call MPI_FINALIZE(irc)

      stop
      end