include "mpiSim.f90"
PROGRAM simple_deadlock
include "useSim.f90"
! INCLUDE 'mpif.h'
!
! This example is from:
! "Introduction to MPI" – created by the PACS Training Group

! Note that mpiSim does not detect deadlock occurring in this example.
! This code does in fact deadlock when run with a real MPI library.
! The correct code for this example is: nodeadlock_ex.f90
!
INTEGER myrank, ierr, status(MPI_STATUS_SIZE)
REAL a(100), b(100)
a=3
b=4
! Initialize MPI:
call MPI_INIT(ierr)
! Get my rank:
call MPI_COMM_RANK(MPI_COMM_WORLD, myrank, ierr)

! "Deadlock occurs when 2 (or more) processes are blocked and each is
! waiting for the other to make progress. Neither process makes
! progress because each depends on the other to make progress first."
! Process 1 receives and sends; same for process 1
if( myrank.eq.0 )then
  call MPI_RECV( b, 100, MPI_REAL, 1, 19, MPI_COMM_WORLD, status, ierr )
  call MPI_SEND( a, 100, MPI_REAL, 1, 17, MPI_COMM_WORLD, ierr)
else if ( myrank.eq.1 )then
  call MPI_RECV( b, 100, MPI_REAL, 0, 17, MPI_COMM_WORLD, status, ierr )
  call MPI_SEND( a, 100, MPI_REAL, 0, 19, MPI_COMM_WORLD, ierr)
endif
! Wrap Up.
 call MPI_FINALIZE(ierr)
 write(*,*) "Simple deadlock example all done."

 end program simple_deadlock