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program basic
use mpi
use iso_fortran_env, only : REAL64
implicit none
integer, parameter :: size = 10000000
integer :: rc, myid, ntasks
integer :: message(size)
integer :: receiveBuffer(size)
integer :: status(MPI_STATUS_SIZE)
real(REAL64) :: t0, t1
call mpi_init(rc)
call mpi_comm_rank(MPI_COMM_WORLD, myid, rc)
call mpi_comm_size(MPI_COMM_WORLD, ntasks, rc)
message = myid
! Start measuring the time spent in communication
call mpi_barrier(mpi_comm_world, rc)
t0 = mpi_wtime()
! Send messages
if ( myid < ntasks-1 ) then
call mpi_send(message, size, MPI_INTEGER, myid+1, &
myid+1, MPI_COMM_WORLD, rc)
write(*,'(A10,I3,A20,I8,A,I3,A,I3)') 'Sender: ', myid, &
' Sent elements: ',size, &
'. Tag: ', myid+1, '. Receiver: ', myid+1
end if
! Receive messages
if ( myid > 0 ) then
call mpi_recv(receiveBuffer, size, MPI_INTEGER, myid-1, &
myid, MPI_COMM_WORLD, status, rc)
write(*,'(A10,I3,A,I3)') 'Receiver: ', myid, &
' First element: ', receiveBuffer(1)
end if
! Finalize measuring the time and print it out
t1 = mpi_wtime()
call mpi_barrier(mpi_comm_world, rc)
call flush(6)
if (myid == 0) then
write(*,*)
write(*,*) 'Timings:'
write(*, '(A20, I3, A, F6.3)') 'Time elapsed in rank', myid, ':', t1-t0
endif
call mpi_barrier(mpi_comm_world, rc)
call flush(6)
if (myid == ntasks - 1) then
write(*, '(A20, I3, A, F6.3)') 'Time elapsed in rank', myid, ':', t1-t0
endif
call mpi_finalize(rc)
end program basic