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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
integer :: source, destination
call mpi_init(rc)
call mpi_comm_rank(MPI_COMM_WORLD, myid, rc)
call mpi_comm_size(MPI_COMM_WORLD, ntasks, rc)
message = myid
! Set source and destination ranks
if (myid < ntasks-1) then
destination = myid + 1
else
destination = MPI_PROC_NULL
end if
if (myid > 0) then
source = myid - 1
else
source = MPI_PROC_NULL
end if
! Start measuring the time spent in communication
call mpi_barrier(mpi_comm_world, rc)
t0 = mpi_wtime()
! Send and receive messages
call mpi_sendrecv(message, size, MPI_INTEGER, destination, myid + 1, &
receiveBuffer, size, MPI_INTEGER, source, MPI_ANY_TAG, &
MPI_COMM_WORLD, status, rc)
write(*,'(A10,I3,A20,I8,A,I3,A,I3)') 'Sender: ', myid, &
' Sent elements: ', size, &
'. Tag: ', myid + 1, &
'. Receiver: ', destination
! 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