Newer
Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
program chain
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,2)
real(REAL64) :: t0, t1
integer :: source, destination
integer :: count
integer :: requests(2)
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()
! Receive messages in the back ground
call mpi_irecv(receiveBuffer, size, MPI_INTEGER, source, &
MPI_ANY_TAG, MPI_COMM_WORLD, requests(1), rc)
! Send messages in the back ground
call mpi_isend(message, size, MPI_INTEGER, destination, &
myid + 1, MPI_COMM_WORLD, requests(2), rc)
! Blocking wait for messages
call mpi_waitall(2, requests, status, rc)
! Use status parameter to find out the no. of elements received
call mpi_get_count(status(:,1), MPI_INTEGER, count, rc)
write(*,'(A10,I3,A20,I8,A,I3,A,I3)') 'Sender: ', myid, &
' Sent elements: ', size, &
'. Tag: ', myid + 1, &
'. Receiver: ', destination
write(*,'(A10,I3,A20,I8,A,I3,A,I3)') 'Receiver: ', myid, &
'received elements: ', count, &
'. Tag: ', status(MPI_TAG, 1), &
'. Sender: ', status(MPI_SOURCE, 1)
! 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 chain