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C
C Copyright (c) 2004-2006 The Trustees of Indiana University and Indiana
C University Research and Technology
C Corporation. All rights reserved.
C Copyright (c) 2006 Cisco Systems, Inc. All rights reserved.
C
C Simple ring test program
C
program ring_f77
implicit none
include 'mpif.h'
integer rank, size, tag, next, from, message, ierr
C Start up MPI */
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, size, ierr)
C Calculate the rank of the next process in the ring. Use the
C modulus operator so that the last process "wraps around" to rank
C zero.
tag = 201
next = mod((rank + 1), size)
from = mod((rank + size - 1), size)
C If we are the "master" process (i.e., MPI_COMM_WORLD rank 0), put
C the number of times to go around the ring in the message.
if (rank .eq. 0) then
message = 10
print *, 'Process 0 sending ', message, ' to ', next, ' tag ',
& tag, ' (', size, ' processes in ring)'
call MPI_SEND(message, 1, MPI_INTEGER, next, tag,
& MPI_COMM_WORLD, ierr)
print *, 'Process 0 sent to ', next
endif
C Pass the message around the ring. The exit mechanism works as
C follows: the message (a positive integer) is passed around the
C ring. Each time it passes rank 0, it is decremented. When each
C processes receives a message containing a 0 value, it passes the
C message on to the next process and then quits. By passing the 0
C message first, every process gets the 0 message and can quit
C normally.
10 call MPI_RECV(message, 1, MPI_INTEGER, from, tag,
& MPI_COMM_WORLD, MPI_STATUS_IGNORE, ierr)
if (rank .eq. 0) then
message = message - 1
print *, 'Process 0 decremented value:', message
endif
call MPI_SEND(message, 1, MPI_INTEGER, next, tag,
& MPI_COMM_WORLD, ierr)
if (message .eq. 0) then
print *, 'Process ', rank, ' exiting'
goto 20
endif
goto 10
C The last process does one extra send to process 0, which needs to
C be received before the program can exit
20 if (rank .eq. 0) then
call MPI_RECV(message, 1, MPI_INTEGER, from, tag,
& MPI_COMM_WORLD, MPI_STATUS_IGNORE, ierr)
endif
C All done
call MPI_FINALIZE(ierr)
end
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