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