! ! Copyright (c) 2004-2006 The Trustees of Indiana University and Indiana ! University Research and Technology ! Corporation. All rights reserved. ! Copyright (c) 2006 Cisco Systems, Inc. All rights reserved. ! ! Simple ring test program ! program ring use mpi implicit none integer :: rank, size, tag, next, from, message, ierr ! 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) ! Calculate the rank of the next process in the ring. Use the modulus ! operator so that the last process "wraps around" to rank zero. tag = 201 next = mod((rank + 1), size) from = mod((rank + size - 1), size) ! If we are the "master" process (i.e., MPI_COMM_WORLD rank 0), put ! 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 ! Pass the message around the ring. The exit mechanism works as ! follows: the message (a positive integer) is passed around the ring. ! Each time it passes rank 0, it is decremented. When each processes ! receives a message containing a 0 value, it passes the message on to ! the next process and then quits. By passing the 0 message first, ! every process gets the 0 message and can quit 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 ! The last process does one extra send to process 0, which needs to 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 ! All done call MPI_FINALIZE(ierr) end program