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