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) 2006-2012 Cisco Systems, Inc. All rights reserved. C $COPYRIGHT$ 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 write(*, '("Process 0 sending ", i2, " to ", i2, " tag ", & i3, " (", i2, " processes in ring)")') & message, next, tag, size call MPI_SEND(message, 1, MPI_INTEGER, next, tag, & MPI_COMM_WORLD, ierr) write(*, '("Process 0 sent to ", i2)') & 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 write(*, '("Process 0 decremented value: ", i2)') message endif call MPI_SEND(message, 1, MPI_INTEGER, next, tag, & MPI_COMM_WORLD, ierr) if (message .eq. 0) then write(*, '("Process ", i2, " exiting")') rank 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