! -*- f90 -*- ! ! Copyright (c) 2004-2006 The Trustees of Indiana University and Indiana ! University Research and Technology ! Corporation. All rights reserved. ! Copyright (c) 2006-2015 Cisco Systems, Inc. All rights reserved. ! Copyright (c) 2009-2012 Los Alamos National Security, LLC. ! All rights reserved. ! $COPYRIGHT$ ! ! Simple ring test program using the Fortran mpi_f08 module bindings. ! program ring use mpi_f08 implicit none integer :: rank, size, tag, next, from, i, message ! Start up MPI call MPI_INIT() call MPI_COMM_RANK(MPI_COMM_WORLD, rank) call MPI_COMM_SIZE(MPI_COMM_WORLD, size) ! 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 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) write(*, '("Process 0 sent to ", i2)') 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. i = 1 10 call MPI_Recv(message, i, MPI_INTEGER, from, tag, MPI_COMM_WORLD, & MPI_STATUS_IGNORE) 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) if (message .eq. 0) then write(*, '("Process ", i2, " exiting")') rank 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) endif ! All done call MPI_FINALIZE() end program