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//
// 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
//
#include "mpi.h"
#include <iostream>
int main(int argc, char *argv[])
{
int rank, size, next, prev, message, tag = 201;
// Start up MPI
MPI::Init();
rank = MPI::COMM_WORLD.Get_rank();
size = MPI::COMM_WORLD.Get_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.
next = (rank + 1) % size;
prev = (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 (0 == rank) {
message = 10;
std::cout << "Process 0 sending " << message << " to " << next
<< ", tag " << tag << " (" << size << " processes in ring)"
<< std::endl;
MPI::COMM_WORLD.Send(&message, 1, MPI::INT, next, tag);
std::cout << "Process 0 sent to " << next << std::endl;
}
// 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.
while (1) {
MPI::COMM_WORLD.Recv(&message, 1, MPI::INT, prev, tag);
if (0 == rank) {
--message;
std::cout << "Process 0 decremented value: " << message
<< std::endl;
}
MPI::COMM_WORLD.Send(&message, 1, MPI::INT, next, tag);
if (0 == message) {
std::cout << "Process " << rank << " exiting" << std::endl;
break;
}
}
// The last process does one extra send to process 0, which needs
// to be received before the program can exit */
if (0 == rank) {
MPI::COMM_WORLD.Recv(&message, 1, MPI::INT, prev, tag);
}
// All done
MPI::Finalize();
return 0;
}
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