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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 in C.
*/
#include <stdio.h>
#include "mpi.h"
int main(int argc, char *argv[])
{
int rank, size, next, prev, message, tag = 201;
/* Start up MPI */
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
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. */
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;
printf("Process 0 sending %d to %d, tag %d (%d processes in ring)\n",
message, next, tag, size);
MPI_Send(&message, 1, MPI_INT, next, tag, MPI_COMM_WORLD);
printf("Process 0 sent to %d\n", next);
}
/* 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_Recv(&message, 1, MPI_INT, prev, tag, MPI_COMM_WORLD,
MPI_STATUS_IGNORE);
if (0 == rank) {
--message;
printf("Process 0 decremented value: %d\n", message);
}
MPI_Send(&message, 1, MPI_INT, next, tag, MPI_COMM_WORLD);
if (0 == message) {
printf("Process %d exiting\n", rank);
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_Recv(&message, 1, MPI_INT, prev, tag, MPI_COMM_WORLD,
MPI_STATUS_IGNORE);
}
/* All done */
MPI_Finalize();
return 0;
}