/* 
 * The root node sends out a message to the next node in the ring and each node then passes the 
 * message along to the next node.  The root node times how long it takes for the message to get back to it.
 */

#include<stdio.h>      /* for input/output       */
#include<mpi.h>        /* for mpi routines       */

#define BUFSIZE 64     /* The size of the messege being passed */

main( int argc, char** argv)
{
	double start,finish;
	int my_rank;                     /* the rank of this process       */
	int n_processes;                 /* the total number of processes  */
	char buf[BUFSIZE];               /* a buffer for the messege       */
	int tag=0;                       /* not important here             */
	MPI_Status status;               /* not important here             */

	MPI_Init(&argc, &argv);                      /* Initializing mpi       */

	MPI_Comm_size(MPI_COMM_WORLD, &n_processes); /* Getting # of processes */

	MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);     /* Getting my rank        */

	/* 
	* If this process is the root process send a messege to the next node
	* and wait to recieve one from the last node.  Time how long it takes
	* for the messege to get around the ring.  If this process is not the 
	* root node, wait to recieve a messege from the previous node and
	* then send it to the next node.
	*/

	start=MPI_Wtime();
	printf("Hello world! I am %d of %d\n", my_rank, n_processes);
	if( my_rank == 0 )
	{ 
		/* send to the next node */

		MPI_Send(buf, BUFSIZE, MPI_CHAR, my_rank+1, tag,
		MPI_COMM_WORLD);

		/* recieve from the last node */

		MPI_Recv(buf, BUFSIZE, MPI_CHAR, n_processes-1, tag,
		MPI_COMM_WORLD, &status);
	}
	if( my_rank != 0)
	{
		/* recieve from the previous node */

		MPI_Recv(buf, BUFSIZE, MPI_CHAR, my_rank-1, tag,
		MPI_COMM_WORLD, &status);

		/* send to the next node */

		MPI_Send(buf, BUFSIZE, MPI_CHAR, (my_rank+1)%n_processes, tag,
		MPI_COMM_WORLD);
	}
	finish=MPI_Wtime();

	MPI_Finalize(); /* I'm done with mpi stuff */

	/* Print out the results. */

	if (my_rank == 0)
	{
		printf("Total time used was %f seconds\n", finish-start);
	}

	return 0;
}