/* recipMPI.c - MPI version of master0/slave0.c in PVM
 * calculate the reciprocal
 * variation of greetings.c -- greetings program
 *
 * Send a message from all processes with rank != 0 to process 0.
 *    Process 0 prints the messages received.
 *
 * Input: none.
 * Output: contents of messages received by process 0.
 *
 * See Chapter 3, pp. 41 & ff in PPMPI.
 */
#include <iostream>
#include <string.h>
#include <stdio.h>
#include "mpi.h"
using namespace std;

int main(int argc, char* argv[]) {
    int         my_rank;       /* rank of process      */
    int         p;             /* number of processes  */
    int         source;        /* rank of sender       */
    int         dest;          /* rank of receiver     */
    int         tag = 0;       /* tag for messages     */
    char        message[100];  /* storage for message  */
    double      reciprocal;
    int num;
    char        name[100];     // Processor name
    int         len;           // Length of the name
    double      start_time, 
                end_time;    
    MPI::Status  status;        /* return status for    */
                               /* receive              */

    /* Start up MPI */
    MPI::Init(argc, argv);

    /* Find out process rank  */
    my_rank = MPI::COMM_WORLD.Get_rank();

    /* Find out number of processes */
    p = MPI::COMM_WORLD.Get_size();
    
    MPI_Get_processor_name(name, &len);

    if (my_rank != 0) {
         source = 0; //receive from the "master process"
         MPI::COMM_WORLD.Recv(&num, 1, MPI_INT, source, tag, status);
        if (num==0)
            {reciprocal = 0.0;}
        else
            {reciprocal = 1.0 / num;}
	    
        /* Create message */
        sprintf(message, "Greetings from process %d!",
            my_rank);
        dest = 0;
	MPI::COMM_WORLD.Send(&reciprocal, 1, MPI_DOUBLE,dest, tag);
        /* Use strlen+1 so that '\0' gets transmitted */
        MPI::COMM_WORLD.Send(message, strlen(message)+1, MPI_CHAR, 
            dest, tag);
	MPI::COMM_WORLD.Send(name, len+1, MPI_CHAR, 
            dest, tag);
    } else { /* my_rank == 0 */
        start_time = MPI_Wtime();
        cout << "Hello from process 0 on " << name << endl;
        for (source = 1; source < p; source++) {
	    num = source;
	    dest = source;
	    MPI::COMM_WORLD.Send(&num, 1, MPI_INT,dest, tag);
	    MPI::COMM_WORLD.Recv(&reciprocal, 1, MPI_DOUBLE, source, tag, status);
            MPI::COMM_WORLD.Recv(message, 100, MPI_CHAR, source, tag, status);
	    MPI::COMM_WORLD.Recv(name, 100, MPI_CHAR, source, tag, status);
            cout << message << " on machine " << name 
	         << " reciprocal = " << reciprocal << endl;
        }
	end_time = MPI_Wtime();
	cout << "Total time for sending/recieving data: " 
	     << (end_time - start_time) << endl;
    }

    /* Shut down MPI */
    MPI::Finalize();
} /* main */

/*
lamboot -v lamhosts

mpiCC -o recipMPICC recipMPI.cpp

mpirun -np 10 recipMPICC
Hello from process 0 on slingshot
Greetings from process 1! on machine slingshot reciprocal = 1
Greetings from process 2! on machine slingshot reciprocal = 0.5
Greetings from process 3! on machine slingshot reciprocal = 0.333333
Greetings from process 4! on machine slingshot reciprocal = 0.25
Greetings from process 5! on machine slingshot reciprocal = 0.2
Greetings from process 6! on machine slingshot reciprocal = 0.166667
Greetings from process 7! on machine slingshot reciprocal = 0.142857
Greetings from process 8! on machine slingshot reciprocal = 0.125
Greetings from process 9! on machine slingshot reciprocal = 0.111111
Total time for sending/recieving data: 0.0826579

*/