/* Problem 3.6.3 in PPMPI
 *
 * by John Weatherwax (wax@alumn.mit.edu)
 *
 * To explore the MPI programming environment I changed
 * (with corresponding results):
 * 1) dest to 1 in all sending process (invoking an incorrect MPI_Recv)
 *    -Hangs waiting forever ... MPI_Recv never completes
 * 2) Incorrect string length (removed +1 from MPI_Send call)
 *    -Still worked...(removing more elements)
 *    -Prints until print process gets "\0"  (depends on contents of memory)
 * 3) Incorrect MPI data type in MPI_Send call
 *    -CHAR->INT: code crashed (larger data type)
 * 4) Incorrect recieve size (tried 10)
 *    -code crashed
 * 5) Incorrect MPI data type in recieve
 *    -CHAR->INT worked (change to DOUBLE)
 *    -worked these are larger data types
 * 6) Incorrect tag field in MPI recieve
 *    -program hangs
 *
 * 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 <stdio.h>
#include <string.h>
#include "mpi.h"

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  */
    MPI_Status  status;        /* return status for    */
                               /* receive              */

    /* Start up MPI */
    MPI_Init(&argc, &argv);

    /* Find out process rank  */
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

    /* Find out number of processes */
    MPI_Comm_size(MPI_COMM_WORLD, &p);

    if (my_rank != 0) {
        /* Create message */
        sprintf(message, "Greetings from process %d!",
            my_rank);
        dest = 0;
        /* Use strlen+1 so that '\0' gets transmitted */
        MPI_Send(message, strlen(message)+1, MPI_CHAR, 
            dest, tag, MPI_COMM_WORLD);
    } else { /* my_rank == 0 */
        for (source = 1; source < p; source++) {
            MPI_Recv(message, 100, MPI_CHAR, source, tag, 
                MPI_COMM_WORLD, &status);
            printf("%s\n", message);
        }
    }

    /* Shut down MPI */
    MPI_Finalize();
} /* main */