/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */
/*
 *  (C) 2003 by Argonne National Laboratory.
 *      See COPYRIGHT in top-level directory.
 */

/** PGROUP Creation (Connect/Accept Method)
  * James Dinan <dinan@mcs.anl.gov>
  * May, 2011
  *
  * In this test, processes create an intracommunicator and creation is
  * collective only on the members of the new communicator, not on the parent
  * communicator.  This is accomplished by building up and merging
  * intercommunicators using Connect/Accept to merge with a master/controller
  * process.
  */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#include <mpi.h>

const int verbose = 0;

void PGroup_create(int count, int members[], MPI_Comm * group);
void PGroup_create(int count, int members[], MPI_Comm * group)
{
    int i, me, nproc, is_member;
    char *port;
    MPI_Comm pgroup;

    MPI_Comm_rank(MPI_COMM_WORLD, &me);
    MPI_Comm_size(MPI_COMM_WORLD, &nproc);

    if (count == 0) {
        *group = MPI_COMM_NULL;
        return;
    }
    else if (count == 1 && members[0] == me) {
        *group = MPI_COMM_SELF;
        return;
    }

    for (i = 0, is_member = 0; i < count; i++) {
        if (members[i] == me) {
            is_member = 1;
            break;
        }
    }

    if (!is_member) {
        *group = MPI_COMM_NULL;
        return;
    }

    port = malloc(MPI_MAX_PORT_NAME);

    /* NOTE: Assume members list is identical and sorted on all processes */

    /* I am the leader */
    if (me == members[0]) {
        MPI_Comm pgroup_new;

        pgroup = MPI_COMM_SELF;

        MPI_Open_port(MPI_INFO_NULL, port);

        for (i = 1; i < count; i++) {
            MPI_Comm pgroup_old = pgroup;

            MPI_Send(port, MPI_MAX_PORT_NAME, MPI_CHAR, members[i], 0, MPI_COMM_WORLD);
            MPI_Comm_accept(port, MPI_INFO_NULL, 0, pgroup, &pgroup_new);
            MPI_Intercomm_merge(pgroup_new, 0 /* LOW */ , &pgroup);

            MPI_Comm_free(&pgroup_new);
            if (pgroup_old != MPI_COMM_SELF)
                MPI_Comm_free(&pgroup_old);
        }

        MPI_Close_port(port);
    }

    /* I am not the leader */
    else {
        int merged = 0;
        MPI_Comm pgroup_new;

        for (i = 0; i < count; i++) {
            if (members[i] == me) {
                MPI_Recv(port, MPI_MAX_PORT_NAME, MPI_CHAR, members[0], 0, MPI_COMM_WORLD,
                         MPI_STATUS_IGNORE);
                MPI_Comm_connect(port, MPI_INFO_NULL, 0, MPI_COMM_SELF, &pgroup_new);
                MPI_Intercomm_merge(pgroup_new, 1 /* HIGH */ , &pgroup);
                MPI_Comm_free(&pgroup_new);
                merged = 1;
            }
            else if (merged) {
                MPI_Comm pgroup_old = pgroup;

                MPI_Comm_connect(port, MPI_INFO_NULL, 0, pgroup, &pgroup_new);
                MPI_Intercomm_merge(pgroup_new, 0 /* HIGH */ , &pgroup);

                MPI_Comm_free(&pgroup_new);
                MPI_Comm_free(&pgroup_old);
            }
            /* else => !merged */
        }
    }

    free(port);
    *group = pgroup;
}


int main(int argc, char **argv)
{
    int me, nproc, i;
    int gsize, *glist;
    MPI_Comm group;

    MPI_Init(&argc, &argv);

    MPI_Comm_rank(MPI_COMM_WORLD, &me);
    MPI_Comm_size(MPI_COMM_WORLD, &nproc);

    gsize = nproc / 2 + (nproc % 2);
    glist = malloc(gsize * sizeof(int));

    for (i = 0; i < nproc; i += 2)
        glist[i / 2] = i;

    if (me % 2 == 0) {
        int gme, gnproc;

        PGroup_create(gsize, glist, &group);
        MPI_Barrier(group);

        MPI_Comm_rank(group, &gme);
        MPI_Comm_size(group, &gnproc);
        if (verbose)
            printf("[%d] Group rank = %d, size = %d\n", me, gme, gnproc);

        if (group != MPI_COMM_SELF)
            MPI_Comm_free(&group);
    }

    free(glist);

    MPI_Finalize();

    if (me == 0)
        printf(" No Errors\n");

    return 0;
}