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#ifndef _RHEO_MPI_SCATTER_INIT_H
#define _RHEO_MPI_SCATTER_INIT_H
///
/// This file is part of Rheolef.
///
/// Copyright (C) 2000-2009 Pierre Saramito <Pierre.Saramito@imag.fr>
///
/// Rheolef is free software; you can redistribute it and/or modify
/// it under the terms of the GNU General Public License as published by
/// the Free Software Foundation; either version 2 of the License, or
/// (at your option) any later version.
///
/// Rheolef is distributed in the hope that it will be useful,
/// but WITHOUT ANY WARRANTY; without even the implied warranty of
/// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
/// GNU General Public License for more details.
///
/// You should have received a copy of the GNU General Public License
/// along with Rheolef; if not, write to the Free Software
/// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
/// 
/// =========================================================================

#include "rheolef/compiler.h"
#include "rheolef/distributed.h"
#include "rheolef/scatter_message.h"

#include "rheolef/msg_sort_with_permutation.h"
#include "rheolef/msg_to_context.h"
#include "rheolef/msg_from_context_pattern.h"
#include "rheolef/msg_from_context_indices.h"
#include "rheolef/msg_local_context.h"
#include "rheolef/msg_local_optimize.h"

#include "rheolef/msg_util.h"
#include <boost/functional.hpp>
#include <boost/iterator/transform_iterator.hpp>

/*F:
NAME: mpi_scatter_init -- gather/scatter initialize (@PACKAGE@ @VERSION@)
DESCRIPTION:
  Initialize communication
  for distributed to sequential scatter context.
COMPLEXITY:
  Time and memory complexity is O(nidx+nproc).
  For finite-element problems in d dimenion

|   nidx ~ N^((d-1)/d)

  where N is the number of degrees of freedom.

IMPLEMENTATION
  Inspirated from petsc-2.0/vpscat.c: VecScatterCreate_PtoS()
AUTHORS:
    LMC-IMAG, 38041 Grenoble cedex 9, France
    | Pierre.Saramito@imag.fr
DATE:   23 march 1999
END:
*/

namespace rheolef {

//<mpi_scatter_init:
template <class Message, class Size, class SizeRandomIterator1,
          class SizeRandomIterator2, class SizeRandomIterator3, class Tag>
void
mpi_scatter_init (
// input:
    Size                nidx,
    SizeRandomIterator1 idx,
    Size                nidy,
    SizeRandomIterator2 idy,
    Size                idy_maxval,
    SizeRandomIterator3 ownership,
    Tag                 tag,
    const distributor::communicator_type& comm,
// output:
    Message&    from,
    Message&    to)
{
    typedef Size size_type;
    size_type  my_proc = comm.rank();
    size_type  nproc   = comm.size();
 
    // ------------------------------------------------------- 
    // 1) first count number of contributors to each processor
    // ------------------------------------------------------- 
    std::vector<size_type> msg_size(nproc, 0);
    std::vector<size_type> msg_mark(nproc, 0);
    std::vector<size_type> owner   (nidx);
    size_type send_nproc = 0;
    {
      size_type iproc = 0;
      for (size_type i = 0; i < nidx; i++) {
        for (; iproc < nproc; iproc++) {
          if (idx[i] >= ownership[iproc] && idx[i] < ownership[iproc+1]) {
	    owner[i] = iproc;
            msg_size [iproc]++;
            if (!msg_mark[iproc]) {
               msg_mark[iproc] = 1;
               send_nproc++;
            }
            break;
          }
        }
        check_macro (iproc != nproc, "bad stash data: idx["<<i<<"]="<<idx[i]<<" out of range [0:"<<ownership[nproc]<<"[");
      }
    } // end block
    // ------------------------------------------------------- 
    // 2) avoid to send message to my-proc in counting
    // ------------------------------------------------------- 
    size_type n_local  = msg_size[my_proc]; 
    if (n_local != 0) {
        msg_size [my_proc] = 0;
        msg_mark [my_proc] = 0;
        send_nproc--;
    }
    // ----------------------------------------------------------------
    // 3) compute number of messages to be send to my_proc
    // ----------------------------------------------------------------
    std::vector<size_type> work(nproc);
    mpi::all_reduce (
	comm, 
        msg_mark.begin().operator->(),
	nproc,
	work.begin().operator->(),
	std::plus<size_type>());
    size_type receive_nproc = work [my_proc];
    // ----------------------------------------------------------------
    // 4) compute messages max size to be send to my_proc
    // ----------------------------------------------------------------
    mpi::all_reduce (
        comm,
        msg_size.begin().operator->(),
        nproc,
	work.begin().operator->(),
        mpi::maximum<size_type>());
    size_type receive_max_size = work [my_proc];
    // ----------------------------------------------------------------
    // 5) post receive: exchange the buffer adresses between processes
    // ----------------------------------------------------------------
    std::list<std::pair<size_type,mpi::request> >   receive_waits;
    std::vector<size_type>                          receive_data (receive_nproc*receive_max_size);
    for (size_type i_receive = 0; i_receive < receive_nproc; i_receive++) {
      mpi::request i_req = comm.irecv (
	  mpi::any_source,
	  tag,
          receive_data.begin().operator->() + i_receive*receive_max_size,
	  receive_max_size);
      receive_waits.push_back (std::make_pair(i_receive, i_req));
    }
    // ---------------------------------------------------------------------------
    // 6) compute the send indexes
    // ---------------------------------------------------------------------------
    // comme idx est trie, on peut faire une copie de idx dans send_data
    // et du coup owner et send_data_ownership sont inutiles
    std::vector<size_type> send_data (nidx);
    std::copy (idx, idx+nidx, send_data.begin());
    // ---------------------------------------------------------------------------
    // 7) do send
    // ---------------------------------------------------------------------------
    std::list<std::pair<size_type,mpi::request> > send_waits;
    {
      size_type i_send = 0;
      size_type i_start = 0;
      for (size_type iproc = 0; iproc < nproc; iproc++) {
        size_type i_msg_size = msg_size[iproc];
        if (i_msg_size == 0) continue;
        mpi::request i_req = comm.isend (
	    iproc,
	    tag, 
            send_data.begin().operator->() + i_start,  
            i_msg_size);
        send_waits.push_back(std::make_pair(i_send,i_req));
        i_send++;
        i_start += i_msg_size;
      }
    } // end block
    // ---------------------------------------------------------------------------
    // 8) wait on receives
    // ---------------------------------------------------------------------------
    // note: for wait_all, build an iterator adapter that scan the pair.second in [index,request]
    // and then get an iterator in the pair using iter.base(): retrive the corresponding index
    // for computing the position in the receive.data buffer
    typedef boost::transform_iterator<select2nd<size_t,mpi::request>, std::list<std::pair<size_t,mpi::request> >::iterator>
            request_iterator;
    std::vector<size_type> receive_size (receive_nproc);
    std::vector<size_type> receive_proc (receive_nproc);
    size_type receive_total_size = 0;
    while (receive_waits.size() != 0) {
        typedef size_type data_type; // exchanged data is of "size_type" 
        request_iterator iter_r_waits (receive_waits.begin(), select2nd<size_t,mpi::request>()),
                         last_r_waits (receive_waits.end(),   select2nd<size_t,mpi::request>());
	// waits on any receive...
        std::pair<mpi::status,request_iterator> pair_status = mpi::wait_any (iter_r_waits, last_r_waits);
	// check status
	boost::optional<int> i_msg_size_opt = pair_status.first.count<data_type>();
	check_macro (i_msg_size_opt, "receive wait failed");
    	int iproc = pair_status.first.source();
	check_macro (iproc >= 0, "receive: source iproc = "<<iproc<<" < 0 !");
	// get size of receive and number in data
	size_type i_msg_size = (size_t)i_msg_size_opt.get();
        std::list<std::pair<size_t,mpi::request> >::iterator i_pair_ptr = pair_status.second.base();
        size_type i_receive = (*i_pair_ptr).first;
        receive_proc [i_receive] = iproc;
        receive_size [i_receive] = i_msg_size;
        receive_total_size += i_msg_size;
        receive_waits.erase (i_pair_ptr);
    }
    // ---------------------------------------------------------------------------
    // 9) allocate the entire send(to) scatter context
    // ---------------------------------------------------------------------------
    to.resize (receive_total_size, receive_nproc);

    // ---------------------------------------------------------------------------
    // 10) compute the permutation of values that gives the sorted source[] sequence
    // ---------------------------------------------------------------------------
    // init: perm[i] = i
    std::vector<size_type> perm(receive_nproc);
    copy(index_iterator<size_type>(), index_iterator<size_type>(receive_nproc), perm.begin());
    sort_with_permutation (
        receive_proc.begin().operator->(),
        perm.begin().operator->(),
        receive_nproc);
    // ---------------------------------------------------------------------------
    // 11) Computes the receive compresed message pattern for send(to)
    // ---------------------------------------------------------------------------
    size_type istart = ownership[my_proc]; // = ownership.first_index()
    msg_to_context (
        perm.begin(),
        perm.end(),
        receive_proc.begin(),
        receive_size.begin(),
        receive_data.begin(),
        receive_max_size,
        istart,
        to.procs().begin(),
        to.starts().begin(),
        to.indices().begin());
    // ---------------------------------------------------------------------------
    // 12) allocate the entire receive(from) scatter context
    // ---------------------------------------------------------------------------
    from.resize(nidy, send_nproc);
    // ---------------------------------------------------------------------------
    // 13) Computes the receive compresed message pattern for receive(from)
    // ---------------------------------------------------------------------------
    std::vector<size_type> proc2from_proc(nproc);
    msg_from_context_pattern (
        msg_size.begin(),
        msg_size.end(),
        from.procs().begin(),
        from.starts().begin(),
        proc2from_proc.begin());
    // ---------------------------------------------------------------------------
    // 14) Computes the receive compresed message indices for receive(from)
    // ---------------------------------------------------------------------------
    // assume that indices are sorted by increasing order
    std::vector<size_type> start(send_nproc+1);
    copy (from.starts().begin(), from.starts().end(), start.begin());
    msg_from_context_indices (
        owner.begin(),
        owner.end(),
        idy,
        proc2from_proc.begin(),
        my_proc,
        idy_maxval,
        start.begin(),
        from.indices().begin());
    // ---------------------------------------------------------------------------
    // 15) wait on sends
    // ---------------------------------------------------------------------------
    request_iterator iter_s_waits (send_waits.begin(), select2nd<size_type,mpi::request>()),
                     last_s_waits (send_waits.end(),   select2nd<size_type,mpi::request>());
    mpi::wait_all (iter_s_waits, last_s_waits);
    // ---------------------------------------------------------------------------
    // 16) Computes the receive compresed message local pattern,
    // i.e. the only part that does not requires communication.
    // ---------------------------------------------------------------------------
    from.local_slots.resize(n_local);
    to.local_slots.resize(n_local);
    size_type ilast = ownership[my_proc+1]; // = ownership.last_index()
    msg_local_context (
	idx,
    	idx+nidx,
    	idy,
    	idy_maxval,
        istart,
    	ilast,
        to.local_slots.begin(),
        to.local_slots.end(),
        from.local_slots.begin());
    // ---------------------------------------------------------------------------
    // 17) Optimize local exchanges during gatter/scatter
    // ---------------------------------------------------------------------------
    bool has_opt = msg_local_optimize (
        to.local_slots.begin(),
        to.local_slots.end(),
        from.local_slots.begin());

    if (has_opt && n_local != 0) {
        to.local_is_copy       = true; 
        to.local_copy_start    = to.local_slots[0]; 
        to.local_copy_length   = n_local;
        from.local_is_copy     = true;
        from.local_copy_start  = from.local_slots[0];
        from.local_copy_length = n_local;
    }
}
//>mpi_scatter_init:
} // namespace rheolef
#endif // _RHEO_MPI_SCATTER_INIT_H