mpi_scatter_begin.h

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#ifndef _RHEO_MPI_SCATTER_BEGIN_H
#define _RHEO_MPI_SCATTER_BEGIN_H
 
# include "rheolef/msg_right_permutation_apply.h"
# include "rheolef/msg_both_permutation_apply.h"
 
namespace rheolef {
/*F:
NAME: mpi_scatter_begin -- gather/scatter initialize (@PACKAGE@ @VERSION@)
DESCRIPTION:
  Begin communication
  for distributed to sequential scatter context.
COMPLEXITY:
IMPLEMENTATION:
  Even though the next routines are written with distributed 
  vectors, either x or y (but not both) may be sequential
  vectors, one for each processor.
  
     from indices indicate where arriving stuff is stashed
     to   indices indicate where departing stuff came from. 
     the naming can be a little confusing.
 
 Reverse scatter is obtained by swapping (to,from)
 in calls to scatter_begin and scatter_end.
 Reverse scatter is useful for transpose matrix-vector multiply.
 
 Scatter general operation is handled by a template "SetOp" type.
 The special case "SetOp=set_op" of an affectation is treated
 separatly, tacking care of local scatter affectation.
 Thus, the "mpi_scatter_begin" routine is split into
 "msg_scatter_begin_global" and "msg_scatter_begin_local"
 parts.
AUTHORS:
    LMC-IMAG, 38041 Grenoble cedex 9, France
    | Pierre.Saramito@imag.fr
DATE:   23 march 1999
END:
*/
 
//<mpi_scatter_begin:
template <
    class InputIterator, 
    class Message, 
    class Tag,
    class Comm>
void
mpi_scatter_begin_global (
    InputIterator                       x,
    Message&                            from,
    Message&                            to,
    Tag                                 tag,
    Comm                                comm)
{
    typedef typename Message::size_type        size_type;
    // ----------------------------------------------------------
    // 1) post receives
    // ----------------------------------------------------------
    from.requests.clear();
    {
      size_type n_receive = from.starts().size() - 1;
      size_type i_start = 0;
      for (size_type i = 0; i < n_receive; i++) {
        size_type i_size = from.starts() [i+1] - from.starts() [i];
        mpi::request i_req = comm.irecv(
            from.procs() [i],
            tag,
            from.values().begin().operator->() + i_start,
            i_size); 
        i_start += i_size;
        from.requests.push_back (std::make_pair(i, i_req));
      }
    } // end block
    // ----------------------------------------------------------
    // 2) apply right permutation
    // ----------------------------------------------------------
    to.load_values (x);
 
    // ----------------------------------------------------------
    // 3) do sends
    // ----------------------------------------------------------
    to.requests.clear();
    {
      size_type n_send = to.starts().size() - 1;
      size_type i_start = 0;
      for (size_type i = 0; i < n_send; i++) {
        size_type i_size = to.starts() [i+1] - to.starts() [i];
        mpi::request i_req = comm.isend(
            to.procs() [i],
            tag,
            to.values().begin().operator->() + i_start,
            i_size); 
        i_start += i_size;
        to.requests.push_back (std::make_pair(i, i_req));
      }
    } // end block
}
template <
    class InputIterator, 
    class OutputIterator, 
    class SetOp, 
    class Message>
void
mpi_scatter_begin_local (
    InputIterator                       x,
    OutputIterator                      y,
    Message&                            from,
    Message&                            to,
    SetOp                               op)
{
#ifdef TO_CLEAN
    msg_both_permutation_apply (
        to.local_slots.begin(),
        to.local_slots.end(),
        x,
        op,
        from.local_slots.begin(),
        y);
#endif // TO_CLEAN
}
// take care of local insert: template specialisation
template <
    class InputIterator, 
    class OutputIterator, 
    class Message>
void
mpi_scatter_begin_local (
    InputIterator                       x,
    OutputIterator                      y,
    Message&                            from,
    Message&                            to,
    details::generic_set_op             op)
{
#ifdef TO_CLEAN
    // used when x & y have distinct pointer types (multi-valued) 
    if (y == x && ! to.local_nonmatching_computed) {
        // scatter_local_optimize(to,from);
        fatal_macro ("y == x: adress matches in scatter: not yet -- sorry");
    } 
    if (to.local_is_copy) {
 
        std::copy(x + to.local_copy_start,
                  x + to.local_copy_start + to.local_copy_length,
                  y + from.local_copy_start);
 
    } else if (y != x || ! to.local_nonmatching_computed) {
 
        msg_both_permutation_apply (
            to.local_slots.begin(),
            to.local_slots.end(),
            x,
            op,
            from.local_slots.begin(),
            y);
 
    } else { // !to.local_is_copy && y == x && to.local_nonmatching_computed
 
        msg_both_permutation_apply (
            to.local_slots_nonmatching.begin(),
            to.local_slots_nonmatching.end(),
            x,
            op,
            from.local_slots_nonmatching.begin(),
            y);
    }
#endif // TO_CLEAN
}
template <
    class InputIterator, 
    class OutputIterator, 
    class Message,
    class SetOp, 
    class Tag,
    class Comm>
inline
void
mpi_scatter_begin(
    InputIterator                       x,
    OutputIterator                      y,
    Message&                            from,
    Message&                            to,
    SetOp                               op,
    Tag                                 tag,
    Comm                                comm)
{
    mpi_scatter_begin_global (x, from, to, tag, comm);
    if (to.n_local() == 0) {
        return;
    }
    error_macro ("local messages: no more supported");
    mpi_scatter_begin_local  (x, y, from, to, op);
}
//>mpi_scatter_begin:
} // namespace rheolef
#endif // _RHEO_MPI_SCATTER_BEGIN_H