// Copyright (C) 2005-2006 Douglas Gregor <doug.gregor -at- gmail.com>.



// Use, modification and distribution is subject to the Boost Software

// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)



// Message Passing Interface 1.1 -- Section 4.7. Gather-to-all

#ifndef BOOST_MPI_ALL_GATHER_HPP

#define BOOST_MPI_ALL_GATHER_HPP



#include <boost/mpi/exception.hpp>

#include <boost/mpi/datatype.hpp>

#include <vector>

#include <boost/serialization/vector.hpp>



// all_gather falls back to gather+broadcast in some cases

#include <boost/mpi/collectives/broadcast.hpp>

#include <boost/mpi/collectives/gather.hpp>



namespace boost { namespace mpi {



namespace detail {

  // We're all-gathering for a type that has an associated MPI

  // datatype, so we'll use MPI_Gather to do all of the work.

  template<typename T>

  void

  all_gather_impl(const communicator& comm, const T* in_values, int n, 

                  T* out_values, mpl::true_)

  {

    MPI_Datatype type = boost::mpi::get_mpi_datatype<T>(*in_values);

    BOOST_MPI_CHECK_RESULT(MPI_Allgather,

                           (const_cast<T*>(in_values), n, type,

                            out_values, n, type, comm));

  }



  // We're all-gathering for a type that has no associated MPI

  // type. So, we'll do a manual gather followed by a broadcast.

  template<typename T>

  void

  all_gather_impl(const communicator& comm, const T* in_values, int n, 

                  T* out_values, mpl::false_)

  {

    std::cerr << comm.rank() << ": gathering " << n << " values to root 0..." << std::endl;

    std::cerr << in_values << ", " << out_values << std::endl;

    gather(comm, in_values, n, out_values, 0);

    std::cerr << comm.rank() << ":  broadcasting from root 0..." << std::endl;

    broadcast(comm, out_values, comm.size() * n, 0);

  }

} // end namespace detail



template<typename T>

inline void

all_gather(const communicator& comm, const T& in_value, T* out_values)

{

  detail::all_gather_impl(comm, &in_value, 1, out_values, is_mpi_datatype<T>());

}



template<typename T>

void

all_gather(const communicator& comm, const T& in_value, 

           std::vector<T>& out_values)

{

  out_values.resize(comm.size());

  ::boost::mpi::all_gather(comm, &in_value, 1, &out_values[0]);

}



template<typename T>

inline void

all_gather(const communicator& comm, const T* in_values, int n, T* out_values)

{

  detail::all_gather_impl(comm, in_values, n, out_values, is_mpi_datatype<T>());

}



template<typename T>

void

all_gather(const communicator& comm, const T* in_values, int n,

           std::vector<T>& out_values)

{

  out_values.resize(comm.size() * n);

  ::boost::mpi::all_gather(comm, in_values, n, &out_values[0]);

}



} } // end namespace boost::mpi



#endif // BOOST_MPI_ALL_GATHER_HPP

