mpi_permutation.h

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#pragma once
#include <map>
#include <thrust/host_vector.h>
#include "index.h"
#include "mpi_datatype.h"
#include "tensor_traits.h"
#include "tensor_traits_scalar.h"
#include "tensor_traits_thrust.h"
#include "tensor_traits_std.h"
 
 
namespace dg{
 
template<class MessageType>
bool is_communicating(
    const std::map<int,MessageType>& messages,
    MPI_Comm comm)
{
    int comm_size;
    MPI_Comm_size( comm, &comm_size);
    thrust::host_vector<int> sendTo( comm_size, 0 );
    thrust::host_vector<int> global( comm_size*comm_size);
    auto flat_vals = detail::flatten_values( messages);
    for( auto& send : flat_vals)
        sendTo[send.first] = send.second.size();
    // everyone knows howmany messages everyone is sending
    MPI_Allgather( sendTo.data(), comm_size, MPI_INT,
                   global.data(), comm_size, MPI_INT,
                   comm);
    bool isCommunicating = false;
    for( int i=0; i<comm_size; i++)
        for( int k=0; k<comm_size; k++)
            if( k != i and global[i*comm_size+k] != 0)
                isCommunicating = true;
    return isCommunicating;
}
 
 
template<class MessageType>
std::map<int,MessageType> mpi_permute(
    const std::map<int,MessageType>& messages,
    MPI_Comm comm)
{
    // I think this function is fairly intuitive to understand which is good
    int rank, comm_size;
    MPI_Comm_rank( comm, &rank);
    MPI_Comm_size( comm, &comm_size);
    thrust::host_vector<int> sendTo( comm_size, 0 ), recvFrom( comm_size, 0);
    thrust::host_vector<int> global( comm_size*comm_size);
    auto flat_vals = detail::flatten_values( messages);
    for( auto& send : flat_vals)
    {
        sendTo[send.first] = send.second.size();
    }
    // everyone knows howmany messages everyone is sending
    MPI_Allgather( sendTo.data(), comm_size, MPI_INT,
                   global.data(), comm_size, MPI_INT,
                   comm);
    for( int i=0; i<comm_size; i++)
        recvFrom[i] = global[i*comm_size+rank];
    // Now we can use Alltoallv to send
    thrust::host_vector<int> accS( comm_size), accR(comm_size);
    thrust::exclusive_scan( sendTo.begin(), sendTo.end(), accS.begin());
    thrust::exclusive_scan( recvFrom.begin(), recvFrom.end(), accR.begin());
 
    auto send = detail::flatten_map( flat_vals);
    using value_type = dg::get_value_type<decltype(send)>;
    thrust::host_vector<value_type> recv(
        thrust::reduce( recvFrom.begin(), recvFrom.end()));
    void * send_ptr          = thrust::raw_pointer_cast( send.data());
    const int * sendTo_ptr   = thrust::raw_pointer_cast( sendTo.data());
    const int * accS_ptr     = thrust::raw_pointer_cast( accS.data());
    void * recv_ptr          = thrust::raw_pointer_cast( recv.data());
    const int * recvFrom_ptr = thrust::raw_pointer_cast( recvFrom.data());
    const int * accR_ptr     = thrust::raw_pointer_cast( accR.data());
    MPI_Datatype type = dg::getMPIDataType<value_type>();
    MPI_Alltoallv( send_ptr, sendTo_ptr,   accS_ptr, type,
                   recv_ptr, recvFrom_ptr, accR_ptr, type,
                   comm);
    return detail::make_map_t<MessageType>( recv, detail::make_size_map( recvFrom) );
}
 
template<class ContainerType>
void mpi_gather( const thrust::host_vector<std::array<int,2>>& gather_map,
    const ContainerType& gatherFrom, ContainerType& result, MPI_Comm comm)
{
    thrust::host_vector<int> bufferIdx;
    auto gather_m = gIdx2unique_idx( gather_map, bufferIdx);
    auto send_map = mpi_permute(gather_m, comm);
    auto gather = detail::flatten_map( send_map);
    auto size_map = detail::get_size_map( send_map);
    ContainerType res( gather.size());
    thrust::gather( gather.begin(), gather.end(), gatherFrom.begin(), res.begin());
    std::map<int,ContainerType> result_map = detail::make_map_t<ContainerType>( res, size_map);
    std::map<int,ContainerType> recv = mpi_permute( result_map, comm);
    ContainerType flat = detail::flatten_map( recv);
    result.resize( bufferIdx.size());
    thrust::gather( bufferIdx.begin(), bufferIdx.end(), flat.begin(), result.begin());
}
template<class ContainerType>
void mpi_scatter( const thrust::host_vector<std::array<int,2>>& scatter_map,
    const ContainerType& toScatter, ContainerType& result,
    MPI_Comm comm,
    bool resize_result = false
    )
{
    thrust::host_vector<int> bufferIdx;
    // must be injective
    auto scatter_m = gIdx2unique_idx( scatter_map, bufferIdx);
    auto recv_map = mpi_permute(scatter_m, comm);
    auto scatter = detail::flatten_map( recv_map);
 
    auto size_map = detail::get_size_map( scatter_m);
 
    ContainerType to_send( toScatter);
    thrust::scatter( toScatter.begin(), toScatter.end(), bufferIdx.begin(), to_send.begin());
 
    auto send = detail::make_map_t<ContainerType>( to_send, size_map);
    auto result_map = mpi_permute( send, comm);
    auto res = detail::flatten_map( result_map);
    if( resize_result)
        result.resize( res.size());
    thrust::scatter( res.begin(), res.end(), scatter.begin(), result.begin());
}
 
template<class Integer>
thrust::host_vector<std::array<Integer,2>>
    mpi_invert_permutation( const thrust::host_vector<std::array<Integer,2>>& p,
            MPI_Comm comm)
{
    thrust::host_vector<Integer> seq( p.size());
    thrust::host_vector<std::array<Integer,2>> seq_arr( p.size());
    thrust::sequence( seq.begin(), seq.end());
    Integer rank;
    MPI_Comm_rank( comm, &rank);
    // package sequence
    for( unsigned u=0; u<seq.size(); u++)
        seq_arr[u] = {rank, seq[u]};
    thrust::host_vector<std::array<Integer,2>> sort_map;
    mpi_scatter( p, seq_arr, sort_map, comm, true);
    return sort_map;
 
}
 
 
} // namespace dg