Communicator.cpp

#include <algorithm>
#include <array>
#include <iostream>

#include "Communicator.hpp"

// defines types and graph topology
Communicator::Communicator(const MpiEnvironment& env, const Size& gridSize, const Size& tileSize) {
	// Begin definition of basic types
	MPI_Type_contiguous(static_cast<int>(tileSize.Cols), MPI_CHAR, &haloRowType_);
	MPI_Type_commit(&haloRowType_);

	MPI_Type_vector(static_cast<int>(tileSize.Rows), 1, static_cast<int>(tileSize.Cols + 2), MPI_CHAR,
	                &haloColumnType_);
	MPI_Type_commit(&haloColumnType_);

	// End definition of basic types

	// Begin definition of types/displacements for a general cell somewhere in
	// the middle of the procs grid
	const std::array<MPI_Datatype, NoNeighbors> generalSendTypes{{
	    haloCornerType_, haloRowType_, haloCornerType_, //
	    haloColumnType_, haloColumnType_,               //
	    haloCornerType_, haloRowType_, haloCornerType_  //
	}};
	const auto tCols = tileSize.Cols;
	const auto tRows = tileSize.Rows;

	// character coordinates to displacement
	const auto dp = [&](std::size_t x, std::size_t y) { return static_cast<MPI_Aint>(y * (tCols + 2) + x); };

	const std::array<MPI_Aint, NoNeighbors> generalSendDisplacements{{
	    dp(1, 1), dp(1, 1), dp(tCols, 1),            //
	    dp(1, 1), dp(tCols, 1),                      //
	    dp(1, tRows), dp(1, tRows), dp(tCols, tRows) //
	}};

	const std::array<MPI_Aint, NoNeighbors> generalRecvDisplacements{{
	    dp(0, 0), dp(1, 0), dp(tCols + 1, 0),                        //
	    dp(0, 1), dp(tCols + 1, 1),                                  //
	    dp(0, tRows + 1), dp(1, tRows + 1), dp(tCols + 1, tRows + 1) //
	}};

	const std::array<int, NoNeighbors> generalSizes{{
	    1, 1, 1, //
	    1, 1,    //
	    1, 1, 1  //
	}};
	// End definition of datastructures for a general cell

	// Begin definition of datastructures for this particular cell (handle the
	// border cases)
	const auto rank2coord = [&](std::size_t rank) {
		return Coord{
		    rank % gridSize.Cols, //
		    rank / gridSize.Cols  //
		};
	};

	const auto coord2rank = [&](Coord c) { return static_cast<int>(gridSize.Cols * c.Y + c.X); };

	const auto isInsideProcsGrid = [&](Coord c) { return c.X < gridSize.Cols && c.Y < gridSize.Rows; };

	const auto myCoord = rank2coord(env.worldRank());
	const std::array<Coord, NoNeighbors> generalNeighborCoords{{
	    {myCoord.X - 1, myCoord.Y - 1}, // intentional signed underflow
	    {myCoord.X + 0, myCoord.Y - 1}, //
	    {myCoord.X + 1, myCoord.Y - 1}, //
	    {myCoord.X - 1, myCoord.Y + 0}, //
	    {myCoord.X + 1, myCoord.Y + 0}, //
	    {myCoord.X - 1, myCoord.Y + 1}, //
	    {myCoord.X + 0, myCoord.Y + 1}, //
	    {myCoord.X + 1, myCoord.Y + 1}  //
	}};

	for (std::size_t i{0}; i < NoNeighbors; ++i) {
		const auto nbrCoord = generalNeighborCoords[i];
		if (isInsideProcsGrid(nbrCoord)) {
			neighbors_.push_back(coord2rank(nbrCoord));
			sendTypes_.push_back(generalSendTypes[i]);
			sendDisplacements_.push_back(generalSendDisplacements[i]);
			recvDisplacements_.push_back(generalRecvDisplacements[i]);
			sizes_.push_back(generalSizes[i]);
		}
	}

	MPI_Dist_graph_create_adjacent(MPI_COMM_WORLD,                      // comm_old
	                               static_cast<int>(neighbors_.size()), // indegree
	                               neighbors_.data(),                   // sources
	                               static_cast<int*>(MPI_UNWEIGHTED),   // sourceweights
	                               static_cast<int>(neighbors_.size()), // outdegree
	                               neighbors_.data(),                   // destinations
	                               static_cast<int*>(MPI_UNWEIGHTED),   // destweights
	                               MPI_INFO_NULL,                       // info
	                               0,                                   // reorder
	                               &commDistGraph_                      // comm_dist_graph
	                               );
	// End definition of datastructures for this particular cell
}

Communicator::~Communicator() {
	if (commDistGraph_ != MPI_COMM_NULL) {
		MPI_Comm_free(&commDistGraph_);
		MPI_Type_free(&haloColumnType_);
		MPI_Type_free(&haloRowType_);
	}
}

void Communicator::swap(Communicator& first, Communicator& second) {
	using std::swap;
	swap(first.neighbors_, second.neighbors_);
	swap(first.sizes_, second.sizes_);
	swap(first.sendTypes_, second.sendTypes_);
	swap(first.sendDisplacements_, second.sendDisplacements_);
	swap(first.recvDisplacements_, second.recvDisplacements_);
	swap(first.commDistGraph_, second.commDistGraph_);
	swap(first.haloRowType_, second.haloRowType_);
	swap(first.haloColumnType_, second.haloColumnType_);
	swap(first.haloCornerType_, second.haloCornerType_);
}

Communicator::Communicator(Communicator&& other) noexcept { swap(*this, other); }
Communicator& Communicator::operator=(Communicator&& other) noexcept {
	swap(*this, other);
	return *this;
}