Add new MPI helper: collectStringsTo()

Author: franzpoeschel

CMakeLists.txt

@@ -353,6 +353,7 @@ set(CORE_SOURCE
         src/auxiliary/Date.cpp
         src/auxiliary/Filesystem.cpp
         src/auxiliary/JSON.cpp
+        src/auxiliary/MPI.cpp
         src/backend/Attributable.cpp
         src/backend/BaseRecordComponent.cpp
         src/backend/MeshRecordComponent.cpp

include/openPMD/auxiliary/MPI.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "openPMD/config.hpp"
+
+#if openPMD_HAVE_MPI
+
+#    include <mpi.h>
+#    include <string>
+#    include <vector>
+
+namespace openPMD
+{
+namespace auxiliary
+{
+    std::vector< std::string >
+    collectStringsTo(
+        MPI_Comm communicator,
+        int destRank,
+        std::string const & thisRankString );
+
+    std::vector< std::string >
+    distributeStringsToAllRanks(
+        MPI_Comm communicator,
+        std::string const & thisRankString );
+} // namespace auxiliary
+} // namespace openPMD
+#endif

src/auxiliary/MPI.cpp

@@ -0,0 +1,130 @@
+#include "openPMD/auxiliary/MPI.hpp"
+
+#if openPMD_HAVE_MPI
+
+namespace openPMD
+{
+namespace auxiliary
+{
+    std::vector< std::string >
+    collectStringsTo(
+        MPI_Comm communicator,
+        int destRank,
+        std::string const & thisRankString )
+    {
+        int rank, size;
+        MPI_Comm_rank( communicator, &rank );
+        MPI_Comm_size( communicator, &size );
+        int sendLength = thisRankString.size() + 1;
+
+        int * sizesBuffer = nullptr;
+        int * displs = nullptr;
+        if( rank == destRank )
+        {
+            sizesBuffer = new int[ size ];
+            displs = new int[ size ];
+        }
+
+        MPI_Gather(
+            &sendLength,
+            1,
+            MPI_INT,
+            sizesBuffer,
+            1,
+            MPI_INT,
+            destRank,
+            MPI_COMM_WORLD );
+
+        char * namesBuffer = nullptr;
+        if( rank == destRank )
+        {
+            size_t sum = 0;
+            for( int i = 0; i < size; ++i )
+            {
+                displs[ i ] = sum;
+                sum += sizesBuffer[ i ];
+            }
+            namesBuffer = new char[ sum ];
+        }
+
+        MPI_Gatherv(
+            thisRankString.c_str(),
+            sendLength,
+            MPI_CHAR,
+            namesBuffer,
+            sizesBuffer,
+            displs,
+            MPI_CHAR,
+            destRank,
+            MPI_COMM_WORLD );
+
+        if( rank == destRank )
+        {
+            std::vector< std::string > hostnames( size );
+            for( int i = 0; i < size; ++i )
+            {
+                hostnames[ i ] = std::string( namesBuffer + displs[ i ] );
+            }
+
+            delete[] sizesBuffer;
+            delete[] displs;
+            delete[] namesBuffer;
+            return hostnames;
+        }
+        else
+        {
+            return std::vector< std::string >();
+        }
+    }
+
+    std::vector< std::string >
+    distributeStringsToAllRanks(
+        MPI_Comm communicator,
+        std::string const & thisRankString )
+    {
+        int rank, size;
+        MPI_Comm_rank( communicator, &rank );
+        MPI_Comm_size( communicator, &size );
+        int sendLength = thisRankString.size() + 1;
+
+        int * sizesBuffer = new int[ size ];
+        int * displs = new int[ size ];
+
+        MPI_Allgather(
+            &sendLength, 1, MPI_INT, sizesBuffer, 1, MPI_INT, MPI_COMM_WORLD );
+
+        char * namesBuffer;
+        {
+            size_t sum = 0;
+            for( int i = 0; i < size; ++i )
+            {
+                displs[ i ] = sum;
+                sum += sizesBuffer[ i ];
+            }
+            namesBuffer = new char[ sum ];
+        }
+
+        MPI_Allgatherv(
+            thisRankString.c_str(),
+            sendLength,
+            MPI_CHAR,
+            namesBuffer,
+            sizesBuffer,
+            displs,
+            MPI_CHAR,
+            MPI_COMM_WORLD );
+
+        std::vector< std::string > hostnames( size );
+        for( int i = 0; i < size; ++i )
+        {
+            hostnames[ i ] = std::string( namesBuffer + displs[ i ] );
+        }
+
+        delete[] sizesBuffer;
+        delete[] displs;
+        delete[] namesBuffer;
+        return hostnames;
+    }
+} // namespace auxiliary
+} // namespace openPMD
+#endif