add minimal example

.gitlab-ci.yml

+test
+  image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc-12
+  script:
+    - spack env activate /opt/spack-environment/
+    - spack load adios2
+    - mkdir build
+    - cd build
+    - cmake ..
+    - make
+    - mpirun --oversubscribe -n 8 ./adios2mini 20000
+    - bpls checkpoint.bp | wc -l

CMakeLists.txt

+cmake_minimum_required(VERSION 3.12)
+project(Adios2Minimal CXX C)
+
+find_package(MPI REQUIRED)
+find_package(ADIOS2 REQUIRED)
+
+add_executable(adios2mini adios2-variable-problem.cpp)
+target_link_libraries(adios2mini PRIVATE adios2::cxx11_mpi)

adios2-variable-problem.cpp

+#include <iostream>
+#include <iomanip>
+#include <mpi.h>
+#include <adios2.h>
+
+std::string createVariable( adios2::IO& io, int counter, int rank, long unsigned int bufferSize ) {
+  std::stringstream sStream;
+  sStream << "Var-" << std::setfill('0') << std::setw(3) << counter << std::setw(3) << "_Rank-" << rank;
+  adios2::Variable< double > var = io.DefineVariable< double >( sStream.str(), {}, {}, {bufferSize} );
+  return sStream.str();
+}
+
+int main( int argc, char ** argv ) {
+
+  std::string outFile = "./checkpoint.bp";
+
+  // -----------
+  //  MPI setup
+  // -----------
+  MPI_Init( &argc, &argv );
+  int commSize;
+  int commRank;
+  MPI_Comm_size( MPI_COMM_WORLD, &commSize );
+  MPI_Comm_rank( MPI_COMM_WORLD, &commRank );
+
+  if( commRank == 0 ) {
+    std::cout << "Executing test with " << commSize << " MPI processes" << std::endl;
+  }
+
+  // determine number of variables to create
+  if( argc != 2 ) {
+    MPI_Abort( MPI_COMM_WORLD, -1 );
+  }
+
+  int numVarTotal = atoi( argv[1] );
+  int numVarLocal = numVarTotal / commSize;
+
+  if( commRank == 0 ) {
+    std::cout << "Total variables asked for = " << numVarTotal << std::endl;
+    std::cout << "Local variables to create = " << numVarLocal << std::endl;
+    numVarLocal += numVarTotal - numVarLocal * commSize;
+  }
+
+  // -------------
+  //  ADIOS setup
+  // -------------
+  adios2::ADIOS adios( MPI_COMM_WORLD );
+  adios2::IO output = adios.DeclareIO( "Writer" );
+  output.SetEngine( "BP5" );
+  adios2::Engine writer = output.Open( outFile, adios2::Mode::Write );
+
+  int counter = 0;
+
+  unsigned long int bufferSize = 100u;
+  std::vector< double > buffer( bufferSize, 2.0 );
+
+  for( int k = 1; k <= numVarLocal; ++k ) {
+    double* address = buffer.data();
+    std::string var = createVariable( output, counter++, commRank, bufferSize );
+    writer.Put< double >( var, address );
+  }
+
+  int numVariables = counter;
+  MPI_Reduce( &counter, &numVariables, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD );
+  if( commRank == 0 ) {
+    std::cout << "Total variables created = " << numVariables << std::endl;
+  }
+
+  // ----------
+  //  Shutdown
+  // ----------
+  writer.Close();
+  MPI_Finalize();
+
+}