Maintain MPI version and non-MPI version in a convenient way

I recently used MPI to parallelize my simulation program for acceleration. The way I was adopted was to rewrite one function, which is very time consuming but easy to parallelize.

A simplified model of the program without MPI is as follows:

int main( int argc, char* argv[] ){
    // some declaration here
    Some_OBJ.Serial_Function_1();
    Some_OBJ.Serial_Function_2();
    Some_OBJ.Serial_Function_3(); 
    return 0;
}

While my version is MPI,

#include "mpi.h"
int main( int argc, char* argv[] ){
    // some declaration here
    MPI_Init( NULL, NULL );
    Some_OBJ.Serial_Function_1();
    Some_OBJ.Parallel_Function_2(); // I rewrite this function to replace Some_OBJ.Serial_Function_2();
    Some_OBJ.Serial_Function_3(); 
    MPI_Finalize();
    return 0;
}

I copied my non-MPI code to a new folder, something like mpi_simulation, and add the mpi function by processing the main file. It works, but very inconvenient. If I update some functions, say, OBJ.Serial_Function_1 (), I need to copy the code with care, even if I just changed the constant. There are still slight differences between these software versions. I felt exhausted to keep them in line.

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Update , , . , , , MPI, :

#ifdef USE_MPI
void Some_OBJ::Parallel_Function_2(){
  // ...
}
#endif

MPI , singleton MPI_plugin:

#ifdef USE_MPI
class MPI_plugin{
private:
    static MPI_plugin auto_MPI;
    MPI_plugin(){
      MPI_Init( NULL, NULL );
    }
public:
    ~MPI_plugin(){
      MPI_Finalize();
    }
};
MPI_plugin::MPI_plugin auto_MPI;
#endif

MPI_plugin.h main.cpp MPI_Init() MPI_Finalize() main.cpp MPI. - make "mpi" PHONY:

CPP := mpic++
OTHER_FLAGS := -DUSE_MPI
.PHONY: mpi
mpi: ${MPI_TARGET}
...

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