在c++和MPI中独立并行写入文件

我已经在c++和MPI中实现了一个代码，该代码应该在大约7个文件中为每个CPU处理其数据进行数百万次计算并保存数百万个数字。我使用了大约1万个核心，总共有7万个文件，其中有数百万行代码需要并行编写。

我使用ofstream进行写入，但由于某种原因，MPI代码在中间中断，文件似乎是空的。我希望每个处理器独立地编写其7个文件，而不是所有其他处理器，根据我的搜索，这可以使用MPI完成，但我在许多资源中读到它，我无法理解它如何用于独立编写，并在执行期间动态指定文件名。如果是正确的，谁能尽可能详细地解释一下吗?如果没有，请尽可能详细地解释你的其他建议。

我现在写的东西是这样的:

if (rank == 0)
    {
    if(mkdir("Database",0777)==-1)//creating a directory
    {
    }
    rowsCount = fillCombinations(BCombinations,  RCombinations,
                                 BList,               RList,
                                 maxCombinations,        BIndexBegin, 
                                 BIndexEnd,           RIndexBegin, 
                                 RIndexEnd,    
                                 BCombinationsIndex,  RCombinationsIndex
                          );
}
//then broad cast all the arrays that will be used in all of the computations and at the root 
//send all the indexes to work on on the slaves then at the slave 
or (int cc = BeginIndex ; cc <= EndIndex; cc++)
        {

           // begin by specifying the values that will be used 
           // and making files for each B and R in the list

            BIndex      = betaCombinationsIndex   [cc];
            RIndex     = roughCombinationsIndex  [cc];

            //creating files to save data in and indicating the R and B by their index 
            //specifying files names
           std::string str1;
           std::ostringstream buffer1;
           buffer1 << "Database/";
           str1 = buffer1.str();
           //specifying file names
            std::ostringstream pFileName;
            std::string ppstr2;
            std::ostringstream ppbuffer2;
            ppbuffer2 <<"P_"<<"Beta_"<<(BIndex+1)<<"_Rho_"<<(RIndex+1)<<"_sampledP"<< ".txt";
            ppstr2 = ppbuffer2.str();
            pFileName <<str1.c_str()<<ppstr2.c_str();
            std::string p_file_name = pFileName.str();
            std::ostringstream eFileName;
            std::string eestr2;
            std::ostringstream eebuffer2;
            eebuffer2 <<"E_"<<"Beta_"<<(BIndex+1)<<"_Rho_"<<(RIndex+1)<<"_sampledE"<< ".txt";
            eestr2 = eebuffer2.str();
            eFileName <<str1.c_str()<< eestr2.c_str();
            std::string e_file_name = eFileName.str();
            // and so on for the 7 files .... 

            //creating the files
            ofstream pFile;
            ofstream eFile;
            // and so on for the 7 files .... 
            //opening the files
            pFile      .open (p_file_name.c_str());
            eFile        .open (e_file_name.c_str());
            // and so on for the 7 files .... 
            // then I start the writing in the files and at the end ...

            pFile.close();
            eFile.close();
}
// end of the segment loop