Invoke interpretation within a sub-process to avoid memory hoarding

pe.C

auto memory()
{
   ProcInfo_t info;
   gSystem->GetProcInfo(&info);
   auto mem = info.fMemResident / 1024.;
   printf("Res  memory = %g Mbytes\n", mem);
   return mem;
}

void SubProcessLine(const char *code)
{
   // Really suboptimal from the runtime point of view, but proves the point.
   // Execution of a callable within a process can be optimised wrt to what follows...
   ROOT::TProcessExecutor pe(1);
   pe.Map([code]() { return gInterpreter->ProcessLine(code); }, 1);
}

void ProcessLine(const char *code)
{
   gInterpreter->ProcessLine(code);
}

void pe()
{
   gInterpreter->ProcessLine("TH1F h;");
   sleep(1);
   const auto initMem = memory();
   auto deltaMemSubpr = 0.;
    auto deltaMem = 0.;
    auto nIters=512;
   for (auto i = 0; i < nIters; ++i) {
      SubProcessLine("h");
      if (0 == (i + 1) % (16)) deltaMemSubpr = memory();
   }
    for (auto i = 0; i < nIters; ++i) {
      ProcessLine("h"); // This hoards memory
      if (0 == (i + 1) % 16) deltaMem = memory();
   }
   deltaMemSubpr -= initMem;
   std::cout << "Delta memory subprocess = " << deltaMemSubpr << std::endl;
   deltaMem -= initMem;
   std::cout << "Delta memory classic = " << deltaMem << std::endl;
}