const UInt_t nNumbers = 20000000U;

const UInt_t nWorkers = 4U;

const auto workSize = nNumbers / nWorkers;

%%cpp -d
void fillRandom(TNtuple &ntuple, TRandom3 &rndm, UInt_t n)
{
   for (auto i : ROOT::TSeqI(n))
      ntuple.Fill(rndm.Gaus());
}

gROOT->SetBatch();

TRandom3 rndm(1);
TFile ofile("mt101_singleCore.root", "RECREATE");
TNtuple randomNumbers("singleCore", "Random Numbers", "r");
fillRandom(randomNumbers, rndm, nNumbers);
randomNumbers.Write();
ofile.Close();

ROOT::EnableThreadSafety();

auto workItem = [](UInt_t workerID) {
   // One generator, file and ntuple per worker
   TRandom3 workerRndm(workerID); // Change the seed
   TFile ofile(Form("mt101_multiCore_%u.root", workerID), "RECREATE");
   TNtuple workerRandomNumbers("multiCore", "Random Numbers", "r");
   fillRandom(workerRandomNumbers, workerRndm, workSize);
   workerRandomNumbers.Write();
   return 0;
};

std::vector<std::thread> workers;

for (auto workerID : ROOT::TSeqI(nWorkers)) {
   workers.emplace_back(workItem, workerID);
}

for (auto &&worker : workers)
   worker.join();

return 0;

gROOT->GetListOfCanvases()->Draw()