mtbb001_fillHistos.C
/// \file
/// \ingroup tutorial_multicore
/// \notebook
/// Fill histograms in parallel and write them on file.
/// This example expresses the parallelism of the mt001_fillHistos.C tutorial
/// with multiprocessing techniques.
///
/// \macro_code
///
/// \date January 2016
/// \author Danilo Piparo
// Total amount of numbers
const UInt_t nNumbers = 20000000U;
// The number of workers
const UInt_t nThreads = 4U;
Int_t mtbb001_fillHistos()
{
// We define our work item
auto workItem = [](UInt_t workerID) {
// One generator, file and ntuple per worker
TRandom3 workerRndm(workerID); // Change the seed
TFile f(Form("myFile_mtbb001_%u.root", workerID), "RECREATE");
TH1F h(Form("myHisto_%u", workerID), "The Histogram", 64, -4, 4);
for (UInt_t i = 0; i < nNumbers; ++i) {
h.Fill(workerRndm.Gaus());
}
h.Write();
return 0;
};
// Create the pool of threads
ROOT::TThreadExecutor pool(nThreads);
// Fill the pool with work
pool.Map(workItem, ROOT::TSeqI(nThreads));
return 0;
}