Fill histograms in parallel with automatic binning. Illustrates use of power-of-two autobin algorithm
Author: Gerardo Ganis
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Wednesday, April 17, 2024 at 11:15 AM.
const UInt_t nWorkers = 8U;
const Double_t xmiref = -1.;
const Double_t xmaref = 7.;
Arguments are defined.
UInt_t nNumbers = 1001;
The first, fundamental operation to be performed in order to make ROOT thread-aware.
ROOT::EnableThreadSafety();
Histograms to be filled in parallel
ROOT::TThreadedObject<TH1D> h1d("h1d", "1D test histogram", 64, 0., -1.);
ROOT::TThreadedObject<TH1D> h1dr("h1dr", "1D test histogram w/ ref boundaries", 64, xmiref, xmaref);
We define our work item
auto workItem = [&](UInt_t workerID) {
// One generator, file and ntuple per worker
TRandom3 workerRndm(workerID); // Change the seed
auto wh1d = h1d.Get();
wh1d->SetBit(TH1::kAutoBinPTwo);
auto wh1dr = h1dr.Get();
Double_t x;
for (UInt_t i = 0; i < nNumbers; ++i) {
x = workerRndm.Gaus(3.);
wh1d->Fill(x);
wh1dr->Fill(x);
}
};
Create the collection which will hold the threads, our "pool"
std::vector<std::thread> workers;
Fill the "pool" with workers
for (auto workerID : ROOT::TSeqI(nWorkers)) {
workers.emplace_back(workItem, workerID);
}
Now join them
for (auto &&worker : workers)
worker.join();
Merge
auto fh1d = h1d.Merge();
auto fh1dr = h1dr.Merge();
Make the canvas
auto c = new TCanvas("c", "c", 800, 800);
c->Divide(1, 2);
gStyle->SetOptStat(111110);
c->cd(1);
fh1d->DrawCopy();
c->cd(2);
fh1dr->DrawCopy();
c->Update();
return 0;
Draw all canvases
gROOT->GetListOfCanvases()->Draw()