Fill histograms in parallel and write them on file. The simplest meaningful possible example which shows ROOT thread awareness.
Author: Danilo Piparo
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 nNumbers = 20000000U;
const UInt_t nWorkers = 4U;
The first, fundamental operation to be performed in order to make ROOT thread-aware.
ROOT::EnableThreadSafety();
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_mt001_%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();
};
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();
return 0;
Draw all canvases
gROOT->GetListOfCanvases()->Draw()