Knowing that other facilities like TProcessExecutor might be more adequate for this operation, this tutorial complements mc101, reading and merging. We convey another message with this tutorial: the synergy of ROOT and STL algorithms is possible.
Int_t mt102_readNtuplesFillHistosAndFit()
{
TChain inputChain(
"multiCore");
inputChain.Add("mt101_multiCore_*.root");
TH1F outHisto(
"outHisto",
"Random Numbers", 128, -4, 4);
inputChain.Draw("r >> outHisto");
outHisto.Fit("gaus");
const auto nFiles = inputChain.GetListOfFiles()->GetEntries();
std::vector<TH1F> histograms;
histograms.reserve(nFiles);
for (auto workerID : workerIDs) {
histograms.emplace_back(
TH1F(
Form(
"outHisto_%u", workerID),
"Random Numbers", 128, -4, 4));
}
auto workItem = [&histograms](
UInt_t workerID) {
TFile f(
Form(
"mt101_multiCore_%u.root", workerID));
auto ntuple =
f.Get<
TNtuple>(
"multiCore");
auto &histo = histograms.at(workerID);
for (
auto index :
ROOT::TSeqL(ntuple->GetEntriesFast())) {
histo.
Fill(ntuple->GetArgs()[0]);
}
};
TH1F sumHistogram(
"SumHisto",
"Random Numbers", 128, -4, 4);
std::vector<std::thread> workers;
for (auto workerID : workerIDs) {
workers.emplace_back(workItem, workerID);
}
for (auto &&worker : workers)
worker.join();
std::for_each(std::begin(histograms), std::end(histograms),
[&sumHistogram](
const TH1F &
h) { sumHistogram.Add(&
h); });
sumHistogram.Fit("gaus", 0);
return 0;
}
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void char Point_t Rectangle_t WindowAttributes_t index
char * Form(const char *fmt,...)
Formats a string in a circular formatting buffer.
A chain is a collection of files containing TTree objects.
A ROOT file is composed of a header, followed by consecutive data records (TKey instances) with a wel...
1-D histogram with a float per channel (see TH1 documentation)}
A simple TTree restricted to a list of float variables only.
Int_t Fill() override
Fill a Ntuple with current values in fArgs.
virtual Int_t GetEntry(Long64_t entry, Int_t getall=0)
Read all branches of entry and return total number of bytes read.
This file contains a specialised ROOT message handler to test for diagnostic in unit tests.
void EnableThreadSafety()
Enable support for multi-threading within the ROOT code in particular, enables the global mutex to ma...