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Reference Guide
mt304_fillHistos.C
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1/// \file
2/// \ingroup tutorial_multicore
3/// \notebook -draw
4/// Fill histograms in parallel with automatic binning.
5/// Illustrates use of power-of-two autobin algorithm
6///
7/// \macro_code
8/// \macro_image
9///
10/// \date November 2017
11/// \author Gerardo Ganis
12
13// The number of workers
14const UInt_t nWorkers = 8U;
15
16// Reference boundaries
17const Double_t xmiref = -1.;
18const Double_t xmaref = 7.;
19
20Int_t mt304_fillHistos(UInt_t nNumbers = 1001)
21{
22
23 // The first, fundamental operation to be performed in order to make ROOT
24 // thread-aware.
26
27 // Histograms to be filled in parallel
28 ROOT::TThreadedObject<TH1D> h1d("h1d", "1D test histogram", 64, 0., -1.);
29 ROOT::TThreadedObject<TH1D> h1dr("h1dr", "1D test histogram w/ ref boundaries", 64, xmiref, xmaref);
30
31 // We define our work item
32 auto workItem = [&](UInt_t workerID) {
33 // One generator, file and ntuple per worker
34 TRandom3 workerRndm(workerID); // Change the seed
35
36 auto wh1d = h1d.Get();
37 wh1d->SetBit(TH1::kAutoBinPTwo);
38 auto wh1dr = h1dr.Get();
39
40 Double_t x;
41 for (UInt_t i = 0; i < nNumbers; ++i) {
42 x = workerRndm.Gaus(3.);
43 wh1d->Fill(x);
44 wh1dr->Fill(x);
45 }
46 };
47
48 // Create the collection which will hold the threads, our "pool"
49 std::vector<std::thread> workers;
50
51 // Fill the "pool" with workers
52 for (auto workerID : ROOT::TSeqI(nWorkers)) {
53 workers.emplace_back(workItem, workerID);
54 }
55
56 // Now join them
57 for (auto &&worker : workers)
58 worker.join();
59
60 // Merge
61 auto fh1d = h1d.Merge();
62 auto fh1dr = h1dr.Merge();
63
64 // Make the canvas
65 auto c = new TCanvas("c", "c", 800, 800);
66 c->Divide(1, 2);
67
68 gStyle->SetOptStat(111110);
69 c->cd(1);
70 fh1d->DrawCopy();
71 c->cd(2);
72 fh1dr->DrawCopy();
73
74 c->Update();
75
76 return 0;
77}
#define c(i)
Definition: RSha256.hxx:101
int Int_t
Definition: RtypesCore.h:45
unsigned int UInt_t
Definition: RtypesCore.h:46
double Double_t
Definition: RtypesCore.h:59
R__EXTERN TStyle * gStyle
Definition: TStyle.h:414
A pseudo container class which is a generator of indices.
Definition: TSeq.hxx:67
A wrapper to make object instances thread private, lazily.
The Canvas class.
Definition: TCanvas.h:23
@ kAutoBinPTwo
different than 1.
Definition: TH1.h:172
Random number generator class based on M.
Definition: TRandom3.h:27
void SetOptStat(Int_t stat=1)
The type of information printed in the histogram statistics box can be selected via the parameter mod...
Definition: TStyle.cxx:1589
Double_t x[n]
Definition: legend1.C:17
void EnableThreadSafety()
Enables the global mutex to make ROOT thread safe/aware.
Definition: TROOT.cxx:493