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mtbb201_parallelHistoFill.C
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1 /// \file
2 /// \ingroup tutorial_multicore
3 /// \notebook
4 /// Parallel fill of a histogram.
5 /// This tutorial shows how a histogram can be filled in parallel
6 /// with a multiprocess approach.
7 ///
8 /// \macro_image
9 /// \macro_code
10 ///
11 /// \date January 2016
12 /// \author Danilo Piparo.
13 
14 const UInt_t poolSize = 4U;
15 
16 Int_t mtbb201_parallelHistoFill()
17 {
18  TH1::AddDirectory(false);
19  ROOT::TThreadExecutor pool(poolSize);
20  auto fillRandomHisto = [](int seed = 0) {
21  TRandom3 rndm(seed);
22  auto h = new TH1F("myHist", "Filled in parallel", 128, -8, 8);
23  for (auto i : ROOT::TSeqI(1000000)) {
24  h->Fill(rndm.Gaus(0, 1));
25  }
26  return h;
27  };
28 
29  auto seeds = ROOT::TSeqI(23);
31  auto sumRandomHisto = pool.MapReduce(fillRandomHisto, seeds, redfunc);
32 
33  auto c = new TCanvas();
34  sumRandomHisto->Draw();
35  return 0;
36 }
c
#define c(i)
Definition: RSha256.hxx:101
ROOT::ExecutorUtils::ReduceObjects
Merge collection of TObjects.
Definition: PoolUtils.h:35
ROOT::TThreadExecutor
This class provides a simple interface to execute the same task multiple times in parallel threads,...
Definition: TThreadExecutor.hxx:40
ROOT::TSeqI
TSeq< int > TSeqI
Definition: TSeq.hxx:194
Int_t
int Int_t
Definition: RtypesCore.h:45
TRandom3
Random number generator class based on M.
Definition: TRandom3.h:27
h
#define h(i)
Definition: RSha256.hxx:106
TH1::AddDirectory
static void AddDirectory(Bool_t add=kTRUE)
Sets the flag controlling the automatic add of histograms in memory.
Definition: TH1.cxx:1282
UInt_t
unsigned int UInt_t
Definition: RtypesCore.h:46
TCanvas
The Canvas class.
Definition: TCanvas.h:23
TH1F
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:575
ROOT::TSeq
A pseudo container class which is a generator of indices.
Definition: TSeq.hxx:66