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mp201_parallelHistoFill.C
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1/// \file
2/// \ingroup tutorial_multicore
3/// \notebook -js
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
14const UInt_t poolSize = 4U;
15
16Int_t mp201_parallelHistoFill()
17{
18 TH1::AddDirectory(false);
19 ROOT::TProcessExecutor 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}
#define c(i)
Definition: RSha256.hxx:101
#define h(i)
Definition: RSha256.hxx:106
int Int_t
Definition: RtypesCore.h:45
unsigned int UInt_t
Definition: RtypesCore.h:46
Merge collection of TObjects.
Definition: PoolUtils.h:35
This class provides a simple interface to execute the same task multiple times in parallel,...
A pseudo container class which is a generator of indices.
Definition: TSeq.hxx:67
The Canvas class.
Definition: TCanvas.h:23
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:577
static void AddDirectory(Bool_t add=kTRUE)
Sets the flag controlling the automatic add of histograms in memory.
Definition: TH1.cxx:1267
Random number generator class based on M.
Definition: TRandom3.h:27
TSeq< int > TSeqI
Definition: TSeq.hxx:203