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Reference Guide
mp001_fillHistos.C
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1/// \file
2/// \ingroup tutorial_multicore
3/// \notebook -nodraw
4/// Fill histograms in parallel and write them on file.
5/// This example expresses the parallelism of the mt001_fillHistos.C tutorial
6/// with multiprocessing techniques.
7///
8/// \macro_code
9///
10/// \date January 2016
11/// \author Danilo Piparo
12
13// Total amount of numbers
14const UInt_t nNumbers = 20000000U;
15
16// The number of workers
17const UInt_t nWorkers = 4U;
18
19Int_t mp001_fillHistos()
20{
21
22 // We define our work item
23 auto workItem = [](UInt_t workerID) {
24 // One generator, file and ntuple per worker
25 TRandom3 workerRndm(workerID); // Change the seed
26 TFile f(Form("myFile_mp001_%u.root", workerID), "RECREATE");
27 TH1F h(Form("myHisto_%u", workerID), "The Histogram", 64, -4, 4);
28 for (UInt_t i = 0; i < nNumbers; ++i) {
29 h.Fill(workerRndm.Gaus());
30 }
31 h.Write();
32 return 0;
33 };
34
35 // Create the pool of workers
36 ROOT::TProcessExecutor workers(nWorkers);
37
38 // Fill the pool with work
39 workers.Map(workItem, ROOT::TSeqI(nWorkers));
40
41 return 0;
42}
#define f(i)
Definition: RSha256.hxx:104
#define h(i)
Definition: RSha256.hxx:106
int Int_t
Definition: RtypesCore.h:45
unsigned int UInt_t
Definition: RtypesCore.h:46
char * Form(const char *fmt,...)
Formats a string in a circular formatting buffer.
Definition: TString.cxx:2456
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
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition: TFile.h:54
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:577
Random number generator class based on M.
Definition: TRandom3.h:27