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Reference Guide
mtbb001_fillHistos.C
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1/// \file
2/// \ingroup tutorial_multicore
3/// \notebook
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 nThreads = 4U;
18
19Int_t mtbb001_fillHistos()
20{
21 // We define our work item
22 auto workItem = [](UInt_t workerID) {
23 // One generator, file and ntuple per worker
24 TRandom3 workerRndm(workerID); // Change the seed
25 TFile f(Form("myFile_mtbb001_%u.root", workerID), "RECREATE");
26 TH1F h(Form("myHisto_%u", workerID), "The Histogram", 64, -4, 4);
27 for (UInt_t i = 0; i < nNumbers; ++i) {
28 h.Fill(workerRndm.Gaus());
29 }
30 h.Write();
31 return 0;
32 };
33
34 // Create the pool of threads
35 ROOT::TThreadExecutor pool(nThreads);
36
37 // Fill the pool with work
38 pool.Map(workItem, ROOT::TSeqI(nThreads));
39 return 0;
40}
#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
A pseudo container class which is a generator of indices.
Definition: TSeq.hxx:67
This class provides a simple interface to execute the same task multiple times in parallel threads,...
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