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mp001_fillHistos.C File Reference

Detailed Description

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Fill histograms in parallel and write them on file.

This example expresses the parallelism of the mt001_fillHistos.C tutorial with multiprocessing techniques.

// Total amount of numbers
const UInt_t nNumbers = 20000000U;
// The number of workers
const UInt_t nWorkers = 4U;
Int_t mp001_fillHistos()
// We define our work item
auto workItem = [](UInt_t workerID) {
// One generator, file and ntuple per worker
TRandom3 workerRndm(workerID); // Change the seed
TFile f(Form("myFile_mp001_%u.root", workerID), "RECREATE");
TH1F h(Form("myHisto_%u", workerID), "The Histogram", 64, -4, 4);
for (UInt_t i = 0; i < nNumbers; ++i) {
return 0;
// Create the pool of workers
ROOT::TProcessExecutor workers(nWorkers);
// Fill the pool with work
workers.Map(workItem, ROOT::TSeqI(nWorkers));
return 0;
#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:2467
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 composed of a header, followed by consecutive data records (TKey instances) with a wel...
Definition TFile.h:53
1-D histogram with a float per channel (see TH1 documentation)}
Definition TH1.h:578
Random number generator class based on M.
Definition TRandom3.h:27
January 2016
Danilo Piparo

Definition in file mp001_fillHistos.C.