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Reference Guide
mp001_fillHistos.C File Reference

Detailed Description

View in nbviewer Open in SWAN 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) {
h.Fill(workerRndm.Gaus());
}
h.Write();
return 0;
};
// Create the pool of workers
ROOT::TProcessExecutor workers(nWorkers);
// Fill the pool with work
workers.Map(workItem, ROOT::TSeqI(nWorkers));
return 0;
}
Date
January 2016
Author
Danilo Piparo

Definition in file mp001_fillHistos.C.

f
#define f(i)
Definition: RSha256.hxx:122
Form
char * Form(const char *fmt,...)
Int_t
int Int_t
Definition: RtypesCore.h:45
TRandom3
Definition: TRandom3.h:27
h
#define h(i)
Definition: RSha256.hxx:124
UInt_t
unsigned int UInt_t
Definition: RtypesCore.h:46
TFile
Definition: TFile.h:54
ROOT::TProcessExecutor
This class provides a simple interface to execute the same task multiple times in parallel,...
Definition: TProcessExecutor.hxx:41
TH1F
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:572
ROOT::TSeq
A pseudo container class which is a generator of indices.
Definition: TSeq.hxx:66