mp_processSelector.C

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/// \file
/// \ingroup tutorial_analysis_parallel
/// \notebook -nodraw
/// Illustrate the usage of the multiprocessing TTreeProcessorMP
/// and TSelector interfaces with the h1analysis.C example.
///
/// \macro_code
///
/// \authors Anda Chelba, Gerardo Ganis
 
#include "TString.h"
#include "TROOT.h"
#include "TChain.h"
#include "TBranch.h"
#include "TFileCollection.h"
#include "TH1F.h"
#include "TTreeReader.h"
#include "ROOT/TTreeProcessorMP.hxx"
 
#include <memory>
 
const auto file0 = "root://eospublic.cern.ch//eos/root-eos/h1/dstarmb.root";
const std::vector<std::string> files = {file0,
                                        "root://eospublic.cern.ch//eos/root-eos/h1/dstarp1a.root",
                                        "root://eospublic.cern.ch//eos/root-eos/h1/dstarp1b.root",
                                        "root://eospublic.cern.ch//eos/root-eos/h1/dstarp2.root"};
 
int mp_processSelector()
{
 
   // MacOSX may generate connection to WindowServer errors
   gROOT->SetBatch(kTRUE);
 
   TString selectorPath = gROOT->GetTutorialDir();
   selectorPath += "/analysis/tree/h1analysis.C+";
   std::cout << "selector used is: " << selectorPath << "\n";
   auto sel = TSelector::GetSelector(selectorPath);
 
// The following code generates a crash when Davix is used for HTTP
// Davix does not seem fork-safe; the problem has been reported to the
// Davix developers. For the time being we disable this part.
// To repoduce the problem, uncomment the next line.
//
// #define __reproduce_davix
#if defined(__reproduce_davix)
   auto fp = std::make_unique<TTree>(TFile::Open(file0));
   auto tree = fp->Get<TTree>("h42");
#endif
 
   ROOT::TTreeProcessorMP pool(3);
 
   TList *out = nullptr;
#if defined(__reproduce_davix)
   // TTreeProcessorMP::Process with a single tree
   out = pool.Process(*tree, *sel);
   sel->GetOutputList()->Delete();
#endif
 
   // TTreeProcessorMP::Process with single file name and tree name
   // Note: we have less files than workers here
   out = pool.Process(file0, *sel, "h42");
   sel->GetOutputList()->Delete();
 
   // Prepare datasets: vector of files, TFileCollection
   TChain ch;
   TFileCollection fc;
   for (auto &&file : files) {
      fc.Add(new TFileInfo(file.c_str()));
      ch.Add(file.c_str());
   }
 
   // TTreeProcessorMP::Process with vector of files and tree name
   // Note: we have more files than workers here (different behaviour)
   out = pool.Process(files, *sel, "h42");
   sel->GetOutputList()->Delete();
 
   // TTreeProcessorMP::Process with TFileCollection, no tree name
   out = pool.Process(fc, *sel);
   sel->GetOutputList()->Delete();
 
   // TTreeProcessorMP::Process with TChain, no tree name
   out = pool.Process(ch, *sel);
   sel->GetOutputList()->Delete();
 
   return 0;
}