ROOT I/O

README.md

Reading ROOT data benchmarks

• write a benchmark for reading ROOT files (with the Scanner types)
• input file generated with the attached C++ program
  • /data/f64s-scalar.root on clrmastergo

ROOT I/O main classes

• TFile:
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/inc/TFile.h
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/src/TFile.cxx
• TDirectoryFile:
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/inc/TDirectoryFile.h
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/src/TDirectoryFile.cxx
• TKey:
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/inc/TKey.h
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/src/TKey.cxx
• TBuffer:
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/inc/TBufferFile.h
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/src/TBufferFile.cxx
• TStreamerInfo:
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/inc/TStreamerInfo.h
  • https://github.com/root-project/root/blob/v6-12-00-patches/io/io/src/TStreamerInfo.cxx

ROOT output implementation

• Creation of a simple ROOT file readable by ROOT C++ and Go-HEP/rootio
  • write a ROOT file that is empty (but contains the needed information(s) to be interpretable and readable by C++ and Go)
  • write a ROOT file that contains a TObjString of name "foo" and title "bar"
  • write a ROOT file that only contains a TH1D (a 1-dimension histogram filled with Doubles)

gen-data.cxx

#include <string>

#include "TTree.h"
#include "TFile.h"
#include "TRandom.h"
#include "TString.h"

int main(int argc, char **argv) {
	auto f = TFile::Open("f64s.root", "recreate");
	f->SetCompressionLevel(0);
	auto t = new TTree("tree","tree");

	const Long_t EVTMAX = 1000000;
	const Long_t BRANCHES = 1;

	const std::string fname = "f64s.root";

	Double_t v[BRANCHES];
	for (int i = 0; i < BRANCHES; i++) {
		auto n = TString::Format("Scalar_%d", i);
		auto b = TString::Format("Scalar_%d/D", i);
		t->Branch(n, &v[i], b);
	}

	for ( Long_t i = 0; i <EVTMAX;i++) {
		for (int j = 0; j < BRANCHES; j++) {
			v[j]=gRandom->Gaus();
		}
		t->Fill();
	}

	f->Write();
	f->Close();
}