void fw() {
//  example showing how to save objects to a file such that they
// can be read in parallel by another Root session.
// Every kUPDATE entries, the current histograms and ntuple
// are written to the file replacing the previous objects
//
// In a different Root session, one can look at the objects without
// reopening the file. See for example macro fr.C
//
//   void fr() {
//   if (gROOT->GetListOfFiles()->FindObject("hsi.root")) {
//      gDirectory->ReadKeys();
//   } else {
//      TFile *file = new TFile("hsi.root");
//   }
//   TNtuple *ntuple = (TNtuple*)gDirectory->Get("ntuple");
//   printf("ntuple has now %d entries\n",ntuple->GetEntries());
//   delete ntuple;
//}
//
// To test this facility, do:
// process1, run root
//       root > .x fw.C
// process2, run a new version of root
//       root > .x fr.C
//       root > .x fr.C, etc
   
  TFile *hfile = new TFile("hsi.root","RECREATE");

// Create some histograms, a profile histogram and an ntuple
  hpx    = new TH1F("hpx","This is the px distribution",100,-4,4);
  hpxpy  = new TH2F("hpxpy","py vs px",40,-4,4,40,-4,4);
  hprof  = new TProfile("hprof","Profile of pz versus px",100,-4,4,0,20);
  ntuple = new TNtuple("ntuple","Demo ntuple","px:py:pz:random:i");

// Fill histograms randomly
  gRandom->SetSeed();
  Float_t px, py, pz;
  const Int_t kUPDATE = 10000;
  Int_t mode = TObject::kWriteDelete;
  for (Int_t i = 0; i < 25000000; i++) {
     gRandom->Rannor(px,py);
     pz = px*px + py*py;
     Float_t random = gRandom->Rndm(1);
     hpx->Fill(px);
     hpxpy->Fill(px,py);
     hprof->Fill(px,pz);
     ntuple->Fill(px,py,pz,random,i);
     if (i && (i%kUPDATE) == 0) {
        hpx->Write(0,mode);
        hpxpy->Write(0,mode);
        hprof->Write(0,mode);
        ntuple->Write(0,mode);
        hfile->SaveSelf(); //this is the key statement
     }
  }
  hfile->Write();
}