C++ TFile::GetCacheRead方法代码示例

void h2fast(const char *url , Bool_t draw=kFALSE, Long64_t cachesize=10000000, Int_t learn=1) {
// gEnv->SetValue("TFile.DavixLog", 10);
//  gDebug= 0x02;
   TStopwatch sw;
   TTree* T = NULL;
   sw.Start();
   Long64_t oldb = TFile::GetFileBytesRead();
   TFile *f = TFile::Open(url);
  
   if (!f || f->IsZombie()) {
      printf("File h1big.root does not exist\n");
      exit (-1);
   }
   

//   TTreeCacheUnzip::SetParallelUnzip(TTreeCacheUnzip::kEnable);

   T= (TTree*)f->Get("h42");
   Long64_t nentries = T->GetEntries();
   T->SetCacheSize(cachesize);
   TTreeCache::SetLearnEntries(learn);
   TFileCacheRead *tpf = f->GetCacheRead();
   //tpf->SetEntryRange(0,nentries);
   
   if (draw) T->Draw("rawtr","E33>20");
   else {
      TBranch *brawtr = T->GetBranch("rawtr");
      TBranch *bE33   = T->GetBranch("E33");
      Float_t E33; 
      bE33->SetAddress(&E33);
      for (Long64_t i=0;i<nentries;i++) {
         T->LoadTree(i);
         bE33->GetEntry(i);
         if (E33 > 0) brawtr->GetEntry(i);
      } 
   } 
   if (tpf) tpf->Print();
   printf("Bytes read = %lld\n",TFile::GetFileBytesRead()-oldb);
   printf("Real Time = %7.3f s, CPUtime = %7.3f s\n",sw.RealTime(),sw.CpuTime());
   delete T;
   delete f;
}

//.........这里部分代码省略.........
       // for (Long64_t i=elast-1;i>=efirst;i--) {
       if (i%freq == 0 || i==(elast-1)) fprintf(stderr,"i = %lld\n",i);
       if (r.Rndm() > percententries) continue; 
       T->LoadTree(i);
       if (percentbranches < 1.00) {
         int nb = T->GetListOfBranches()->GetEntries();
         int incr = nb * percentbranches;
         for(int b=0;b<nb; b += incr) ((TBranch*)T->GetListOfBranches()->At(b))->GetEntry(i);   
         int count = 0;
         int maxcount = 1000 + 100 ;
         for(int x = 0; x < maxcount; ++x ) { /* waste cpu */ count = sin(cos((double)count)); }
       } else {
         T->GetEntry(i);
       }
     }
   }

   fprintf(stderr,"Done reading for the first pass, now closing the file\n");
   file->Close();
   delete file;

   //...........................................................................
   // Second read, actually reading the data from cache
   //...........................................................................
   fprintf(stderr,"Opening the file for the 2nd pass\n");
   file = TFile::Open( filename, "TIMEOUT=30" );
   if (!file || file->IsZombie()) return 1;
 
   fprintf(stderr,"The file has been opened, setting up the TTree\n");
   // Try the known names :)
   for (unsigned int i = 0; i < sizeof(names)/sizeof(names[0]); ++i) {
      file->GetObject(names[i], T);
      if (T) break;
   }
   if (T==0) {
     Error("runPrefetchReading","Could not find a tree which the conventional names in %s.",filename.Data());
     return 2;
   }

   TFile::SetReadaheadSize(0);  // (256*1024);
   nentries = T->GetEntries();

   efirst = 0;
   elast  = efirst+nentries;

   if (cachesize == -2) {
      gEnv->SetValue("TFile.AsyncReading", 0);
      cachesize = -1;
   }
   T->SetCacheSize(cachesize);

   if (cachesize != 0) {
      T->SetCacheEntryRange(efirst,elast);
      if (percentbranches < 1.00) {
         int nb = T->GetListOfBranches()->GetEntries();
         int incr = nb * percentbranches;
         for(int b=0;b < nb; b += incr) T->AddBranchToCache(((TBranch*)T->GetListOfBranches()->At(b)),kTRUE);
      } else {
         T->AddBranchToCache("*");
      }
      T->StopCacheLearningPhase();
   }
      
   fprintf(stderr,"Setup done, starting the 2nd reading.\n");
   for (Long64_t i = efirst; i < elast; i++) {
     if (i % freq == 0){
       // for (Long64_t i=elast-1;i>=efirst;i--) {
       if (i%freq == 0 || i==(elast-1)) fprintf(stderr,"i = %lld\n",i);
       if (r.Rndm() > percententries) continue;
       T->LoadTree(i);
       if (percentbranches < 1.00) {
         int nb = T->GetListOfBranches()->GetEntries();
         int incr = nb * percentbranches;
         
         for(int b=0;b<nb; b += incr) {
           ((TBranch*)T->GetListOfBranches()->At(b))->GetEntry(i);
         }
         
         int count = 0;
         int maxcount = 1000 + 100 ;
         for(int x = 0; x < maxcount; ++x ) {
           /* waste cpu */
           count = sin(cos((double)count));
         }         
       } else {
         T->GetEntry(i);
       }
     }
   }
   fprintf(stderr, "Done with the 2nd reading\n");

   fprintf(stderr, "fPrefetchedBlocks = %lli\n", file->GetCacheRead()->GetPrefetchedBlocks());

   fprintf(stderr, "Delete tmp directory: /tmp/xcache\n" );
   if (caching) system( "rm -r /tmp/xcache" );
   
   file->Close();
   delete file;
   return 0;
}