TFileCacheWrite.cxx

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// @(#)root/io:$Id$
// Author: Rene Brun   18/05/2006

/*************************************************************************
 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

/**
\class TFileCacheWrite TFileCacheWrite.cxx
\ingroup IO
A cache when writing files over the network

A caching system to speed up network I/O, i.e. when there is
no operating system caching support (like the buffer cache for
local disk I/O). The cache makes sure that every I/O is done with
a (large) fixed length buffer thereby avoiding many small I/O's.
Currently the write cache system is used by the classes TNetFile,
TXNetFile and TWebFile (via TFile::WriteBuffers()).

The write cache is automatically created when writing a remote file
(created in TFile::Open()).
*/


#include "TFile.h"
#include "TFileCacheWrite.h"

ClassImp(TFileCacheWrite);

////////////////////////////////////////////////////////////////////////////////
/// Default Constructor.

TFileCacheWrite::TFileCacheWrite() : TObject()
{
   fBufferSize  = 0;
   fNtot        = 0;
   fSeekStart   = 0;
   fFile        = 0;
   fBuffer      = 0;
   fRecursive   = kFALSE;
}

////////////////////////////////////////////////////////////////////////////////
/// Creates a TFileCacheWrite data structure.
/// The write cache will be connected to file.
/// The size of the cache will be buffersize,
/// if buffersize < 10000 a default size of 512 Kbytes is used

TFileCacheWrite::TFileCacheWrite(TFile *file, Int_t buffersize)
           : TObject()
{
   if (buffersize < 10000) buffersize = 512000;
   fBufferSize  = buffersize;
   fSeekStart   = 0;
   fNtot        = 0;
   fFile        = file;
   fRecursive   = kFALSE;
   fBuffer      = new char[fBufferSize];
   if (file) file->SetCacheWrite(this);
   if (gDebug > 0) Info("TFileCacheWrite","Creating a write cache with buffersize=%d bytes",buffersize);
}

////////////////////////////////////////////////////////////////////////////////
/// Destructor.

TFileCacheWrite::~TFileCacheWrite()
{
   delete [] fBuffer;
}

////////////////////////////////////////////////////////////////////////////////
/// Flush the current write buffer to the file.
/// Returns kTRUE in case of error.

Bool_t TFileCacheWrite::Flush()
{
   if (!fNtot) return kFALSE;
   fFile->Seek(fSeekStart);
   //printf("Flushing buffer at fSeekStart=%lld, fNtot=%d\n",fSeekStart,fNtot);
   fRecursive = kTRUE;
   Bool_t status = fFile->WriteBuffer(fBuffer, fNtot);
   fRecursive = kFALSE;
   fNtot = 0;
   return status;
}

////////////////////////////////////////////////////////////////////////////////
/// Print class internal structure.

void TFileCacheWrite::Print(Option_t *option) const
{
   TString opt = option;
   printf("Write cache for file %s\n",fFile->GetName());
   printf("Size of write cache: %d bytes to be written at %lld\n",fNtot,fSeekStart);
   opt.ToLower();
}

////////////////////////////////////////////////////////////////////////////////
/// Called by the read cache to check if the requested data is not
/// in the write cache buffer.
///        Returns -1 if data not in write cache,
///        0 otherwise.

Int_t TFileCacheWrite::ReadBuffer(char *buf, Long64_t pos, Int_t len)
{
   if (pos < fSeekStart || pos+len > fSeekStart+fNtot) return -1;
   memcpy(buf,fBuffer+pos-fSeekStart,len);
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Write buffer at position pos in the write buffer.
/// The function returns 1 if the buffer has been successfully entered into the write buffer.
/// The function returns 0 in case WriteBuffer() was recusively called via Flush().
/// The function returns -1 in case of error.

Int_t TFileCacheWrite::WriteBuffer(const char *buf, Long64_t pos, Int_t len)
{
   if (fRecursive) return 0;

   //printf("TFileCacheWrite::WriteBuffer, pos=%lld, len=%d, fSeekStart=%lld, fNtot=%d\n",pos,len,fSeekStart,fNtot);

   if (fSeekStart + fNtot != pos) {
      //we must flush the current cache
      if (Flush()) return -1; //failure
   }
   if (fNtot + len >= fBufferSize) {
      if (Flush()) return -1; //failure
      if (len >= fBufferSize) {
         //buffer larger than the cache itself: direct write to file
         fRecursive = kTRUE;
         fFile->Seek(pos); // Flush may have changed this
         if (fFile->WriteBuffer(buf,len)) return -1;  // failure
         fRecursive = kFALSE;
         return 1;
      }
   }
   if (!fNtot) fSeekStart = pos;
   memcpy(fBuffer+fNtot,buf,len);
   fNtot += len;

   return 1;
}

////////////////////////////////////////////////////////////////////////////////
/// Set the file using this cache.
/// Any write not yet flushed will be lost.

void TFileCacheWrite::SetFile(TFile *file)
{
   fFile = file;
}