TFilePrefetch.cxx

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// @(#)root/io:$Id$
// Author: Elvin Sindrilaru   19/05/2011

/*************************************************************************
 * Copyright (C) 1995-2011, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

#include "TFilePrefetch.h"
#include "TTimeStamp.h"
#include "TVirtualPerfStats.h"
#include "TVirtualMonitoring.h"

#include <iostream>
#include <string>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cassert>

static const int kMAX_READ_SIZE    = 2;   //maximum size of the read list of blocks

inline int xtod(char c) { return (c>='0' && c<='9') ? c-'0' : ((c>='A' && c<='F') ? c-'A'+10 : ((c>='a' && c<='f') ? c-'a'+10 : 0)); }

using namespace std;

ClassImp(TFilePrefetch)

/**
\class TFilePrefetch
\ingroup IO

The prefetching mechanism uses two classes (TFilePrefetch and
TFPBlock) to prefetch in advance a block of tree entries. There is
a thread which takes care of actually transferring the blocks and
making them available to the main requesting thread. Therefore,
the time spent by the main thread waiting for the data before
processing considerably decreases. Besides the prefetching
mechanisms there is also a local caching option which can be
enabled by the user. Both capabilities are disabled by default
and must be explicitly enabled by the user.
*/


////////////////////////////////////////////////////////////////////////////////
/// Constructor.

TFilePrefetch::TFilePrefetch(TFile* file) :
  fFile(file),
  fConsumer(0),
  fThreadJoined(kTRUE),
  fPrefetchFinished(kFALSE)
{
   fPendingBlocks    = new TList();
   fReadBlocks       = new TList();

   fPendingBlocks->SetOwner();
   fReadBlocks->SetOwner();

   fSemChangeFile    = new TSemaphore(0);
}

////////////////////////////////////////////////////////////////////////////////
/// Destructor

TFilePrefetch::~TFilePrefetch()
{
   if (!fThreadJoined) {
     WaitFinishPrefetch();
   }

   SafeDelete(fConsumer);
   SafeDelete(fPendingBlocks);
   SafeDelete(fReadBlocks);
   SafeDelete(fSemChangeFile);
}


////////////////////////////////////////////////////////////////////////////////
/// Killing the async prefetching thread

void TFilePrefetch::WaitFinishPrefetch()
{
   // Inform the consumer thread that prefetching is over
   {
      std::lock_guard<std::mutex> lk(fMutexPendingList);
      fPrefetchFinished = kTRUE;
   }
   fNewBlockAdded.notify_one();

   fConsumer->Join();
   fThreadJoined = kTRUE;
   fPrefetchFinished = kFALSE;
}


////////////////////////////////////////////////////////////////////////////////
/// Read one block and insert it in prefetchBuffers list.

void TFilePrefetch::ReadAsync(TFPBlock* block, Bool_t &inCache)
{
   char* path = 0;

   if (CheckBlockInCache(path, block)){
      block->SetBuffer(GetBlockFromCache(path, block->GetDataSize()));
      inCache = kTRUE;
   }
   else{
      fFile->ReadBuffers(block->GetBuffer(), block->GetPos(), block->GetLen(), block->GetNoElem());
      if (fFile->GetArchive()) {
         for (Int_t i = 0; i < block->GetNoElem(); i++)
            block->SetPos(i, block->GetPos(i) - fFile->GetArchiveOffset());
      }
      inCache =kFALSE;
   }
   delete[] path;
}

////////////////////////////////////////////////////////////////////////////////
/// Get blocks specified in prefetchBlocks.

void TFilePrefetch::ReadListOfBlocks()
{
   Bool_t inCache = kFALSE;
   TFPBlock*  block = 0;

   while((block = GetPendingBlock())){
      ReadAsync(block, inCache);
      AddReadBlock(block);
      if (!inCache)
         SaveBlockInCache(block);
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Search for a requested element in a block and return the index.

Bool_t TFilePrefetch::BinarySearchReadList(TFPBlock* blockObj, Long64_t offset, Int_t len, Int_t* index)
{
   Int_t first = 0, last = -1, mid = -1;
   last = (Int_t) blockObj->GetNoElem()-1;

   while (first <= last){
      mid = first + (last - first) / 2;
      if ((offset >= blockObj->GetPos(mid) && offset <= (blockObj->GetPos(mid) + blockObj->GetLen(mid))
           && ( (offset + len) <= blockObj->GetPos(mid) + blockObj->GetLen(mid)))){

         *index = mid;
         return true;
      }
      else if (blockObj->GetPos(mid) < offset){
         first = mid + 1;
      }
      else{
         last = mid - 1;
      }
   }
   return false;
}

////////////////////////////////////////////////////////////////////////////////
/// Return the time spent wating for buffer to be read in microseconds.

Long64_t TFilePrefetch::GetWaitTime()
{
   return Long64_t(fWaitTime.RealTime()*1.e+6);
}

////////////////////////////////////////////////////////////////////////////////
/// Return a prefetched element.

Bool_t TFilePrefetch::ReadBuffer(char* buf, Long64_t offset, Int_t len)
{
   Bool_t found = false;
   TFPBlock* blockObj = 0;
   Int_t index = -1;

   std::unique_lock<std::mutex> lk(fMutexReadList);
   while (1){
      TIter iter(fReadBlocks);
      while ((blockObj = (TFPBlock*) iter.Next())){
         index = -1;
         if (BinarySearchReadList(blockObj, offset, len, &index)){
            found = true;
            break;
         }
      }
      if (found)
         break;
      else{
         fWaitTime.Start(kFALSE);
         fReadBlockAdded.wait(lk); //wait for a new block to be added
         fWaitTime.Stop();
      }
   }

   if (found){
      char *pBuff = blockObj->GetPtrToPiece(index);
      pBuff += (offset - blockObj->GetPos(index));
      memcpy(buf, pBuff, len);
   }
   return found;
}

////////////////////////////////////////////////////////////////////////////////
/// Create a TFPBlock object or recycle one and add it to the prefetchBlocks list.

void TFilePrefetch::ReadBlock(Long64_t* offset, Int_t* len, Int_t nblock)
{
   TFPBlock* block = CreateBlockObj(offset, len, nblock);
   AddPendingBlock(block);
}

////////////////////////////////////////////////////////////////////////////////
/// Safe method to add a block to the pendingList.

void TFilePrefetch::AddPendingBlock(TFPBlock* block)
{
   fMutexPendingList.lock();
   fPendingBlocks->Add(block);
   fMutexPendingList.unlock();

   fNewBlockAdded.notify_one();
}

////////////////////////////////////////////////////////////////////////////////
/// Safe method to remove a block from the pendingList.

TFPBlock* TFilePrefetch::GetPendingBlock()
{
   TFPBlock* block = 0;

   // Use the semaphore to deal with the case when the file pointer
   // is changed on the fly by TChain
   fSemChangeFile->Post();
   std::unique_lock<std::mutex> lk(fMutexPendingList);
   // Wait unless there is a pending block or prefetching is over
   fNewBlockAdded.wait(lk, [&]{ return fPendingBlocks->GetSize() > 0 || fPrefetchFinished; });
   lk.unlock();
   fSemChangeFile->Wait();

   lk.lock();
   if (fPendingBlocks->GetSize()){
      block = (TFPBlock*)fPendingBlocks->First();
      block = (TFPBlock*)fPendingBlocks->Remove(block);
   }
   return block;
}

////////////////////////////////////////////////////////////////////////////////
/// Safe method to add a block to the readList.

void TFilePrefetch::AddReadBlock(TFPBlock* block)
{
   fMutexReadList.lock();

   if (fReadBlocks->GetSize() >= kMAX_READ_SIZE){
      TFPBlock* movedBlock = (TFPBlock*) fReadBlocks->First();
      movedBlock = (TFPBlock*)fReadBlocks->Remove(movedBlock);
      delete movedBlock;
      movedBlock = 0;
   }

   fReadBlocks->Add(block);
   fMutexReadList.unlock();

   //signal the addition of a new block
   fReadBlockAdded.notify_one();
}


////////////////////////////////////////////////////////////////////////////////
/// Create a new block or recycle an old one.

TFPBlock* TFilePrefetch::CreateBlockObj(Long64_t* offset, Int_t* len, Int_t noblock)
{
   TFPBlock* blockObj = 0;

   fMutexReadList.lock();

   if (fReadBlocks->GetSize() >= kMAX_READ_SIZE){
      blockObj = static_cast<TFPBlock*>(fReadBlocks->First());
      fReadBlocks->Remove(blockObj);
      fMutexReadList.unlock();
      blockObj->ReallocBlock(offset, len, noblock);
   }
   else{
      fMutexReadList.unlock();
      blockObj = new TFPBlock(offset, len, noblock);
   }
   return blockObj;
}

////////////////////////////////////////////////////////////////////////////////
/// Return reference to the consumer thread.

TThread* TFilePrefetch::GetThread() const
{
   return fConsumer;
}


////////////////////////////////////////////////////////////////////////////////
/// Change the file
///
/// When prefetching is enabled we also need to:
///  - make sure the async thread is not doing any work
///  - clear all blocks from prefetching and read list
///  - reset the file pointer

void TFilePrefetch::SetFile(TFile *file, TFile::ECacheAction action)
{
   if (action == TFile::kDisconnect) {
      if (!fThreadJoined) {
        fSemChangeFile->Wait();
      }

      if (fFile) {
        // Remove all pending and read blocks
        fMutexPendingList.lock();
        fPendingBlocks->Clear();
        fMutexPendingList.unlock();

        fMutexReadList.lock();
        fReadBlocks->Clear();
        fMutexReadList.unlock();
      }

      fFile = file;
      if (!fThreadJoined) {
        fSemChangeFile->Post();
      }
   } else {
      // kDoNotDisconnect must reconnect to the same file
      assert((fFile == file) && "kDoNotDisconnect must reattach to the same file");
   }
}


////////////////////////////////////////////////////////////////////////////////
/// Used to start the consumer thread.

Int_t TFilePrefetch::ThreadStart()
{
   int rc;

   fConsumer = new TThread((TThread::VoidRtnFunc_t) ThreadProc, (void*) this);
   rc = fConsumer->Run();
   if ( !rc ) {
      fThreadJoined = kFALSE;
   }
   return rc;
}


////////////////////////////////////////////////////////////////////////////////
/// Execution loop of the consumer thread.

TThread::VoidRtnFunc_t TFilePrefetch::ThreadProc(void* arg)
{
   TFilePrefetch* pClass = (TFilePrefetch*) arg;

   while (!pClass->IsPrefetchFinished()) {
      pClass->ReadListOfBlocks();
   }

   return (TThread::VoidRtnFunc_t) 1;
}

//############################# CACHING PART ###################################

////////////////////////////////////////////////////////////////////////////////
/// Sum up individual hex values to obtain a decimal value.

Int_t TFilePrefetch::SumHex(const char *hex)
{
   Int_t result = 0;
   const char* ptr = hex;

   for(Int_t i=0; i < (Int_t)strlen(hex); i++)
      result += xtod(ptr[i]);

   return result;
}

////////////////////////////////////////////////////////////////////////////////
/// Test if the block is in cache.

Bool_t TFilePrefetch::CheckBlockInCache(char*& path, TFPBlock* block)
{
   if (fPathCache == "")
      return false;

   Bool_t found = false;
   TString fullPath(fPathCache); // path of the cached files.

   Int_t value = 0;

   if (!gSystem->OpenDirectory(fullPath))
      gSystem->mkdir(fullPath);

   //dir is SHA1 value modulo 16; filename is the value of the SHA1(offset+len)
   TMD5* md = new TMD5();

   TString concatStr;
   for (Int_t i=0; i < block->GetNoElem(); i++){
      concatStr.Form("%lld", block->GetPos(i));
      md->Update((UChar_t*)concatStr.Data(), concatStr.Length());
   }

   md->Final();
   TString fileName( md->AsString() );
   value = SumHex(fileName);
   value = value % 16;
   TString dirName;
   dirName.Form("%i", value);

   fullPath += "/" + dirName + "/" + fileName;

   FileStat_t stat;
   if (gSystem->GetPathInfo(fullPath, stat) == 0) {
      path = new char[fullPath.Length() + 1];
      strlcpy(path, fullPath,fullPath.Length() + 1);
      found = true;
   } else
      found = false;

   delete md;
   return found;
}

////////////////////////////////////////////////////////////////////////////////
/// Return a buffer from cache.

char* TFilePrefetch::GetBlockFromCache(const char* path, Int_t length)
{
   char *buffer = 0;
   TString strPath = path;

   strPath += "?filetype=raw";
   TFile* file = new TFile(strPath);

   Double_t start = 0;
   if (gPerfStats != 0) start = TTimeStamp();

   buffer = (char*) calloc(length, sizeof(char));
   file->ReadBuffer(buffer, 0, length);

   fFile->fBytesRead  += length;
   fFile->fgBytesRead += length;
   fFile->SetReadCalls(fFile->GetReadCalls() + 1);
   fFile->fgReadCalls++;

   if (gMonitoringWriter)
      gMonitoringWriter->SendFileReadProgress(fFile);
   if (gPerfStats != 0) {
      gPerfStats->FileReadEvent(fFile, length, start);
   }

   file->Close();
   delete file;
   return buffer;
}

////////////////////////////////////////////////////////////////////////////////
/// Save the block content in cache.

void TFilePrefetch::SaveBlockInCache(TFPBlock* block)
{
   if (fPathCache == "")
      return;

   //dir is SHA1 value modulo 16; filename is the value of the SHA1
   TMD5* md = new TMD5();

   TString concatStr;
   for(Int_t i=0; i< block->GetNoElem(); i++){
      concatStr.Form("%lld", block->GetPos(i));
      md->Update((UChar_t*)concatStr.Data(), concatStr.Length());
   }
   md->Final();

   TString fileName( md->AsString() );
   Int_t value = SumHex(fileName);
   value = value % 16;

   TString fullPath( fPathCache );
   TString dirName;
   dirName.Form("%i", value);
   fullPath += ("/" + dirName);

   if (!gSystem->OpenDirectory(fullPath))
      gSystem->mkdir(fullPath);

   TFile* file = 0;
   fullPath += ("/" + fileName);
   FileStat_t stat;
   if (gSystem->GetPathInfo(fullPath, stat) == 0) {
      fullPath += "?filetype=raw";
      file = TFile::Open(fullPath, "update");
   } else{
      fullPath += "?filetype=raw";
      file = TFile::Open(fullPath, "new");
   }

   if (file) {
      // coverity[unchecked_value] We do not print error message, have not error
      // return code and close the file anyway, not need to check the return value.
      file->WriteBuffer(block->GetBuffer(), block->GetDataSize());
      file->Close();
      delete file;
   }
   delete md;
}


////////////////////////////////////////////////////////////////////////////////
/// Set the path of the cache directory.

Bool_t TFilePrefetch::SetCache(const char* path)
{
  fPathCache = path;

  if (!gSystem->OpenDirectory(path)){
    return (!gSystem->mkdir(path) ? true : false);
  }

  // Directory already exists
  return true;
}