StackAllocator.h

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// @(#)root/minuit2:$Id$
// Authors: M. Winkler, F. James, L. Moneta, A. Zsenei   2003-2005

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2005 LCG ROOT Math team,  CERN/PH-SFT                *
 *                                                                    *
 **********************************************************************/

#ifndef ROOT_Minuit2_StackAllocator
#define ROOT_Minuit2_StackAllocator

#include "Minuit2/MnConfig.h"

// comment out this line and recompile if you want to gain additional
// performance (the gain is mainly for "simple" functions which are easy
// to calculate and vanishes quickly if going to cost-intensive functions)
// the library is no longer thread save however

#ifdef MN_USE_STACK_ALLOC
#define _MN_NO_THREAD_SAVE_
#endif

//#include <iostream>



#include <cstdlib>
#include <new>

namespace ROOT {

   namespace Minuit2 {



/// define stack allocator symbol



class StackOverflow {};
class StackError {};
//  using namespace std;

/** StackAllocator controls the memory allocation/deallocation of Minuit. If
    _MN_NO_THREAD_SAVE_ is defined, memory is taken from a pre-allocated piece
    of heap memory which is then used like a stack, otherwise via standard
    malloc/free. Note that defining _MN_NO_THREAD_SAVE_ makes the code thread-
    unsave. The gain in performance is mainly for cost-cheap FCN functions.
 */

class StackAllocator {

public:

//   enum {default_size = 1048576};
  enum {default_size = 524288};

   StackAllocator() :   fStack(0)  {
#ifdef _MN_NO_THREAD_SAVE_
    //std::cout<<"StackAllocator Allocate "<<default_size<<std::endl;
    fStack = new unsigned char[default_size];
#endif
    fStackOffset = 0;
    fBlockCount = 0;
  }

  ~StackAllocator() {
#ifdef _MN_NO_THREAD_SAVE_
    //std::cout<<"StackAllocator destruct "<<fStackOffset<<std::endl;
    if(fStack) delete [] fStack;
#endif
  }

  void* Allocate( size_t nBytes) {
#ifdef _MN_NO_THREAD_SAVE_
    if(fStack == 0) fStack = new unsigned char[default_size];
      int nAlloc = AlignedSize(nBytes);
      CheckOverflow(nAlloc);

//       std::cout << "Allocating " << nAlloc << " bytes, requested = " << nBytes << std::endl;

      // write the start position of the next block at the start of the block
      WriteInt( fStackOffset, fStackOffset+nAlloc);
      // write the start position of the new block at the end of the block
      WriteInt( fStackOffset + nAlloc - sizeof(int), fStackOffset);

      void* result = fStack + fStackOffset + sizeof(int);
      fStackOffset += nAlloc;
      fBlockCount++;

#ifdef DEBUG_ALLOCATOR
      CheckConsistency();
#endif

#else
      void* result = malloc(nBytes);
      if (!result) throw std::bad_alloc();
#endif

      return result;
  }

  void Deallocate( void* p) {
#ifdef _MN_NO_THREAD_SAVE_
      // int previousOffset = ReadInt( fStackOffset - sizeof(int));
      int delBlock = ToInt(p);
      int nextBlock = ReadInt( delBlock);
      int previousBlock = ReadInt( nextBlock - sizeof(int));
      if ( nextBlock == fStackOffset) {
          // deallocating last allocated
         fStackOffset = previousBlock;
      }
      else {
          // overwrite previous adr of next block
         int nextNextBlock = ReadInt(nextBlock);
         WriteInt( nextNextBlock - sizeof(int), previousBlock);
         // overwrite head of deleted block
         WriteInt( previousBlock, nextNextBlock);
      }
      fBlockCount--;

#ifdef DEBUG_ALLOCATOR
      CheckConsistency();
#endif
#else
      free(p);
#endif
      // std::cout << "Block at " << delBlock
      //   << " deallocated, fStackOffset = " << fStackOffset << std::endl;
  }

  int ReadInt( int offset) {
      int* ip = (int*)(fStack+offset);

      // std::cout << "read " << *ip << " from offset " << offset << std::endl;

      return *ip;
  }

  void WriteInt( int offset, int Value) {

      // std::cout << "writing " << Value << " to offset " << offset << std::endl;

      int* ip = reinterpret_cast<int*>(fStack+offset);
      *ip = Value;
  }

  int ToInt( void* p) {
      unsigned char* pc = static_cast<unsigned char*>(p);

     // std::cout << "toInt: p = " << p << " fStack = " << (void*) fStack << std::endl;
     // VC 7.1 warning:conversin from __w64 int to int
      int userBlock = pc - fStack;
      return userBlock - sizeof(int); // correct for starting int
  }

  int AlignedSize( int nBytes) {
      const int fAlignment = 4;
      int needed = nBytes % fAlignment == 0 ? nBytes : (nBytes/fAlignment+1)*fAlignment;
      return needed + 2*sizeof(int);
  }

  void CheckOverflow( int n) {
      if (fStackOffset + n >= default_size) {
         //std::cout << " no more space on stack allocator" << std::endl;
         throw StackOverflow();
      }
  }

  bool CheckConsistency() {

    //std::cout << "checking consistency for " << fBlockCount << " blocks"<< std::endl;

      // loop over all blocks
      int beg = 0;
      int end = fStackOffset;
      int nblocks = 0;
      while (beg < fStackOffset) {
         end = ReadInt( beg);

         // std::cout << "beg = " << beg << " end = " << end
         //     << " fStackOffset = " << fStackOffset << std::endl;

         int beg2 = ReadInt( end - sizeof(int));
         if ( beg != beg2) {
            //std::cout << "  beg != beg2 " << std::endl;
            return false;
         }
         nblocks++;
         beg = end;
      }
     if (end != fStackOffset) {
        //std::cout << " end != fStackOffset" << std::endl;
        return false;
     }
     if (nblocks != fBlockCount) {
        //std::cout << "nblocks != fBlockCount" << std::endl;
        return false;
     }
     //std::cout << "Allocator is in consistent state, nblocks = " << nblocks << std::endl;
     return true;
  }

private:

  unsigned char* fStack;
//   unsigned char fStack[default_size];
  int            fStackOffset;
  int            fBlockCount;

};



class StackAllocatorHolder {

  // t.b.d need to use same trick as  Boost singleton.hpp to be sure that
  // StackAllocator is created before main()

 public:


  static StackAllocator & Get() {
    static StackAllocator gStackAllocator;
    return gStackAllocator;
  }
};



  }  // namespace Minuit2

}  // namespace ROOT

#endif