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//
//
// $Id$
//
// 
// -------------------------------------------------------------------
//      GEANT 4 class header file 
//
// Class description:
//
// Class implementing a memory pool for fast allocation and deallocation
// of memory chunks.  The size of the chunks for small allocated objects
// is fixed to 1Kb and takes into account of memory alignment; for large
// objects it is set to 10 times the object's size.
// The implementation is derived from: B.Stroustrup, The C++ Programming
// Language, Third Edition.

//           -------------- G4AllocatorPool ----------------
//
// Author: G.Cosmo (CERN), November 2000
// -------------------------------------------------------------------

#ifndef G4AllocatorPool_h
#define G4AllocatorPool_h 1

class G4AllocatorPool
{
  public:

    explicit G4AllocatorPool( unsigned int n=0 );
      // Create a pool of elements of size n
    ~G4AllocatorPool();
      // Destructor. Return storage to the free store

    inline void* Alloc();
      // Allocate one element
    inline void  Free( void* b );
      // Return an element back to the pool

    inline unsigned int  Size() const;
      // Return storage size
    void  Reset();
      // Return storage to the free store

    inline int  GetNoPages() const;
      // Return the total number of allocated pages
    inline unsigned int  GetPageSize() const;
      // Accessor for default page size
    inline void GrowPageSize( unsigned int factor );
      // Increase default page size by a given factor

  private:

    G4AllocatorPool(const G4AllocatorPool& right);
      // Provate copy constructor
    G4AllocatorPool& operator= (const G4AllocatorPool& right);
      // Private equality operator

    struct G4PoolLink
    {
      G4PoolLink* next;
    };
    class G4PoolChunk
    {
      public:
        explicit G4PoolChunk(unsigned int sz)
          : size(sz), mem(new char[size]), next(0) {;}
        ~G4PoolChunk() { delete [] mem; }
        const unsigned int size;
        char* mem;
        G4PoolChunk* next;
    };

    void Grow();
      // Make pool larger

  private:

    const unsigned int esize;
    unsigned int csize;
    G4PoolChunk* chunks;
    G4PoolLink* head;
    int nchunks;
};

// ------------------------------------------------------------
// Inline implementation
// ------------------------------------------------------------

// ************************************************************
// Alloc
// ************************************************************
//
inline void*
G4AllocatorPool::Alloc()
{
  if (head==0) { Grow(); }
  G4PoolLink* p = head;  // return first element
  head = p->next;
  return p;
}

// ************************************************************
// Free
// ************************************************************
//
inline void
G4AllocatorPool::Free( void* b )
{
  G4PoolLink* p = static_cast<G4PoolLink*>(b);
  p->next = head;        // put b back as first element
  head = p;
}

// ************************************************************
// Size
// ************************************************************
//
inline unsigned int
G4AllocatorPool::Size() const
{
  return nchunks*csize;
}

// ************************************************************
// GetNoPages
// ************************************************************
//
inline int
G4AllocatorPool::GetNoPages() const
{
  return nchunks;
}

// ************************************************************
// GetPageSize
// ************************************************************
//
inline unsigned int
G4AllocatorPool::GetPageSize() const
{
  return csize;
}

// ************************************************************
// GrowPageSize
// ************************************************************
//
inline void
G4AllocatorPool::GrowPageSize( unsigned int sz )
{
  csize = (sz) ? sz*csize : csize; 
}

#endif