Pool.hpp

/*
   Copyright (C) 2003-2006 MySQL AB
    All rights reserved. Use is subject to license terms.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
*/

#ifndef FOR_LIB_POOL_H
#define FOR_LIB_POOL_H

 
//===========================================================================
//
// .PUBLIC
//
//===========================================================================
 
//
// enum { defInitSize = 256, defIncSize  = 64 }; 
// Description: type to store initial and incremental size in.
//
//
// Pool(int anInitSize = defInitSize, int anIncSize = defIncSize);
// Description:
//   Constructor. Allocates anInitSize of objects <template argument>.
//   When the pool runs out of elements, anIncSize elements are added to the
//   pool. (When the pool is not optimized to allocate multiple elements
//   more efficient, the anIncSize MUST be set to 1 to get the best
//   performance...
//
// Parameters:
//   defInitSize: Initial size of the pool (# of elements in the pool)
//   defIncSize:  # of elements added to the pool when a request to an empty
//    pool is made.
// Return value:
//      _ 
// Errors:
//      -
// Asserts:
//   _
//
//
// virtual ~Pool();
// Description:
//   Elements in the pool are all deallocated.
// Parameters:
//   _
// Return value:
//   _
// Errors:
//      -
// Asserts:
//   theEmptyNodeList==0. No elements are in still in use.
//
//
// T& get();
// Description:
//   get's an element from the Pool.
// Parameters:
//   _
// Return value:
//   T& the element extracted from the Pool. (element must be cleared to
//   mimick newly created element)
// Errors:
//      -
// Asserts:
//   _
//
//
// void put(T& aT);
// Description:
//   Returns an element to the pool.
// Parameters:
//   aT The element to put back in the pool
// Return value:
//   void 
// Errors:
//      -
// Asserts:
//   The pool has "empty" elements, to put element back in...
//
//===========================================================================
//
// .PRIVATE
//
//===========================================================================
 
//
// void allocate(int aSize);
// Description:
//   add aSize elements to the pool
// Parameters:
//   aSize: # of elements to add to the pool
// Return value:
//   void 
// Errors:
//      -
// Asserts:
//   _
//
//
// void deallocate();
// Description:
//   frees all elements kept in the pool.
// Parameters:
//   _
// Return value:
//   void 
// Errors:
//      -
// Asserts:
//   No elements are "empty" i.e. in use.
//
//===========================================================================
//
// .PRIVATE
//
//===========================================================================
 
//
// Pool<T>& operator=(const Pool<T>& cp);
// Description:
//   Prohibit use of assignement operator.
// Parameters:
//   cp
// Return value:
//   Pool<T>& 
// Asserts:
//   _
//
//
// Pool(const Pool<T>& cp);
// Description:
//   Prohibit use of default copy constructor.
// Parameters:
//   cp
// Return value:
//   _
// Errors:
//      -
// Asserts:
//   _
//
//
// int initSize;
// Description: size of the initial size of the pool
//
//
// int incSize;
// Description: # of elements added to the pool when pool is exhausted.
//
//
// PoolElement<T>* theFullNodeList;
// Description: List to contain all "unused" elements in the pool
//
//
// PoolElement<T>* theEmptyNodeList;
// Description: List to contain all "in use" elements in the pool
//
//-------------------------------------------------------------------------

template <class T>
class Pool
{
public:
  enum { defInitSize = 256, defIncSize  = 64 }; 
   
  Pool(int anInitSize = defInitSize, int anIncSize = defIncSize) :
    theIncSize(anIncSize),
    theTop(0),
    theCurrentSize(0),   
    theList(0)
  {
    allocate(anInitSize);
  }
  
  virtual ~Pool(void)
  {
    for (int i=0; i <theTop ; ++i)
      delete theList[i];
    
    delete []theList;
  }
  
  T* get();
  void put(T* aT);

  unsigned size(){ return theTop; };
  
protected:
  void allocate(int aSize)
  {
    T** tList = theList;
    int i;
    theList = new T*[aSize+theCurrentSize];
    // allocate full list
    for (i = 0; i < theTop; i++) {
      theList[i] = tList[i];
    }
    delete []tList;
    for (; (theTop < aSize); theTop++){
      theList[theTop] = (T*)new T;
    }
    theCurrentSize += aSize;
  }
  
private:
  Pool<T>& operator=(const Pool<T>& cp);
  Pool(const Pool<T>& cp);
  
  int theIncSize;
  int theTop;
  int theCurrentSize;
  
  T** theList;
};

//******************************************************************************
template <class T> inline T* Pool<T>::get()
{
   T* tmp;
   if( theTop == 0 )
   {
      allocate(theIncSize);
   }
   --theTop;
   tmp = theList[theTop];
   tmp->atGet();
   return tmp;
}

//
//******************************************************************************
template <class T> inline void Pool<T>::put(T* aT)
{
   theList[theTop]= aT;
   ++theTop;
}

#endif