base/Referenced

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/****************************************************************************
  Copyright (C)1996 David Jung <opensim@pobox.com>

  This program/file 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; either version 2 of the License, or
  (at your option) any later version.
  
  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. (http://www.gnu.org)
  
  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  
  $Id: Referenced 1029 2004-02-11 20:45:54Z jungd $
  $Revision: 1.4 $
  $Date: 2004-02-11 15:45:54 -0500 (Wed, 11 Feb 2004) $
  $Author: jungd $
 
****************************************************************************/

#ifndef _BASE_REFERENCED_
#define _BASE_REFERENCED_

#include <iostream>

namespace base {

/** Base class for intrusively referenced counted objects.
    Used by class ref */
class Referenced
{
  
public:
  Referenced() 
    : _refCount(0), onUnreferenceEnabled(false)
#ifdef DEBUG
      ,_markedForDestruction(false)
#endif
  {
#ifdef DEBUG
    // check that *this is not allocated on the stack
    //  (assumes stack is above heap in process vm space, and stack grows down)
    int onstack;
    if ( ((void*)this) > &onstack)
      throw std::runtime_error(Exception("Referenced object allocated on the stack! (only Heap allocation allowed)"));
#endif
    //if (MemoryTracer::getName((void*)this) != 0) { Logln("Initialized " << MemoryTracer::getName((void*)this) << "+" << base::MemoryTracer::getOffset((void*)this) << " ptr " << ((const void*)this) << " to " << _refCount); }
  }
      
  Referenced(const Referenced& c) 
    : _refCount(0), onUnreferenceEnabled(c.onUnreferenceEnabled)
#ifdef DEBUG
      ,_markedForDestruction(false)
#endif
  {
    //if (MemoryTracer::getName((void*)this) != 0) { Logln("Initialized " << MemoryTracer::getName((void*)this) << "+" << base::MemoryTracer::getOffset((void*)this) << " ptr " << ((const void*)this) << " to " << _refCount); }
  }  

  /** Increment the reference count by one, indicating that 
      this object has another pointer which is referencing it.*/
  inline void reference() const 
  {
    ++_refCount;
    //if (MemoryTracer::getName((void*)this) != 0) { Logln("Incremented " << MemoryTracer::getName((void*)this) << "+" << base::MemoryTracer::getOffset((void*)this) << " ptr " << ((const void*)this) << " to " << _refCount); }
#ifdef DEBUG
    if (_markedForDestruction) {
      std::cerr << "Warning: Object has been re-referenced() after being unreferenced() for the last time (deletion signalled)\n";
    }
#endif
  }


  /** Decrement the reference count by one, indicating that 
      a pointer to this object is referencing it.  If the
      refence count goes to zero, it is assumed that this object
      is nolonger referenced and is automatically deleted.*/
  inline bool unreference() const 
    { 
      --_refCount; 
      if (onUnreferenceEnabled) 
        onUnreference();

      //if (MemoryTracer::getName((void*)this) != 0) { Logln("Decremented " << MemoryTracer::getName((void*)this) << "+" << base::MemoryTracer::getOffset((void*)this) << " ptr " << ((const void*)this) << " to " << _refCount); }
      if (_refCount<=0) { 
#ifdef DEBUG
        if (_refCount < 0) {
          std::cerr << "Object has been unreferenced() too many times!\n";
          throw std::runtime_error(Exception("Object has been unreferenced() too many times!"));
        }
        else {
          if (_markedForDestruction) {
            return false; // don't destroy twice!
          }
          else {
            _markedForDestruction = true;
            //if (MemoryTracer::getName((void*)this) != 0) { Logln("Marked " << MemoryTracer::getName((void*)this) << "+" << base::MemoryTracer::getOffset((void*)this) << " ptr " << ((const void*)this) << " for deletion"); }
            return true; // signal caller to delete us
          }
        }
#else
        return true; // signal caller to delete us
#endif
      } // _refCount<=0
      return false;
    }

  /** Return the number pointers currently referencing this object. */
  inline const int referenceCount() const { return _refCount; }

  /** If enabled, each call to unreference() will also call virtual method onUnreference() */
  void enableOnUnreferenceCall(bool enabled) { onUnreferenceEnabled=enabled; }

  /** Called by unreference() if enabled via enableOnUnreferenceCall(true).  
   *  Typically overridden in subclasses that wish to know about unreference() calls - for example
   *  to handle manually breaking cyclic references
   */
  virtual void onUnreference() const {}


  
  virtual ~Referenced() 
  {
#ifdef DEBUG
    if (_refCount > 0) {
      std::cerr << "Object has been destructed with outstanding references.\n";
      throw std::runtime_error(Exception("Object has been destructed with outstanding references."));
    }
#endif
  }
  
protected:
  mutable int _refCount;
  bool onUnreferenceEnabled;
#ifdef DEBUG
  mutable bool _markedForDestruction; ///< true if _refCount has dropped to 0 after being non-zero
#endif
};

};

#endif

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