lockingptr.h

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/******************************************************************************
 *
 * $Id: $
 *
 * Copyright (C) 1997-2008 by Dimitri van Heesch.
 *
 * Permission to use, copy, modify, and distribute this software and its
 * documentation under the terms of the GNU General Public License is hereby 
 * granted. No representations are made about the suitability of this software 
 * for any purpose. It is provided "as is" without express or implied warranty.
 * See the GNU General Public License for more details.
 *
 * Documents produced by Doxygen are derivative works derived from the
 * input used in their production; they are not affected by this license.
 *
 */

#ifndef LOCKINGPTR_H
#define LOCKINGPTR_H

class LockableObj
{
  public:
    LockableObj() : m_lockCount(0) {}
    virtual ~LockableObj() {}

    bool isLocked() const { return m_lockCount>0; }

//VC++6.0 workaround
//  protected:
    virtual void lock() const = 0;

    virtual void unlock() const = 0;

//VC++6.0 workaround
//  private:
//    template<class T> friend class LockingPtr;
    int  m_lockCount;
};

template<class T> class LockingPtr
{
    LockableObj *m_owner;
    const T *m_ptr;

  public:
    LockingPtr(const LockableObj *o,const T* p) 
    { 
      if (o->m_lockCount==0) o->lock(); 
      m_owner = (LockableObj *)o;
      m_owner->m_lockCount++;
      m_ptr = p;
    }
    
    LockingPtr(const LockingPtr &lp)
    {
      m_ptr   = lp.m_ptr;
      m_owner = lp.m_owner;
      m_owner->m_lockCount++;
    }

    LockingPtr &operator=(const LockingPtr &lp)
    {
      m_owner->m_lockCount--;
      if (m_owner->m_lockCount==0) // no more references
      {
        m_owner->unlock(); 
      }
      m_ptr   = lp.m_ptr;
      m_owner = lp.m_owner;
      m_owner->m_lockCount++;
      return *this;
    }

    ~LockingPtr() 
    { 
      m_owner->m_lockCount--;
      if (m_owner->m_lockCount==0) // no more references
      {
        m_owner->unlock(); 
      }
    }

    bool isNull() const
    {
      return m_ptr==0;
    }

    bool operator!() const
    {
      return !m_ptr;
    }

    bool operator==(T *p) const
    {
      return m_ptr==p;
    }

    bool operator==(const LockingPtr &lp) const
    {
      return m_ptr==lp.m_ptr;
    }

    bool operator!=(T *p) const
    {
      return m_ptr!=p;
    }

    bool operator!=(const LockingPtr &lp) const
    {
      return m_ptr!=lp.m_ptr;
    }

    const T& operator* () const
    { 
      return *m_ptr; 
    }

    T* pointer() const
    {
      return (T*)m_ptr;
    }
    
    T* operator-> () const
    { 
      return (T*)m_ptr; 
    }
};

#endif // LOCKINGPTR_H

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