observer_ptr.h

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/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
 *
 * This library is open source and may be redistributed and/or modified under
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 *
 * This library 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
 * OpenSceneGraph Public License for more details.
*/

#ifndef OSG_OBSERVER_PTR
#define OSG_OBSERVER_PTR

#include <osg/Notify>
#include <osg/ref_ptr>
#include <osg/Observer>

#include <OpenThreads/ScopedLock>
#include <OpenThreads/Mutex>

namespace osg {

template<class T>
class observer_ptr
{
public:
    typedef T element_type;
    observer_ptr() : _reference(0), _ptr(0) {}

    observer_ptr(const ref_ptr<T>& rp)
    {
        _reference = rp.valid() ? rp->getOrCreateObserverSet() : 0;
        _ptr = (_reference.valid() && _reference->getObserverdObject()!=0) ? rp.get() : 0;
    }

    observer_ptr(T* rp)
    {
        _reference = rp ? rp->getOrCreateObserverSet() : 0;
        _ptr = (_reference.valid() && _reference->getObserverdObject()!=0) ? rp : 0;
    }

    observer_ptr(const observer_ptr& wp) :
        _reference(wp._reference),
        _ptr(wp._ptr)
    {
    }

    ~observer_ptr()
    {
    }

    observer_ptr& operator = (const observer_ptr& wp)
    {
        if (&wp==this) return *this;

        _reference = wp._reference;
        _ptr = wp._ptr;
        return *this;
    }

    observer_ptr& operator = (const ref_ptr<T>& rp)
    {
        _reference = rp.valid() ? rp->getOrCreateObserverSet() : 0;
        _ptr = (_reference.valid() && _reference->getObserverdObject()!=0) ? rp.get() : 0;
        return *this;
    }

    observer_ptr& operator = (T* rp)
    {
        _reference = rp ? rp->getOrCreateObserverSet() : 0;
        _ptr = (_reference.valid() && _reference->getObserverdObject()!=0) ? rp : 0;
        return *this;
    }

    bool lock(ref_ptr<T>& rptr) const
    {
        if (!_reference)
        {
            rptr = 0;
            return false;
        }

        Referenced* obj = _reference->addRefLock();
        if (!obj)
        {
            rptr = 0;
            return false;
        }

        rptr = _ptr;
        obj->unref_nodelete();
        return rptr.valid();
    }

    bool operator == (const observer_ptr& wp) const { return _reference == wp._reference; }
    bool operator != (const observer_ptr& wp) const { return _reference != wp._reference; }
    bool operator < (const observer_ptr& wp) const { return _reference < wp._reference; }
    bool operator > (const observer_ptr& wp) const { return _reference > wp._reference; }

    // Non-strict interface, for compatibility
    // comparison operator for const T*.
    inline bool operator == (const T* ptr) const { return _ptr == ptr; }
    inline bool operator != (const T* ptr) const { return _ptr != ptr; }
    inline bool operator < (const T* ptr) const { return _ptr < ptr; }
    inline bool operator > (const T* ptr) const { return _ptr > ptr; }

    // Convenience methods for operating on object, however, access is not automatically threadsafe.
    // To make thread safe, one should either ensure at a high level
    // that the object will not be deleted while operating on it, or
    // by using the observer_ptr<>::lock() to get a ref_ptr<> that
    // ensures the objects stay alive throughout all access to it.

    // Throw an error if _reference is null?
    inline T& operator*() const { return *_ptr; }
    inline T* operator->() const { return _ptr; }

    // get the raw C pointer
    inline T* get() const { return (_reference.valid() && _reference->getObserverdObject()!=0) ? _ptr : 0; }

    inline bool operator!() const   { return get() == 0; }
    inline bool valid() const       { return get() != 0; }

protected:

    osg::ref_ptr<ObserverSet>   _reference;
    T*                          _ptr;
};

}

#endif