include/xapian/base.h

/* base.h: Reference-counted pointers
 *
 * Copyright 1999,2000,2001 BrightStation PLC
 * Copyright 2002 Ananova Ltd
 * Copyright 2002,2003,2004,2007 Olly Betts
 *
 * 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; 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.
 *
 * 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 XAPIAN_INCLUDED_BASE_H
#define XAPIAN_INCLUDED_BASE_H

#include <xapian/deprecated.h>

namespace Xapian {
namespace Internal {

class RefCntBase {
    /* Note: We never delete a pointer to a subclass of RefCntBase using
     * a RefCntBase *, so we don't need a virtual destructor here.
     */
    protected:
        RefCntBase(const RefCntBase &) : ref_count(0) { }

    public:
        RefCntBase() : ref_count(0) { }

        typedef unsigned int ref_count_t;

        mutable ref_count_t ref_count;
};

template <class T>
class RefCntPtr {
    private:
        T *dest;

    public:
        T *operator->() const;
        T &operator*() const;
        T *get() const;
        RefCntPtr(T *dest_);
        RefCntPtr();
        RefCntPtr(const RefCntPtr &other);
        void operator=(const RefCntPtr &other);
        void operator=(T *dest_);
        ~RefCntPtr();

        template <class U>
        RefCntPtr(const RefCntPtr<U> &other);
};

template <class T>
inline RefCntPtr<T>::RefCntPtr(T *dest_) : dest(dest_)
{
    if (dest) ++dest->ref_count;
}

template <class T>
inline RefCntPtr<T>::RefCntPtr() : dest(0)
{
}

template <class T>
inline RefCntPtr<T>::RefCntPtr(const RefCntPtr &other) : dest(other.dest)
{
    if (dest) ++dest->ref_count;
}

template <class T>
inline void RefCntPtr<T>::operator=(const RefCntPtr &other) {
    operator=(other.dest);
}

template <class T>
inline void RefCntPtr<T>::operator=(T *dest_) {
    // check if we're assigning a pointer to itself
    if (dest == dest_) return;

    // copy the new dest in before we delete the old to avoid a small
    // window in which dest points to a deleted object
    // FIXME: if pointer assignment isn't atomic, we ought to use locking...
    T *old_dest = dest;
    dest = dest_;
    if (dest) ++dest->ref_count;
    if (old_dest && --old_dest->ref_count == 0) delete old_dest;
}

template <class T>
inline RefCntPtr<T>::~RefCntPtr()
{
    if (dest && --dest->ref_count == 0) {
        // zero before we delete to avoid a small window in which dest points
        // to a deleted object
        // FIXME: if pointer assignment isn't atomic, we ought to use locking...
        T * condemned = dest;
        dest = 0;
        delete condemned;
    }
}

template <class T>
template <class U>
inline
RefCntPtr<T>::RefCntPtr(const RefCntPtr<U> &other)
        : dest(other.get())
{
    if (dest) ++dest->ref_count;
}

template <class T>
inline T *RefCntPtr<T>::operator->() const
{
    return dest;
}

template <class T>
inline T &RefCntPtr<T>::operator*() const
{
    return *dest;
}

template <class T>
inline T *RefCntPtr<T>::get() const
{
    return dest;
}

}
}

#endif /* XAPIAN_INCLUDED_BASE_H */

---