Andreas Huber wrote:
Eric Niebler wrote: [snipped]
FWIW, I rolled my own counted_base class for statechart. It can be found here: http://cvs.sourceforge.net/viewcvs.py/boost/boost/boost/statechart/detail/co...
I'd also be interested in intrusive_ptr providing a class along the lines of counted_base...
I've added something similar to your counted_base to xpressive, and it works well. I think there is a clear need for this to be a standard part of intrusive_ptr. A quick grep through the archives turns up several requests for this functionality, including a recent request from Ulrich Eckhardt. The implementation is quite trivial (see below). Peter, can this (or something like it) just be added to intrusive_ptr.hpp, or should we go through a fast-track review? If you want to just add it, I can see what I can do about tests and docs. Open questions: 1) What about the name (counted_base)? Can we do better? 2) Should there be a way to get the actual ref-count, or is bool unique() enough (like shared_ptr)? <<< Begin Code >> ////////////////////////////////////////////////////////////////////////////// // (c) Copyright Andreas Huber Doenni 2002-2005, Eric Niebler 2006 // Distributed under the Boost Software License, Version 1.0. (See // accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) ////////////////////////////////////////////////////////////////////////////// #ifndef BOOST_XPRESSIVE_DETAIL_UTILITY_COUNTED_BASE_HPP_EAN_04_16_2006 #define BOOST_XPRESSIVE_DETAIL_UTILITY_COUNTED_BASE_HPP_EAN_04_16_2006 #include <boost/assert.hpp> #include <boost/noncopyable.hpp> #include <boost/checked_delete.hpp> #include <boost/detail/atomic_count.hpp> namespace boost { namespace xpressive { namespace detail { template<typename Derived> struct counted_base_access; //////////////////////////////////////////////////////////////////// // counted_base template<typename Derived> struct counted_base : private noncopyable { bool unique() const { return 1 == this->count_; } protected: counted_base() : count_(0) { } private: friend struct counted_base_access<Derived>; mutable boost::detail::atomic_count count_; }; //////////////////////////////////////////////////////////////////// // counted_base_access template<typename Derived> struct counted_base_access { static void add_ref(counted_base<Derived> const *that) { ++that->count_; } static void release(counted_base<Derived> const *that) { BOOST_ASSERT(0 < that->count_); if(0 == --that->count_) { boost::checked_delete( static_cast<Derived const *>(that)); } } }; template<typename Derived> inline void intrusive_ptr_add_ref(counted_base<Derived> const *that) { counted_base_access<Derived>::add_ref(that); } template<typename Derived> inline void intrusive_ptr_release(counted_base<Derived> const *that) { counted_base_access<Derived>::release(that); } }}} // namespace boost::xpressive::detail #endif -- Eric Niebler Boost Consulting www.boost-consulting.com