Re: [boost] [intrusive_ptr] atomic ref counting?

From: Eric Niebler (eric_at_[hidden])
Date: 2006-04-17 18:00:47

Peter Dimov wrote:
> Eric Niebler wrote:
> 
>> The implementation is quite trivial (see below).
> 
> Seems pretty complicated to me. The "canonical" counted_base is (assuming 
> namespace boost):
> 
> class counted_base
> {
> private:
> 
>     mutable detail::atomic_count count_;
> 
> protected:
> 
>     counted_base(): count_( 0 ) {}
>     virtual ~counted_base() {}

Using CRTP (as in the code I posted) avoids the need for a virtual 
destructor. I see no need to force the virtual on people.

>     counted_base( counted_base const & ): count_( 0 ) {}
>     counted_base& operator=( counted_base const & ) { return *this; }

Huh. I was thinking it was safer to make these guys noncopyable, but ok.

> public:
> 
>     inline friend void intrusive_ptr_add_ref( counted_base const * p )
>     {
>         ++p->count_;
>     }
> 
>     inline friend void intrusive_ptr_release( counted_base const * p )
>     {
>         if( --p->count_ == 0 ) delete p;
>     }

Tried that. Under certain circumstances, VC7.1 wasn't finding the friend 
functions. Hence my counted_base_access hack, and the 
intrusive_ptr_add_ref/release functions at namespace scope.

>     long use_count() const { return count_; }

Sure.

> };
> 
> Seeing so many variations of it is a pretty good indication that we need it 
> in Boost. :-)

So you're going to add it? :-)

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com