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

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-04-18 06:21:30

Eric Niebler wrote:
> Peter Dimov wrote:
>> Eric Niebler wrote:
>>> Peter Dimov wrote:
>>
>>>> Seeing so many variations of it is a pretty good indication that we
>>>> need it in Boost. :-)
>>> So you're going to add it? :-)
>>
>> I can't help but think that even if I did add the above, you
>> wouldn't use it because of the virtual destructor,
>
>
> You're right, because in xpressive alone I use counted_base in no less
> than 3 places where the virtual destructor would be needless overhead!
> Clearly, it can't be all that uncommon.

It may be common. The point is that we need to settle on a single version of 
boost::counted_base. The virtual destructor version does have its benefits: 
it's easier to understand and use (CRTP can be a bit hard to swallow) and it 
allows intrusive_ptr<counted_base> to be used as the intrusive version of 
shared_ptr<void> and void* (with the additional benefit of a working 
dynamic_cast.)

counted_base is somewhat bicycle sheddish and I've considered adding one as 
documentation rather than code. But one problem with that is atomic_count 
being in detail. :-)

> The following program exposes the problem for me with vc7.1, vc8 and
> gcc 3.4.4. If you comment out the friend functions and uncomment the
> global free functions, the problem goes away. I don't understand it --
> is some name look-up subtlety at play here?

I don't understand it either. Comeau/EDG compiles it. A non-template 
counted_base doesn't have this problem, FWIW.