Re: [boost] Re: shared_ptr and BOOST_DISABLE_THREADS

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2004-04-25 09:45:32

On Apr 25, 2004, at 7:00 AM, John Maddock wrote:

> Maybe, but lets not forget that shared_ptr doesn't need a mutex at 
> all, what
> it needs is an atomic counter (actually less than that, because we 
> never
> need the value of the counter just whether it's less than/greater 
> than, or
> equal to zero).

shared_ptr has two counts which sometimes must both be incremented in 
an atomic fashion.

> template <class T, bool threaded = BOOST_SP_DEFAULT>
> class shared_ptr;
>
> Which I think I'm right in saying would be std conforming (because 
> we're
> permitted additional defaulted template parameters right?), and would 
> also
> quash any potential ODR violations.

Actually no, it would not be standard conforming for a hypothetical 
std::shared_ptr, unless the standard granted specific permission for 
this one template. (or specified the defaulted template in the first 
place)

http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-closed.html#94

-Howard