Re: [Boost-users] Is weak_ptr lock method thread safe?

Subject: Re: [Boost-users] Is weak_ptr lock method thread safe?
From: Slava (Viatcheslav.Sysoltsev_at_[hidden])
Date: 2013-04-24 02:56:05

On Tue, 23 Apr 2013 18:25:40 +0200, Klaim - Joël Lamotte  
<mjklaim_at_[hidden]> wrote:

> On Mon, Apr 22, 2013 at 10:26 AM, Andrea Galeazzi <galeazzi_at_[hidden]>  
> wrote:
>
>> In other words, is lock method atomic in respect to deference of the
>> shared point?
>
>
> Yes it is thread-safe, that's the whole point of the system:
> shared_ptr is implemented (in boost or std implementations) with an  
> atomic
> counter used to sync the moment when the object need to be destroyed.

Sure? Looking at boost 1.53 headers I see it is not thread safe:

template<class T> class weak_ptr
{
...
     shared_ptr<T> lock() const BOOST_NOEXCEPT
     {
         return shared_ptr<T>( *this, boost::detail::sp_nothrow_tag() );
     }
...
}

template<class T> class shared_ptr
{
...
     template<class Y>
     shared_ptr( weak_ptr<Y> const & r, boost::detail::sp_nothrow_tag )
     BOOST_NOEXCEPT : px( 0 ), pn( r.pn, boost::detail::sp_nothrow_tag() )
     {
         if( !pn.empty() )
         {
             px = r.px;
         }
     }
...
}

-- Slava