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

24 Apr 2013


      Il 24/04/2013 8.56, Slava ha scritto:
...
On Tue, 23 Apr 2013 18:25:40 +0200, Klaim - Joël Lamotte 
 wrote:
...
On Mon, Apr 22, 2013 at 10:26 AM, Andrea Galeazzi  
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
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So is it thread safe or not?