Re: [boost] cannot pass objects of non-POD type ‘class boost::detail::shared_count’ through ‘...’; call will abort at runtime

Subject: Re: [boost] cannot pass objects of non-POD type ‘class boost::detail::shared_count’ through ‘...’; call will abort at runtime
From: Peter Dimov (pdimov_at_[hidden])
Date: 2009-09-17 08:58:23

Dave Steffen wrote:
> Hi Folks
>
> [ Sorry if this gets posted twice; my company email server changed my
> email address, and I think my first post got bounced.  Argh.]
>
> Just tried to compile my project with GCC 4.3 and Boost 1.40.  (It
> compiles and works just fine with Boost 1.38.)
>
> As part of a home-built thread-locking shared pointer thing, we have
> this code:
>
>   /// Constructor from pointer to complete type
>    template<class Y>
>    explicit shared_locking_ptr( Y * p ): px( p ), pn( p ) // Y must be
> complete
>    {
>        boost::detail::sp_enable_shared_from_this( pn, p, p );
>    }
>
> which now produces this result:
>
> ../util/thread/shared_locking_ptr.hpp:57:9: warning: cannot pass
> objects of non-POD type ‘class boost::detail::shared_count’ through
> ‘...’; call will abort at runtime
>
> In Boost 1.38, the relevent code in shared_ptr.hpp was this AFAICT:
>   #ifdef _MANAGED
>   [ ... ]
>   #else // _MANAGED
>   [...]
>
>   inline void sp_enable_shared_from_this( shared_count const &
>   /*pn*/, ... ) {
>   }
>
>   #endif // _MANAGED
>
> In 1.40, it's been changed to
>
>
>   #ifdef _MANAGED
>   [...]
>   #else // _MANAGED
>
>   inline void sp_enable_shared_from_this( ... )
>   {
>   }
>
>   #endif // _MANAGED
>
>
> Does anyone know why the change?

The signature of sp_enable_shared_from_this has changed, it now takes a 
pointer to a shared_ptr as its first argument. Look at the current 
shared_ptr constructor:

    template<class Y>
    explicit shared_ptr( Y * p ): px( p ), pn( p ) // Y must be complete
    {
        boost::detail::sp_enable_shared_from_this( this, p, p );
    }

Relying on implementation details has its maintenance costs. :-) You'll 
probably need to refactor shared_locking_ptr to contain (or privately derive 
from) a shared_ptr.