Re: [boost] [smart_ptr] questions about some regression test cases

From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2008-04-28 22:24:05

On Monday 28 April 2008 13:38, Daniel Frey wrote:
> I hope it's OK if we discuss it now. So far, I was under the impression
> that calling shared_from_this() requires that some other shared_ptr
> takes ownership later. BOOST_ASSERT( _shared_count.empty() ) tests
> exactly that. It's an easy to understand rule and I can see the use
> cases.
>
> How would you describe/document the behavior you had in mind? What use
> case would it serve?

It asserts that no dangling shared_ptrs exist, or that a shared_ptr has 
taken ownership (in which case it is assumed the user knows what they are 
doing).  It permits, for example, weak_ptrs to exist which might be used 
to track the object's lifetime whether or not it is actually managed by a 
shared_ptr.  To be more concrete, you might have an object which uses Qt 
signals/slots and whose lifetime is managed by the Qt framework.  You 
could use shared_from_this() to get a weak_ptr that can be used to track 
the object's lifetime by thread_safe_signals, for automatic connection 
management of additional signals/slots from thread_safe_signals.  It would 
work equivalently to boost::trackable from the current boost.signals.

On the other hand, I can't think of any situation where aborting on the "no 
owner and no dangling shared_ptr" case would actually provide any 
additional safety over allowing it.

-- 
Frank