[boost] [shared_ptr] enable_shared_from_any - patch & files

Subject: [boost] [shared_ptr] enable_shared_from_any - patch & files
From: Philip Warner (pjw_at_[hidden])
Date: 2010-05-18 01:17:53

>
> Specifically, what I would like to see is a solution to the following code:
>
>      C1 *p = new C1();
>      shared_ptr<C1> ptr(p);
>      ...
>      ...some time later....
>      shared_ptr<C1> ptr2<p>;
>
>  and the resulting mess because of double-deallocation. 
>   
...
> I am very happy to provide a patch that:
>
>  - adds a class, enable_shared_from_any, that can be inherited from
>  - updates shared_ptr to work in the above code, if C1 inherits from
> enable_shared_from_any
>   

If people are interested, the patch is attached. It includes a patch
file as well as final versions of the files.

'sp_enable_shared_from_this' now returns a value; for old-style
shared_ptr objects this is a constant 'false'. Allocation of the
shared_counter object has been deferred until the
'sp_enable_shared_from_this'; if the result is true, it is assumed that
the shared_counter has been allocated/copied. Otherwise, the
shared_counter is allocated in the constructor.

There used to be an extra 'sp_enable_shared_from_this'for each of the
possible base classes (enable_shared_from_this and
enable_shared_from_this2); now there are three for each possible base
class because we have to pass the various possible allocator/deallocator
parameters to the template functions.

There is scope here to remove both enable_shared_from_this and
enable_shared_from_this2 since, I believe, enable_shared_from_any is
capable of performing both the tasks that these were intended for, but I
have not done this. I will do so if people prefer. There are a number of
different ways this could be done for backward compatibility.

The patch is against 1.43.0.