[boost] interest poll: smart pointers that handle circular references

From: Ariane van der Steldt (ariane_at_[hidden])
Date: 2007-04-10 01:34:52

Hello,

I was wondering if there's interest in a smart pointer, which is able to 
cope with circular references. I think it would make a nice addition to 
the smart_ptr classes already in boost.

I have a library almost ready, which can solve the problem where:
- class A contains a pointer to class B
- class B contains a pointer to class A
- and it is not known wether the "master" of these two is A or B.

With "master", I mean which pointer is the pointer that is kept alive 
from the execution thread. For example, if we would implement this with 
shared_ptr and weak_ptr, we would most likely have the following:
- class A contains a shared_ptr to class B
- class B contains a weak_ptr to class A
- the execution thread contains a shared_ptr Ptr to class A.
In this case, if I where to assign Ptr = B, A would be erased, since A 
no longer is referenced (weak_ptr references don't count 
reference-counter wise).

The code I have aims to solve this problem, by using two types of 
pointers. The execution thread will work with boost::intrusive_ptr 
(which are allocated on the stack) while classes wishing to point to 
other classes, will use a new type of pointer (named 'reference') that I 
designed. This pointer is aware of the owner of the pointer, in addition 
of the object it points to.

The implementation uses only standard C++ code, with some help from 
boost (notably boost::intrusive_ptr and, in the case of multithreading 
environments, boost::thread).

Anyways, I am wondering if people are interested. :) Can't imagine that 
it wouldn't be of use to at least some of you. ;)

For status info: I am currently ironing out some minor bugs and 
implementing STL-type collection classes (like the equivalent of a 
std::list<MyClass*> ) for these pointers, as they have non-standard 
initialization semantics.

Ariane