[boost] Re: [shared_ptr] dealing with shared_ptr and cycles

From: David Abrahams (dave_at_[hidden])
Date: 2005-06-06 11:08:15

Lorenzo Bettini <bettini_at_[hidden]> writes:

> Jonathan Wakely wrote:
>> On Mon, Jun 06, 2005 at 03:58:41PM +0200, Lorenzo Bettini wrote:
>> 
>>>However, it is not clear to me how to use weak_ptr in this context...
>>>
>>>can some one provide some clue, please?
>> Well, for this context:
>>     class C;
>>     typedef boost::shared_ptr<C> CP;
>>     typedef boost::weak_ptr<C>   WP;
>>     class C
>>     {
>>     private:
>>       string s;
>>       WP wp;
>>     public:
>>       C(const string &ss, CP c = CP()) : s(ss), wp(c) {}
>>       void set(CP c) { wp = c; }
>>       ~C() { cout << "destroying C" << endl; }
>>     };
>> Then main() would be unchanged.
>> That might not work for anything less trivial than your example,
>> since
>> you'd need to ensure the shared_ptrs that own the objects are still
>> around when you use the weak_ptrs.
>
> indeed, it only works for that simple main: the main problem I had is 
> just "ensure the shared_ptrs that own the objects are still
> around when you use the weak_ptrs.".
>
> Moreover, I had to deal with mutual dependences, and this makes the 
> whole thing worse...

Can you deal with deallocation of the whole network at once?  It often
works to maintain the nodes (C objects) in a container like a deque
and let them link to one another with raw pointers.

Otherwise you may be in need of a real GC.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com