Re: [Boost-users] [multi-index] Container not safe against reentrant clear() / erase() ?

Subject: Re: [Boost-users] [multi-index] Container not safe against reentrant clear() / erase() ?
From: Joaquin M Lopez Munoz (joaquin_at_[hidden])
Date: 2009-06-03 16:47:47

Sebastian Theophil wrote:
> 
>> If I'm understanding this right, I think your design is flawed. You
> say
>> that CObjects
>> detach themselves from g_multiindex when their refcount drops to 0,
>> but:
>> how can
>> this count be zero if the CObject is still referenced from
>> g_multiindex?
> 
> 
> It seems I haven't expressed myself very clearly. Of course, the
> refcount only drops to zero when g_multiindex is cleared. But assume
> that a CObject can also be explicitly destroyed at any time.
> 

That's what I find hard to assume: how is it permissible to
destroy a CObject at any time when its refcount is not
zero? If you have some object whose lifetime is managed by
boost::shared_ptr, I think it is a bad idea to mess with
the object lifetime directly.

Please note this is not a rhetoric question: how do you know
when you explicitly destroy a CObject that you leave no
dangling boost::shared_ptrs to it?

>> On the other hand, erasing inside erase() does work; 
> 
> What I do is erase() -> ~node() -> erase() and I would guess that
> doesn't work for the same reason as before[...]
> If the container has n elements, node deletion goes through the
> following states
> 
> delete_node( node* x ) {
> 	// container has n nodes
> 	destroy(x)
> 	// container still has n nodes but x has been destroyed 
> 	reset left / right / parent pointers
> 	// container has n-1 nodes
> }
> 
> Or is that wrong? 
> 
> What I'd like is something like
> 
> delete_node( node* x ) {
> 	 reset left / right / parent pointers
>  	 // container has n-1 nodes, x has not been destructed yet
>        destroy(x)
> }
> 

The latter is the way the lib currently works. Are you experiencing
otherwise?

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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