[boost] Re: Intrusive/invasive smart pointer?

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2000-01-12 14:24:07

From: Beman Dawes <beman_at_[hidden]>
> In implementing a B-tree Container for boost, I have a smart pointer
> need which can't be met by boost::shared_ptr<>; an intrusive
> reference count is required.  (Of the three reasons, the last one is
> the killer.)
> 
> *  Since the smart point goes in an iterator, it would be better to
> avoid the size and separate allocation penalty of shared_ptr.
> 
> *  Memory allocation should use the container's Allocator.
> 
> *  The smart pointer needs to support construction from a raw pointer
> when other smart pointers to the same object are known to exist, but
> are not available. This means there needs to be a constructor which
> increments the reference count rather than just setting it to 1.
> (This need derives from a really nice cache design which holds raw
> pointers rather than smart pointers.  If smart pointers where held,
> the cached pages would never get released.)

So you are using the raw pointers as weak pointers in this design?

> There are two ways I can see to deal with this:
> 
> 1)  General solution: add a boost::shared_in_ptr<> template to
> boost/smart_ptr.hpp which has the same interface as
> boost::shared_ptr<>, except for one additional constructor.

Or the old shared_ptr<T,Allocator> proposal, where the Allocator
allocates the count as well as the T.
 
> 2)  Specific solution: supply a minimal pointer within the B-tree
> implementation that solves that specific problem only.
> 
> Opinions, anyone?
> 
> --Beman