Re: [Boost-users] shared_ptr<T> callback

Subject: Re: [Boost-users] shared_ptr<T> callback
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2009-09-15 00:28:33

On Mon, Sep 14, 2009 at 7:41 PM, Vjekoslav Brajkovic
<balkan_at_[hidden]> wrote:
> Hello! :)
>
> I'm writing a write-through cache unit which returns const shared_ptr<T>.
> Â After the data has been modified and once share_ptr goes out of scope, I
> would like the shared_ptr destructor to call a handler which would commit
> the modified value to some other location  -- a DHT for instance.  Is there
> a way to supply a callback function to shared_ptr destructor? Â Any help
> would be greatly appreciated.
>
> Please let me know if the question is too ambiguous.

If you read the docs, you notice it can take a destructor argument as
well, on the synopsis page you can see it has some constructors that
take it:  http://www.boost.org/doc/libs/1_40_0/libs/smart_ptr/shared_ptr.htm.
 Copying a good section from that page:

Custom deallocators allow a factory function returning a shared_ptr
to insulate the user from its memory allocation strategy. Since the
deallocator is not part of the type, changing the allocation strategy
does not break source or binary compatibility, and does not require a
client recompilation. For example, a "no-op" deallocator is useful
when returning a shared_ptr  to a statically allocated object, and
other variations allow a shared_ptr  to be used as a wrapper for
another smart pointer, easing interoperability.

The support for custom deallocators does not impose significant
overhead. Other shared_ptr features still require a deallocator to be
kept.

The requirement that the copy constructor of D does not throw comes
from the pass by value. If the copy constructor throws, the pointer is
leaked. Removing the requirement requires a pass by (const) reference.