ptr.h

a template based reference counting smart pointer, similar to <auto_ptr>,
but without the limiting exclusive ownership semantics. It uses a semaphore 
or, on supported platforms, a simple atomic exchange-and-add to achieve
thread safety without using a mutex, so it never blocks and adds only a very
small constant time overhead. The generous MIT license terms let you do pretty
much whatever you want with it as long as you dont blame me.

http://sourceforge.net/projects/ptr/