Question

I want a pointer where I can tell when the reference count is one. Essentially the pointer works like a weak_ptr, but the cleanup needs to be manual. That is, every so often the program goes through a loop of its pointers and checks which ones have only one reference remaining. Some it will clean, others it will retain a while longer (in case somebody needs it again).

Now, I know how to do this using a combination of a custom cleanup function and weak_ptr. I just think the same thing could be accomplished, with simpler code, if I could simply figure out when only one user of the shared_ptr remains.

I know that shared_ptr has a use_count function, but it has this ominous note in the docs: “…not necessarily efficient. Use only for debugging and testing purposes…” Naturally I’m not so keen on using something with such a warning. I don’t really need the count anyway, just a way to detect when there is only one left.

Is there some boost wrapper that achieves what I want (can be in any library)? Or must I use the technique I already know of custom cleanup function combined with a weak_ptr?

Answer 1

You cannot in general accurately determine the number of references. But you can tell when it is exactly one – use unique().